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Astronomy and Astrophysics in the New Millennium: Panel Reports (2001)

Chapter: 2 Report of the Panel on Optical and Infrared Astronomy from the Ground

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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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2
Report of the Panel on Optical and Infrared Astronomy from the Ground

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

SUMMARY

As we cross the threshold of the new millennium, astronomy with ground-based optical and infrared (O/IR) telescopes will continue to play its fundamental role in shaping our understanding of the workings of the universe, enriching the golden era of discovery that astronomy has enjoyed in the last decades. As a result of past investments in astronomical facilities, the United States led the world in observational research throughout the 20th century. Our nation has the talent, the knowledge, and the resources to carry this great tradition of leadership into the 21st century, building on a generation of powerful 8-m-class telescopes and anticipating future telescope facilities of unprecedented power and resolution.

However, state-of-the-art, ground-based O/IR facilities have grown in scale and complexity so that a new paradigm is needed that balances diversity and coordination. This paradigm focuses effort on unique and complementary capabilities and will enable the efficient development and operation of the next generation of facilities together with the effective use of existing ones. Establishing a common vision within the astronomy community of how these facilities should evolve is the foundation of the recommendations of the Panel on Optical and Infrared Astronomy from the Ground for the coming decade. In this context, the panel proposes three initiatives to encourage the evolution of U.S. O/IR ground-based facilities as a system, by combining and coordinating the assets and efforts of federally funded and independent observatories:

  • A next-generation, giant-aperture, adaptive-optics-equipped telescope whose spatial and spectral resolution will enable the unraveling of complex physical processes in the first galaxies, in nearby planetary systems, and in newborn stars. A unique opportunity exists to bring together federal and independent observatories to build and operate this facility.

  • A large-aperture, very-wide-field synoptic survey telescope that will search the solar system for its ancient materials and open a new time window on astronomical phenomena. This facility has particular resonance with the new role envisioned for the National Optical Astronomy Observatories (NOAO).

  • An enhanced instrumentation program for independent observatories that capitalizes on and encourages the significant investment of

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

nonfederal funds, both to maximize the operation of U.S. facilities as an efficient system and to increase public access to these facilities.

The panel has translated these generalized initiatives into concrete recommendations and prioritized them.

MAJOR INITIATIVE, PRIORITY ONE: GSMT

Develop the technology to build a giant (30-m class) segmented-mirror, adaptive-optics-equipped, ground-based O/IR telescope (GSMT) and begin its construction within the decade. With diffraction-limited performance down to at least 1 µm, an order-of-magnitude increase in light-gathering power, and a factor-of-4 gain in spatial resolution, GSMT will enable breakthrough science in studies of star and planet formation, stellar populations, and early galaxy evolution. The GSMT’s spatial resolution of 14 milliarcsec at 2 µm and its high spectral resolution in the near-infrared region will significantly exceed the performance of the Next Generation Space Telescope (NGST, scheduled for launch in 2008), providing an important complementarity such as that developed between the Hubble Space Telescope and the Keck telescopes. Furthermore, with the ability to add new instrumentation to GSMT, its capabilities can evolve in response to scientific advances in the early NGST-GSMT era, making it more productive and developing the scientific case for even more advanced facilities on the ground and in space. The GSMT will push relevant technology such as adaptive optics (AO) to its limits, toward what could be the ultimate ground-based telescope in the decades to come. The panel recognizes that, even with anticipated innovation in design and technology, construction of this facility requires an enormous investment of resources, perhaps exceeding $400 million; the operating costs will be similarly large over the facility’s lifetime.1 In response to the challenge of garnering such huge resources, the panel emphasizes its belief that GSMT offers a golden opportunity for partnership between national and independent observatories. To assure the maximum science return, it is essential that a broad scientific community have

1  

The estimated costs for ground-based initiatives that appear in the survey committee report (Astronomy and Astrophysics Survey Committee, National Research Council. 2001. Astronomy and Astrophysics in the New Millennium, Washington, D.C.: National Academy Press) include instrumentation, grants, and operations, as described in the preface. These costs for the GSMT are estimated be about $200 million.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

access to GSMT; the panel believes that public access should be maximized within the constraints of available funding and that the partnership between the public and private components of U.S. O/IR ground-based astronomy should be strengthened.

MAJOR INITIATIVE, PRIORITY TWO: LSST

Build a large-aperture (6.5-m class), very-wide-field (~3 deg) synoptic survey telescope (LSST) to produce a periodic digital map of the sky. Its unique combination of large aperture and wide field (~10 deg2) will allow LSST to map the entire sky down to 24th magnitude in a few days. Such capability will enable a wide-area variability experiment (WAVE), a finite-duration project that will accomplish many important scientific goals through a small number of simple survey modes. For example, WAVE on LSST will do the following:

  • Discover and track 10,000 objects in the Kuiper Belt, a largely unexplored, primordial component of our solar system.

  • Locate potentially threatening near-Earth objects (NEOs) down to 300 m in size.

  • Discover and monitor many kinds of variable objects, including supernovae, active galactic nuclei (AGN), and microlensed stars.

  • Produce extremely deep images over hundreds of square degrees for studying the distribution of dark matter through weak gravitational lensing.

More than just a telescope, LSST with WAVE will make important strides in data processing, data mining tools, and archiving components and will play a key role in the National Virtual Observatory (NVO) described in the survey committee report. Its data product will have widespread application to all fields of astrophysics and will have enormous educational potential by virtue of its ability to produce a “living sky” that can be downloaded in the classroom. While this unique, state-of-the-art facility could capitalize on the complementary strengths of independent observatories, its mode of operation and data product would make LSST an ideal undertaking for NOAO in its developing new role.

MODERATE INITIATIVE, PRIORITY ONE: TSIP

Support the Telescope System Instrumentation Program (TSIP) to foster

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

the more coherent development of public and independent telescope facilities and to increase public access. By substantially increasing its funding of instrumentation for the new generation of large-aperture telescopes at independent observatories, the NSF would encourage the continuation of substantial nonfederal investments, leverage their scientific productivity, and open up new observing opportunities for the entire U.S. astronomy community. The panel therefore proposes TSIP, which would fulfill this critical need and encourage the evolution of U.S. ground-based O/IR facilities as a coherent system. Particularly in an era of enormous investment by the European Southern Observatory, the systemization of all U.S. resources is essential to maintain leadership in the field. Leadership in astronomy is important not only to the discipline itself, but also to the vital role that astronomy plays in improving the scientific literacy of the public.

SCIENCE OPPORTUNITIES

ANSWERING FUNDAMENTAL QUESTIONS

The world’s astronomy community has built powerful tools with which to answer fundamental questions about the birth of galaxies, stars, and planets and to explore the most exotic phenomena in the universe. These tools include (1) a new generation of ground-based O/IR telescopes, (2) the powerful new millimeter-wave arrays—the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the Submillimeter Array (SMA), with the Atacama Large Millimeter Array (ALMA) to come later in the decade, and (3) the Hubble Space Telescope (HST) and Chandra X-ray Observatory, now in operation, the Space Infrared Telescope Facility (SIRTF) and the Space Interferometry Mission (SIM), on the way, and the Next Generation Space Telescope (NGST), to come. Properly instrumented and supported, these facilities will provide unprecedented opportunities to solve many of the mysteries that 20th century astronomical exploration uncovered. In this chapter, the panel recommends two additional ground-based O/IR facilities—a 30-m-class telescope (GSMT) and a large-aperture synoptic survey telescope (LSST) —which, in concert with the above facilities, will enable astronomers to accomplish the following goals over the next decade or two:

  • Describe the complete cosmological state of the universe with

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

better than 10 percent accuracy. Using type Ia supernovae and other standard candles, gravitational lenses, and the Sunyaev-Zel’dovich effect, test the Friedmann-Robertson-Walker model back to z~3. Is the universe accelerating as a result of dark energy?

  • Follow the history of star formation and chemical evolution over all of cosmic time. Find and characterize the first generation of stars in the early universe and relate these to the oldest stars in our galaxy and its neighbors. Chart chemical evolution in stars and the interstellar medium through star-by-star studies in nearby galaxies and integrated galaxy-light measurements back to the earliest galaxies. Balance the baryon budget: describe the location and nature of all the baryons through cosmic time.

  • Test the hierarchical model of galaxy formation: observe and analyze the assembly of galaxies from the earliest star systems. Follow the buildup of large-scale structure from reionization to the present day and connect the evolution of individual galaxies to their environment within large-scale structure. Map the dark matter and galaxy distributions with sufficient precision to understand the role of dark matter in galaxy formation and obtain clues to its nature.

  • Connect the formation of supermassive black holes to galaxy formation and evolution. Discover the epoch of black hole formation, the dynamics of the process, and the relation to star formation in the nuclei of galaxies. Understand better the physical processes in active galactic nuclei and solve the riddle of gamma-ray bursts.

  • Examine in detail the processes of star and planet formation. Describe the accretion process that forms a star, including the physical properties of the raw material and the dynamic processes from molecular cloud formation to nuclear ignition. Study the evolution of planetary disks and observe the building of planets around nearby stars, from Kuiper Belt objects (KBOs) at the 100-AU zone to the 1-AU zone, where Earth-like worlds could be formed.

  • Analyze the surviving building blocks of the solar system. Map the Kuiper Belt in our solar system and measure the physical characteristics of KBOs as examples of the primordial material that built the planets. Identify all NEOs whose impact with Earth could have catastrophic consequences.

  • Take a census of the planetary populations around other stars. Understand the relationship between brown dwarfs and planets and the distribution of giant planets in neighboring systems. Search for worlds that could, or already do, support life as we know it.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

These are ambitious goals, and ground-based O/IR facilities will play a substantial, often crucial, part in achieving them. Despite the large foreign investments around the world in ground-based astronomy, the United States is well positioned to maintain its leadership role in this field.

EXPLOITING THE DIVERSE, UNIQUE FACILITIES OF U.S. GROUND-BASED O/IR ASTRONOMY

Astronomers now probe the physics of exotic and extreme environments using observations across the electromagnetic spectrum, ranging from radio waves to gamma rays and everything in between. Ground-based O/IR research remains at the heart of this endeavor. Ground-based spectroscopic observations have been crucial to research with the HST for such diverse topics as high-redshift galaxies, the extragalactic distance scale and cosmological parameters, and stellar populations in the Milky Way and other nearby galaxies. The study of radio galaxies relies on a combination of radio, optical, and infrared (IR) data, as does the goal of linking the evolution of the interstellar medium to stellar evolution. The x-ray halos of galaxies and the hot interstellar gas in rich clusters are being understood thanks to both space-based observations and ground-based optical data, and the recent discovery that gamma-ray bursts take place in distant galaxies, making them the most energetic known phenomenon, is the result of hard-won spectroscopic data from the Keck telescopes and rapid-response imaging from a variety of ground-based instruments.

The ambitious scientific program outlined above requires a broad suite of telescopes with a range of aperture sizes and powerful state-of-the-art instrumentation employing the latest array detectors. Ground-based O/IR facilities available to U.S. astronomers include both national and independent installations in a unique combination that has kept U.S. astronomy strong. Remarkably, most of the glass resides at independent observatories, but the National Science Foundation’s (NSF’s) role is nevertheless vital to the health of the entire enterprise: NSF not only supports NOAO and Gemini but also plays a crucial role at the independent observatories by virtue of its grant support for research and instrumentation.

Strong competition for leadership in astronomy is now coming from the European Southern Observatory (ESO), which has made huge investments at two Chilean observatories. The most recent of the investments was for the Very Large Telescope (VLT), four 8-m telescopes at

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

Cerro Paranal costing approximately $700 million. Eight first-generation instruments are under construction at a cost of approximately $90 million. An ongoing instrumentation program funded at $10 million per year is anticipated to provide state-of-the art facilities throughout the decade. A world-class interferometer is also under construction for the VLT. Early results from the VLT are impressive. In addition, ESO has announced its intention to build a truly enormous telescope, currently planned to have a 100-m aperture; this billion-dollar-plus initiative is unprecedented in the history of ground-based astronomy.

To meet this challenge, the United States must use its unique combination of federal, state, and private resources to best advantage. The spirit of independence and individual initiative that has characterized U.S. ground-based O/IR astronomy should continue, for it has had highly productive and creative results. But federal resources are sufficiently scarce, and the need at both national and independent observatories so acute that a greater degree of cooperation is urgently needed. Put simply, the suite of U.S. observatories should function as a coherent system to ensure that U.S. astronomers will have the means to participate fully in pursuing the fundamental goals outlined above. Although the recommended new facilities and programs described below are completely justified by scientific arguments alone, the panel sees as equally important the additional overarching goal of strengthening the system and creating a process for its development. To reach this goal, NSF and other agencies that fund O/IR astronomy should appreciate all the elements of the U.S. O/IR system and implement policies that guide the system’s development so that federal funding will achieve maximum science and maximum opportunity.

Implicit in this new goal is a changing role for NOAO. The McCray report, A Strategy for Ground-Based Optical and Infrared Astronomy,2 and the AURA-sponsored study on the future of NOAO3 emphasized that to be a more effective component of the U.S. ground-based O/IR system, NOAO must have as its first priority to represent the entire U.S. astronomy community, carrying on activities that benefit all. These activi-

2  

Panel on Ground-Based Optical and Infrared Astronomy, National Research Council. 1995. A Strategy for Ground-Based Optical and Infrared Astronomy (Washington, D.C.: National Academy Press); also known as the McCray report after the panel’s chair, Richard McCray.

3  

Association of Universities for Research in Astronomy, Inc./NOAO. 2000. Building the Future: NOAO Long Range Plan: 2001–2005 (Washington, D.C.: AURA).

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

ties will include providing the scientific leadership and technical expertise needed for building the largest facilities, identifying and providing complementary capabilities that support the suite of large telescopes, and representing U.S. interests in efforts that develop as collaborations, either between public and private institutions or with international partners. In the future, NOAO will probably run unique facilities in preference to nonunique ones; as well, it could play an important, multifaceted role in coordinating the entire suite of U.S. ground-based O/IR facilities.

MAJOR INITIATIVE, PRIORITY ONE: DEVELOP AND BUILD A NEXT-GENERATION GROUND-BASED TELESCOPE (GSMT)

MISSION DESCRIPTION

The panel recommends that highest priority be given to the design of a giant (30-m class) segmented-mirror, AO-equipped, ground-based O/IR telescope (GSMT), with the goal of beginning construction before the end of the decade. The GSMT will be a filled-aperture, diffraction-limited telescope with atmospheric correction by AO down to at least 1 µm. It will achieve order-of-magnitude gains over any extant ground-based O/IR telescope and will provide substantial gains in spatial resolution and near-IR high-resolution spectroscopy even over NGST, for which it will be an essential complement (Figure 2.1). The facility will achieve substantial breakthroughs in the science covered in the NASA Origins theme. Especially in view of the ESO initiative to build even larger, more ambitious ground-based telescopes over a substantially longer timescale than this decade, the successful development of a next-generation ground-based telescope, accessible to all U.S. astronomers and contemporaneous with NGST, is essential for maintaining the tradition of U.S. leadership in astronomy. The ESO proposal for a 100-m-class telescope would offer even more spectacular gains for many kinds of observations, but it is the opinion of the panel that the proposal is too ambitious for the current decade and that an intermediate step, to a 30-m telescope, would be optimal in terms of science, technology, and allocation of resources. Of particular importance, the panel believes, is that a next-generation, ground-based facility be available during the lifetime of NGST.

The GSMT will operate over the wavelength range from 0.3 to

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

FIGURE 2.1 The performance of a 30-m ground-based telescope (GSMT) is compared with that of NGST for point sources for a number of spectral resolutions over a range of wavelengths. The vertical axis is the ratio between the S/N achieved for an observation of a given duration (for an object much fainter than the sky) by GSMT and the S/N achieved by NGST. Diffraction-limited image quality at all wavelengths and an emissivity of 10 percent are assumed for GSMT NGST’s advantage beyond 4 µm is likely to be even greater owing to improvements in detector dark currents and read noise. Superposed is a line showing atmospheric transmission. The comparison shows that GSMT is substantially more effective than NGST in obtaining moderate-to high-resolution spectra of faint compact objects, especially below 2.5 µm. NGST is more effective at longer wavelengths, at wavelengths blocked by the atmosphere, and for observations done at low spectral resolution. It should also be noted that no spectroscopic capability is planned for NGST below 1.0 µm, nor is GSMT expected to deliver diffraction-limited images below 1.0 µm. Courtesy of L.Ramsey, Pennsylvania State University, 1999.

25 µm, with a field of view (FOV) of ~20 arcmin and expected diffraction-limited images over a ~1 arcmin field ranging from ~8 milliarcsec at 1 µm to 0.2 arcsec at 25 µm and with seeing-limited performance of ~0.5 arcsec in the UV. The telescope will provide diffraction-limited performance with AO for λ≥1.0 µm. Its high spatial resolution and powerful spectroscopic capability will be a true quantum leap over any other existing or planned U.S. facility. At the same time, the immense aperture

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

of the telescope will, in and of itself, make the GSMT a uniquely powerful facility for partially corrected or uncorrected observations.4

SCIENCE WITH THE GSMT

The need for very high spatial resolution and moderate to high spectral resolution, with dramatically increased sensitivity, drives the development of GSMT. When steps of the size proposed are taken, it is often the case that the greatest impact will come from discoveries that cannot be predicted—such is the nature of exploration and discovery in astronomy—and that are a major source of the excitement that surrounds a powerful new facility of this kind. Nevertheless, the panel sees many unique opportunities for GSMT to help answer today’s leading scientific questions. Summarized below are a few of the exciting possibilities.

STAR AND PLANET FORMATION

The development of the theory of stellar structure and evolution was one of the greatest achievements of 20th century science. Yet this elegant theory, which explains the life cycle of stars, is incomplete in one critical aspect: it does not predict or account for the formation of stars. Despite its key role in processes as diverse as the origin of planetary systems and the evolution of galaxies, star formation is probably the least-understood aspect of the fundamental processes. Nonetheless, over the last quarter of the 20th century impressive advances in our understanding of star formation came from the continued development of new technological observational capabilities from both the ground and space. During this period astronomers learned the following:

  • Stars form continually in our galaxy within the dense cores of giant molecular clouds.

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In addition to the ESO project, called OWL, there are three other programs in the early planning stages: MAXAT, a 30- to 50-m telescope (New Initiatives Office at NOAO), the 30-m-class CELT (Caltech and the University of California), and ELT, a 25-m scale-up of the HET (Pennsylvania State University and the University of Texas). The GSMT described here corresponds closely with CELT or MAXAT. Although it is too early to judge the future direction of those projects, the panel believes that GSMT could evolve directly from either of them, one from the private, the other from the public sector, or from a joint project created by merging the two.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×
  • The process of star formation is almost always accompanied by the formation of a circumstellar disk. Systems of planets like our own appear to be a natural by-product of the star formation process and are therefore common, as the first observations of extrasolar planets also suggest.

  • Star formation is a complex and dynamic process dominated by gravitational collapse, which is accompanied by the energetic ejection of spectacular bipolar jets and outflows.

  • Stars tend to form in pairs, groups, or clusters but rarely in isolation.

Existing theories cannot simultaneously account for all these facts, and there are additional mysteries—for example, the form of the initial mass function (IMF) and the efficiency of star formation both need to be understood in order to construct a credible theory of star formation. The physical process of star formation spans an enormous range in both spatial scale (about eight orders of magnitude) and density (about 20 orders of magnitude). However, despite the progress of the past two decades, direct observation of the key stages remains a formidable challenge. For example, researchers know little about the crucial processes that occur on relatively small physical scales (less than 200 AU), such as the development of energetic bipolar jets, the growth of a protostar through accretion and infall, and the formation of planets from a circumstellar disk.

The GSMT, working in concert with NGST and the millimeter-wave arrays CARMA and ALMA, will have a profound impact on our understanding of these matters. Probing the 1- to 200-AU scales with a variety of wavelengths will provide a more detailed and comprehensive picture of the earliest stages of star and planet formation than was previously possible. In particular, GSMT will have the angular resolution and sensitivity to study regions as small as 1 AU (at 1 µm) in the nearest protostellar clouds, vastly increasing our knowledge of many phenomena:

  • The origin and nature of bipolar jets. High-angular-and high-spectral-resolution observations should be able to determine how close to the central protostar the jets are collimated and whether jets form as disk winds or are instead driven from close to the stellar surface. Such knowledge could tell us whether such ejections regulate the mass of the star and the form of the IMF.

  • The structure and nature of protostars. High-resolution spectros-

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

copy at near-infrared wavelengths will probe the velocity and density structure of protostellar environments on scales from a few astronomical units down to the stellar surface (even in seeing-limited mode). Protostars gain mass through infall and disk accretion, which are believed to dominate in the inner regions (see Figure 2.2). GSMT observations of the protostellar disk and envelope will show whether material accretes directly from the disk or along dipole field lines from a truncated disk and whether the accretion is steady or episodic. The GSMT’s greater sensitivity will also enable measurement of the photospheric absorption lines from protostellar atmospheres, which are too heavily veiled to be easily detected with smaller telescopes. Such observations will critically constrain the theory of stellar evolution through direct measurements of

FIGURE 2.2 Direct images of the debris disk around the main sequence A star HR 4796 show the advantage of high spatial resolution and the interplay between ground- and space-based facilities. On the left is a mid-IR image (24.5 µm) from the Keck telescope of the thermal emission from the disk. On the right is a near-IR image (1.1 µm) taken with NICMOS aboard the Hubble Space Telescope, which detects the disk in light scattered from the central star. (The large gray disk is due to the coronagraphic mask, which greatly reduces the light of the central star.) With GSMT, much higher resolution images could be obtained of these disks around A stars as well as images of these disks around lower mass and younger stars, which are currently unobtainable. Courtesy of D.Koerner, University of Pennsylvania.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

effective temperatures, surface gravities, rotation rates, and even the accretion energy of protostars.

  • Protostellar companions and masses. High-angular-resolution imaging and spectroscopy will permit measurement of the frequency, separations, and orbital motions of binary companions to protostars and more evolved young stellar objects, such as T Tauri stars, on scales of 1 to 5 AU in the nearest star-forming regions. Such measurements would yield the first direct determinations of protostellar masses, crucial to the development of a complete theory of star formation, and indicate the survivability of protoplanetary disks in multiple-star systems.

  • Disk structure and chemistry. The bulk of the mid-infrared emission from a protoplanetary disk is confined to the inner circumstellar regions with a radius of less than 20 AU. The improvement in angular resolution with GSMT will allow the first spatially resolved mapping of the dust structure and chemistry of young disks in the region where planetary systems are thought to form. For both these disks and the older debris disks (see Figure 2.2), maps of the thermal emission at mid-infrared wavelengths or of scattered light at near-infrared wavelengths could reveal gaps and spiral arms in the surface density caused by gravitational interaction with embedded protoplanets. For instance, Jupiter would have formed a gap of ~1 AU in width in the primitive solar nebula, a feature that would be detectable in GSMT images of the nearest star-formation regions (at a distance of 140 pc).

  • Outer solar system. A more thorough understanding of the early development of our own solar system is needed to interpret observations of extrasolar planetary systems. Near-infrared spectroscopy of KBOs to determine which ices and minerals are present on their surfaces is possible now only for the brightest objects (see Figure 2.3). GSMT spectroscopy will greatly increase the sample so as to cover more of the compounds that could characterize this large population. Also, high-spatial-resolution GSMT images of KBOs will show their sizes and shapes and the homogeneity of their surface compositions, providing constraints on their formation and collisional history. Also, high-spatial-resolution GSMT images of KBOs will begin to resolve their surfaces. Diffraction-limited images at 1 µm with GSMT will provide a spatial resolution of 200 km for an object at 40 AU, corresponding to about 16 resolution elements on the largest known KBOs.

  • Direct planet detection. Simulations indicate that with its current AO system, the Keck telescope could detect reflected starlight from mature Jupiter-sized planets in 10- to 40-AU orbits around six bright stars

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

FIGURE 2.3 Vesta, one of the brightest main belt asteroids, as imaged with the Keck AO system on its second night of operation. Images in three bands (J=1.25 µm, H=1.65 µm, and K′=2.1 µm) were used to produce a true-color image. The open loop (no AO correction) image is shown in the bottom right-hand frame. The top row of images shows the results of deconvolution (i.e., the estimate of the object that, when convolved by the point spread function—shown in the inset— most accurately reproduces the data). In the true-color image, blue represents J; green, H; and red, K. The albedo at 1.2 µm is dominated by the reflection of pyroxene and at 2.1 µm, mostly by that of olivine. Thus, a very blue area shows a concentration of surface pyroxene, and a red one shows a concentration of olivine. Courtesy of R.P.Binzel, Massachusetts Institute of Technology, C.Dumas, NASA Jet Propulsion Laboratory, and the W.M.Keck Observatory Adaptive Optics Team.

within 2 to 4 pc of Earth. The time required to detect a planet scales with the fourth power of the telescope aperture diameter (D), and the minimum separation scales as D, so GSMT will be much more powerful. Young (<10-million-year-old) planets will be detected by GSMT through their thermal emission at 2 µm at separations down to ~5 AU out to distances of ~140 pc.

  • Comparison with brown dwarfs. Detailed spectroscopy of brown

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
×

dwarfs shows that their atmospheres are unlike those of any known star and more like that of Jupiter. Finding extrasolar planets allows us to ask whether all giant planets have similar structures and compositions and how these compare with the properties of brown dwarfs, which are intermediate in mass between giant planets and the coolest stars. The GSMT will be able to characterize atmospheres of extrasolar planets through near-IR spectroscopy.

UNRAVELING THE EPOCH OF GALAXY FORMATION

Within the next decade the panel expects existing 8-m-class telescopes to make substantial progress in assessing the global statistics of galaxies and quasi-stellar objects (QSOs) as a function of look-back time. However, to place these objects in a meaningful cosmological context will require much more demanding physical measurements of small-spatial-scale internal kinematics, chemical abundances and gradients, gas-phase physical conditions, stellar content, and subkiloparsec morphology. These quantities should all be measured as a function of large-scale environment and of look-back time. The observations will be necessary to understand galaxy formation and evolution and how they tie into the development of the large-scale structure of the universe.

Such contextual observations require high angular resolution and sensitivity that cannot be obtained with telescopes of the 8-m-diameter class. The NGST has similar goals in the area of galaxy evolution, but GSMT can both complement and support NGST with its powerful capabilities. The NGST will open up the currently unexplored dawn of the universe—the end of the “dark age” left by the cooling Big Bang—by observing galaxies at z>5. For such objects the most important diagnostic features of the spectra have been redshifted into the thermal IR, where NGST’s extraordinary sensitivity will be unrivaled. However, GSMT will be a powerful tool for studying galaxies with more modest redshifts during the period of cosmic history when most of today’s stars and metals were formed (see Figure 2.4).

To give a specific example, while the measurement of redshifts to z~2.5 to 4.5 is now almost routine, only the very brightest objects can be observed with sufficient spectroscopic precision to delve into the astrophysics. A spectral resolution of R≥5000—higher than what is possible for very faint objects observed with 8-m-class telescopes—is required to resolve, both spatially and in terms of wavelength, the

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.4 Two views of the star formation history of the universe, based on current data. Plotted in each case is the logarithm of the star formation rate (SFR), the rate at which gas in galaxies is turned into stars, per unit volume. In the top panel, this quantity is plotted against redshift. In the bottom panel, the redshifts have been converted to lookback times, given as a fractional age of the universe. Note that the cosmic time before z~5 is relatively brief—NGST will be the crucial facility for exploring this epoch. Over the next decade, large surveys for galaxies in the redshift range 1<z<5, when most of the stars in the present-day universe formed, will be carried out using SIRTF and 4- to 8-m-class ground-based survey telescopes. NGST and 8- to 10-m telescopes will provide follow-up spectroscopy for measuring redshift and determining star formation rates. The GSMT will provide unique access to the chemical and dynamical history of the 1<z<5 universe through its powerful spectroscopic and imaging capabilities. Courtesy of C.Steidel, California Institute of Technology.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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rotation curve or velocity dispersion of a (potentially) low-mass galaxy,5 and the typical half-light radius of such objects at high redshift is only ~0.2 to 0.3 arcsec. Not surprisingly, then, astronomers do not even know such rudimentary information as whether these galaxies are supported by rotation or dispersion. Without the physical measurements allowed by high-dispersion spectroscopy, they are unable to tie one observed epoch to another and are unable to connect theory to observation.

The GSMT will alter this situation dramatically by giving fourfold improvement in (diffraction-limited) resolution as well as a 16-fold gain in light-gathering power, relative to an 8-m-class telescope. Multiobject R= 5000 spectroscopic capability will allow us to establish the relationship between luminosity and mass and to measure the chemical properties of 1<z<5 galaxies through nebular line diagnostics (the rich interstellar absorption line spectrum in the rest-frame UV) and the integrated stellar light. GMST will achieve the same ~50 pc spatial resolution for 1<z< 5 galaxies as ground-based observations of galaxies at the distance of the Virgo cluster. This would place up to ~50 resolution elements across typical compact galaxies at high redshift, thereby converting them from “fuzzballs,” as currently observed, to resolved objects rich in morphological complexity (see Figure 2.5). GSMT spectroscopic determinations will measure the chemical abundances in individual star clusters and giant HII regions and will trace the kinematics of large-scale outflows across the face of each galaxy by observing interstellar absorption lines against the UV continuum from massive stars. These are the essential measurements for understanding the assembly of baryons into galaxies in the early universe.

With such data astronomers will be able to answer the fundamental questions of galaxy evolution: When did galactic bulges form? Are distant galaxies rotationally supported? What controls the decline in the global star formation rate for z<1? What is the mass function (as opposed to the luminosity function) of distant galaxies? How much metal mass is ejected from galaxies during their robust star-forming phase, polluting the intergalactic medium (IGM)? Are chaotic morphologies really indicative of mergers, or are they a natural consequence of rapid star formation? (See Figure 2.6.)

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At this resolution, the terrestrial background in the nonabsorbed bands in the 0.6- to 2.5-µm range approaches the low background accessible from space—the bulk of the background comes from very narrow OH airglow lines and not from thermal emission.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.5 Hubble Space Telescope images, in the rest-frame far-UV and rest-frame optical bandpasses, of one of the brightest known z~3 galaxies. The galaxy has a morphology typical of high-redshift, star-forming galaxies, with a half-light radius of only ~0.25 arcsec, surrounded by more extended and diffuse nebulosity. The core of the galaxy is barely resolved at 1.6 µm with the HST. Higher spatial resolution, such as that of a diffraction-limited GSMT, will be required to resolve such galaxies into individual star-forming knots and to delve into the detailed kinematics that will allow measurements of, for example, dynamical mass, chemical abundance gradients, and the distribution of outflowing metal-enriched gas. Courtesy of C.Steidel, California Institute of Technology, 1999.

Astronomers believe that the diffuse IGM contained more than 90 percent of the baryons during the 2<z<5 epoch. Theoretical models suggest that the Lyman-alpha forest may be a more reliable tracer of the overall matter distribution (because the gas exists in regions close to the mean density of the universe) than galaxies, which are highly biased

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.6 A merger of two galaxies at z=0.831 in a 10 arcsec×10 arcsec patch of the Hubble Deep Field as it would be sampled by an integral field spectrograph, which produces spectra over a two-dimensional format for pixels approximately 0.1 arcsec2. The GSMT will sample such an object with seven times the spatial resolution, corresponding to ~100 pc, the size of a large star-forming region at high redshift. Such a spectrograph would be ideal for GSMT’s study of metal abundance and the kinematics of complex objects at 1<z<4. Courtesy of I.Parry, Institute of Astronomy, Cambridge, United Kingdom, and the Cambridge IR Panoramic Survey Spectrograph group.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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tracers. With R≥30,000 spectroscopy of background QSOs, measurements have been made of the temperature, metal content, and ionization state of the IGM, all on scales of a few kilometers per second. This technique has already produced the most reliable determinations of the cosmic deuterium/hydrogen ratio, the metal content of the diffuse IGM, and the chemical evolution history of high-column-density gas. What is lacking is the three-dimensional information necessary to place the observations into the context of the galaxy distribution at the same cosmic epochs, allowing detailed comparisons with increasingly sophisticated simulations of structure formation. The problem is that QSOs are rare objects—a sufficiently dense sampling requires measuring intergalactic absorption in the spectra of faint galaxies (see Figure 2.7). The GSMT will extend the magnitude limit for high-precision spectroscopy to R~22, increasing the surface density of suitable probes of the high-redshift

FIGURE 2.7 Keck/LRIS spectrum (3.5-Å resolution) of a gravitationally lensed (by a factor of 30 to 40 in apparent luminosity), star-forming galaxy at z~3. In addition to the strong interstellar absorption features, the spectrum is of high enough quality to identify weak stellar photospheric lines from O-stars and to separate the P Cygni profiles from stellar winds for high-ionization features like CIV λ1549 and NV λ1240. An analysis of this spectrum indicates chemical abundances slightly less than solar and a galactic-scale outflow of gas at a velocity of more than 200 km s−1. The GSMT will obtain such measurements routinely for common, unlensed galaxies. Courtesy of C.Steidel, California Institute of Technology.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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universe to an (estimated) 150 deg−2 in the redshift range 2<z<4. This would allow mapping both the galaxy distribution and the diffuse gas distribution over the same cosmological volumes at high redshift, providing for the first time a full accounting of the distribution of baryons. Because of the required high spectral resolution, such crucial observations are beyond the planned capabilities of NGST.

THE STAR FORMATION HISTORY OF NEARBY GALAXIES

Did star formation begin in all galaxies at the same time, and did it proceed from the outside in or inside out? Was it episodic or continuous, and does this depend on galaxy mass or environment? Such fundamental questions are best answered by dissecting stellar populations directly, that is, by determining the age and metal abundances of stars as a function of epoch and position within our galaxy and its neighbors. NGST will probably be able to determine ages for old stellar systems at the distance of M31 (turn-off magnitudes near R=29) in low-surface-brightness regions, but GSMT will resolve the main sequence turnoffs in higher-density regions, to within about 2 kpc of the nucleus of M31 (even closer to the center of M32), and will enable study of stars as faint as the horizontal branch in the halos of galaxies as distant as the Virgo cluster.

Main sequence turnoff photometry is not wholly adequate for high-precision age dating: mean metallicities and elemental abundance ratios (e.g., “alpha” elements) are also required. GSMT’s large aperture and high spatial resolution (assuming a Strehl ratio of 0.3 at 0.7 µm) will enable high-resolution (R=40,000), high-signal-to-noise (S/N>25) spectroscopy of the brightest M31 red giants (with visual magnitude= 21.5) in a single night. By comparing them with synthetic spectra, lower S/N~10 spectra from even shorter exposures (~1 h) would yield accurate mean heavy-element abundances ([m/H] and [α/Fe]).

Elemental abundances in metal-poor stars provide us with new means of chronometry and critical insights into nucleosynthesis from supernovae. The increasing dominance of r-process elements indicates that stars that formed before asymptotic giant branch (AGB) evolution could pollute the interstellar medium (ISM) with s-process elements. By studying the dispersion of these elements in different locations in galactic halos, researchers can learn much about the early history of heavy-element enrichment; for example, very low metallicities coupled with r-process dominance have suggested pollution by only a few supernovae or even just one.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Measurement of r-process patterns and thorium abundances are an entirely new and independent chronometer that provides crucial tests for globular cluster ages derived from stellar evolution models. Furthermore, radioactive dating provides the ages of individual field red giants, which have been identified throughout the halo and the disk and in the Magellanic Clouds. Most of the crucial lines, particularly thorium, are spread out in the violet part of the spectrum, where the ground-based sky is very dark. High resolving power and a high signal-to-noise ratio are essential for such work. With absolute magnitude in U approximately equal to 0.5 mag for almost all metal-poor red giants, ultraviolet seeing-limited observation with GSMT could still measure the age of a field giant as far away as the Magellanic Clouds in less than a night.

SEEING-LIMITED SCIENTIFIC APPLICATIONS

It is important to acknowledge that atmospheric conditions will preclude the AO-corrected operation of GSMT some fraction of the time and that GSMT is not likely to be diffraction-limited below λ=1 µm. Fortunately, there are seeing-limited, wide-field applications for GSMT that will have truly dramatic impact as well. For instance, a giant aperture with a highly multiplexed, wide-field spectroscopic capability could pursue many fundamental astrophysical problems. Because it is often the case that diverse astrophysical processes contribute to general observable trends, fundamental questions must often be approached statistically, with samples large enough to allow separating these contributions. Such problems include the formation and evolution of large-scale structure, of galaxies and the Milky Way, and of stars and their planetary systems. For example,

  • Densely sampled, wide-field spectroscopic surveys with GSMT will explore the evolution of large-scale structure beyond the local universe mapped by the Sloan Digital Sky Survey, i.e., at z>1, allowing astronomers to distinguish among theories of structure formation. At z~1, the 20 arcmin FOV of GSMT corresponds to a co-moving length scale of ~12 h−1Mpc (q0=0.1), which will enable studies of the important 100 h−1Mpc size scale (e.g., as large as the Great Wall and Great Attractor). Redshift surveys at z>5 using Lyman-alpha will map out the clustering evolution of galactic fragments and the genesis of large-scale structure. As discussed above, the absorption spectra of faint background galaxies will

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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map the IGM in the early universe to small scales not accessible with widely separated QSOs.

  • Galaxy formation is a complicated tale, with interwoven story lines of star formation, chemical enrichment, dynamical evolution and merging, and interaction with the environment. To sort out these story lines and the complex relationships between them, it is necessary to trace out galaxy age, star-formation rate, chemical abundance, and morphology as functions of mass and environment over the large redshift range 1<z<5. Considering this large parameter space, the relative rarity of populating some bins (for example, very metal-poor starbursts), and the need to obtain meaningful statistics in all categories, it is likely that very large samples, including perhaps many hundreds of thousand galaxies, will be required. Obtaining spectroscopic samples this large over scales of many degrees is a feasible goal for GSMT.

  • The formation and evolution of the Milky Way and other local group galaxies can be discerned from the detailed record of the age, kinematics, and chemical abundances of individual stars. To recover this record requires the study of abundant populations—dwarf stars, for example; studies of millions of stars can be used to discover the mean trends, such as age versus kinematics. Combining this information with galaxy substructure will inform such important matters as the merging history of galaxies. Its multiobject spectroscopic capability will make GSMT a powerful tool for such work. The GSMT could even investigate the merger history in the Virgo cluster, by tracing the positions and properties of intracluster red giant stars (with a typical magnitude of ~28).

THEORY CHALLENGE FOR GSMT

A theory challenge for GSMT is to develop models of star and planet formation, concentrating on the long-term dynamical coevolution of disks, infalling interstellar material, and outflowing winds and jets, as described in the report of the Panel on Theory, Computation, and Data Exploration (Chapter 6).

TECHNOLOGY BASIS

The success of the segmented Keck 10-m telescopes has provided astronomers with the technology to build increasingly large telescopes without incurring the risks associated with increasing the size of mono-

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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lithic mirrors. For the first time, they have a scalable technology to apply for ever-larger telescopes.

Other key advances in computational engineering design and analysis and in the active control of optics (as exemplified by Gemini and Keck) allow predicting with confidence the performance of future large telescopes by integrated modeling of their optical, mechanical, and thermal properties. This capability has greatly reduced the risk inherent in designing and building larger telescopes.

Adaptive optics, a key component of a future very-large-aperture telescope, progressed significantly in the 1990s. AO systems now exist or are being built for all of the world’s largest telescopes, and their scientific productivity is rapidly increasing. Even so, the challenges of developing AO are enormous, and existing and planned AO systems fall far short of the ideal. Therefore, the further development of AO technology for GSMT will also directly improve the performance of AO systems on 8-m-class telescopes.

The next section reviews other technology issues that affect the cost of building the GSMT.

KEY TECHNOLOGY ISSUES

The GSMT, along with the development of AO, will cost an estimated $400 million, most of it to be spent in the current decade. The panel proposes that this facility be built and operated using a combination of federal, state, and private funds, making it a collaborative effort between national and independent observatories. It also proposes that NSF be prepared to pay at least half of the total capital and operating costs, with the balance to come from private observatories and/or foreign partnerships. The costs of telescope development should be about $3 million per year for at least 3 years, ramping up to cover the construction costs as soon as the technology is ready. This should allow time to study the various fabrication trade-offs and mirror support issues, as well as to develop the basic telescope design and cost. The panel believes that the AO effort associated with the development of GSMT should be funded at $5 million per year for the next 10 years. This level of funding should be sufficient to support national, university, and industry efforts with respect to a number of key AO issues, including the following:

  • Better wavefront sensors (faster, with lower read noise, more pixels, and improved IR response);

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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  • Improved laser beacons (more affordable, powerful, and reliable; better coupling to the Na layer; ability to make multiple beacons);

  • More capable deformable mirrors (more affordable and more reliable; more stroke, more degrees of freedom, and a wider choice of actuator spacing);

  • Better understanding of multiconjugate adaptive optics through modeling, simulations, and experiments;

  • Advanced techniques and algorithms for achieving the needed computing speed;

  • Study of various hybrid systems using both natural and laser guide stars; and

  • New, more efficient wavefront sensing approaches (ideas, simulations, and experiments).

The utility of a 30-m or larger aperture telescope depends crucially on its near-diffraction-limited performance, particularly in the 1- to 25-µm wavelength range. Because of the sky background faced by ground-based telescopes, truly spectacular gains are possible for unresolved sources when the effective sampling scales as the diffraction limit. Also, the general transparency and width of the atmospheric windows are strongly limited by precipitable water, arguing further for placing the GSMT at a superb site, with low water vapor included along with the usual criteria of excellent seeing and a high fraction of workable nights. Furthermore, since instrumentation for these large telescopes will be vastly simpler only if diffraction-limited performance is achieved, AO is essential to justify the large investment required. The difficulties associated with AO grow rapidly with the number of controlled degrees of freedom (dof), and the largest astronomical AO systems currently have about 350 dof. For a 30-m aperture to achieve a Strehl ratio of 0.5 at 1 µm requires control of ~7000 dof. This level of control will require significant improvements in wavefront sensors, deformable mirrors, laser beacons for artificial stars, and computational speed, as well as improved theoretical models and simulations. In addition, the problem of correcting for the atmospheric distortion of the wavefront using artificial guide stars must be generalized to the multiple-guide-star case to achieve adequate correction over significant fields of view. Fortunately, the use of multiple guide stars will provide diffraction-limited images over fields of view greater than about 1 arcmin. The AO development work will also greatly help existing large telescopes by providing superior AO

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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systems for them, allowing them to work at the diffraction limit at shorter wavelengths and thereby greatly increasing their scientific power.

It is interesting that as the telescope grows in size, the potential for tomographic measurements of the atmosphere with natural guide stars grows as well.6 Nevertheless, the panel believes that multiple laser beacons offer a more convenient and predictable means for tomographic measurement of the atmosphere. Both approaches need to be thoroughly explored.

COST ISSUES

This chapter aims not to justify a specific design for GSMT but to point out that enough work is now under way to inspire confidence that a serious investment in technology development will bring about the necessary innovations. This is the context for the following remarks on cost issues.

To make the next-generation telescope cost-effective, significant engineering improvements are clearly required. Empirical studies have shown that the cost of a telescope scales roughly with aperture as D2.6. The Keck II telescope cost of approximately $80 million suggests that without further innovation, a 30-m aperture would cost roughly $1.4 billion. The experience of designing and building Gemini and Keck has shown numerous opportunities for engineering innovations and development that will significantly reduce costs.

Breaking the cost curve, as the developers of the present generation of 8-m-class telescopes were able to do, is an essential part of this endeavor. In scaling up from 4-m-class telescopes, Gemini and Keck broke the cost curve by factors of 4 to 8. Clearly, then, the astronomy community has experience and success with this kind of challenge. For GSMT, costs must be reduced by roughly a factor of 4.

In comparison, to build the much more powerful ESO 100-m OWL (the acronym can be taken to stand for either Overwhelmingly Large Telescope or Observatory at a World Level) for $1.5 billion will require

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This has been an argument for building a 100-m telescope. However, although it eliminates the need for the laser itself, atmospheric tomography is just as challenging for natural guide stars, and the number of degrees of freedom needed for a given correction continues to rise as the square of the aperture, that is, by a factor of about 10 for a 100-m telescope over a 30-m telescope.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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innovation that reduces costs relative to Keck by a factor of 20. Such a cost reduction is significantly more challenging and does not appear to be reasonable for a single engineering step. In fact, if OWL could be built for this price, the same technology could produce a 30-m telescope for $65 million, which would be an even more compelling next step. The panel is excited about the possibility of OWL but expects that it will probably take much more time to be developed than GSMT.

To meet the 2010 goal, development work on GSMT technologies and strategies for cost savings should begin immediately. Much of the needed human expertise is already available or will shortly be, when the current generation of 8-m-class telescopes will have been completed, so the timing is excellent. Here the panel gives a few examples of ideas that could bring about the necessary cost savings. In modern telescopes, optics and the related support and control systems account for 30 to 50 percent of the cost of the entire project. This amount includes the cost of materials, polishing, passive support systems, and active control systems. In each of these areas, the panel sees great opportunities for cost savings. For example, segment size is a key cost driver: gravity-driven deflections of mirror segments are a major difficulty, one that increases as the fourth power of the radius of the segment. Smaller segments will therefore allow much thinner segments as well as simpler passive supports. Specifically, in modest-sized pieces (~1m), Zerodur (the material used for Keck) costs about $100 per kilogram. Accordingly, thinning the segments can produce significant cost savings. In addition, polishing costs for Keek-style segments (off-axis sections of a hyperboloid) depend on the asphericity, which scales as the square of segment size, so smaller segments allow for more economical polishing methods. The polishing of spheres using planetary polishers (with which multiple mirrors are polished simultaneously) for segments for the Hobby-Eberly telescope turned out to be extremely economical. The asphericity of GSMT’s 1-m segments will be only 10 percent of that of Keck segments. A variant of stressed mirror polishing may allow GSMT segments to be warped and polished as spheres with planetary polishers, which would dramatically reduce polishing costs.7

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Optical fabricators are presently claiming $15,000 per square meter for polishing and testing spheres by this technique. Another option for reducing the optical costs may be to pursue a semistationary spherical primary mirror, along the lines of the Hobby-Eberly telescope. Such a design requires compromises in performance but greatly reduces cost compared with fully steerable Ritchey-Chrétien telescopes.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Active control of the telescope mirror segments will be required. Because the segments are smaller, there will be many more than the 36 in Keck. For this reason, control system innovation is essential. Fortunately, the general trend of technology with time is toward higher-performance electronic devices that are also more compact and more affordable. The Keck telescopes use interlocking-edge sensors that are relatively expensive and awkward to service. Schemes to make sensors that are basically films on the segment edges may lead to order-of-magnitude reductions in cost and greatly simplify segment servicing (e.g., recoating).

It is likely that a weatherproof covering will be needed for GSMT. A dome provides protection from both weather and wind, easing many environmental constraints. Traditionally, domes are rather expensive, but large stationary and movable geodesic structures such as those used for modern sports stadiums may suggest a technique for greatly reducing the cost of the enclosure.

CONTEXT ISSUES

It is expected that NOAO, restructured to form a strong national organization, as described in a previous section of this chapter, will play a prominent role in the development of the GSMT. This project obviously will offer a splendid opportunity for public-private partnering that could lead to a common understanding and advancement of the system. Regardless of other efforts inside or outside the United States, NOAO should initiate a solid program on behalf of (and involving) the astronomy community to explore the scientific drivers and technical hurdles associated with the GSMT. This effort will position the community for strong and effective participation. The panel can imagine a range of possible roles for NOAO in building and operating the GSMT, from leading the construction of GSMT if the program is carried out mostly with federal funds to simply forming a strong U.S. presence in a collaboration with independent observatories and/or international partners if the program is carried out with mostly nonfederal funds. For developing an O/IR ground-based system, the panel recommends one particular alternative—NOAO partnering with one or several independent observatories to build and operate GSMT—as the most desirable course. For all of the alternatives, the observing time available to the U.S. astronomy community, an amount proportional to the investment by NSF, could be distributed by NOAO (as is being done for the WIYN telescope).

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Considering the difficulties in fighting gravity and wind loading, as well as the costs of enclosures to shelter a ground-based telescope, it is likely that at some point it will become more cost-effective to build a very-large-aperture space-based telescope than to build a ground-based telescope with the same aperture. From the present vantage point, GSMT is arguably on the traditional side of that comparison, according to which space-based telescopes are more expensive, but if NGST succeeds in achieving the 8-m size for its proposed budget, then ground-based telescopes with apertures larger than about twice that of GSMT may be approaching this crossover point. Experience with the GSMT and NGST technologies will help to determine whether even larger ground-based telescopes, for example, the proposed 100-m OWL telescope, will be more cost-effective than space telescopes.

ANCILLARY BENEFITS

A 30-m telescope with its superb angular resolution and sensitivity may be the preferred way to follow up extremely faint sources associated with x-ray, gamma-ray, and microjansky radio sources, particularly if more than merely a redshift is desired. Should NGST not be achieved, GSMT’s existence becomes an absolute necessity for progress in the fields described above.

MAJOR INITIATIVE, PRIORITY TWO: A LARGE-APERTURE SYNOPTIC SURVEY TELESCOPE (LSST)

MISSION DESCRIPTION

The panel advocates the construction of a Large-Aperture Synoptic Survey Telescope (LSST) with the ability to map the entire accessible sky to 24th magnitude (in one optical band) over the course of three nights. (This is about a magnitude deeper than the Sun would appear at the distance of the Magellanic Clouds or the Milky Way galaxy would appear at z=1.) The science objectives, which range from solar system science to cosmology, can be addressed simultaneously with the same set of images. For the first time, astronomers and the general public would have access to a motion picture of the night sky.

The requirements for the proposed system follow from the expression

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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for signal-to-noise ratio in a sky-dominated exposure, yielding a figure of merit that scales as AΩ/σ2, where A is the system’s effective aperture, Ω is the field of view of the focal plane, and σ is the seeing. To map out the 20,000 deg2 of accessible sky down to 24th magnitude every few nights will require the equivalent of a 3-deg field of view on a 6.5-m-aperture telescope (one concept is shown in Figure 2.8).

The detectors of choice for the temporal monitoring task would be thinned charge-coupled devices (CCDs); the requisite extrapolation from existing systems appears to constitute only a small technological risk. An IR capability of comparably wide field would be considerably more challenging but could evolve as a second phase of the telescope’s operation. Instrumentation for LSST would be an ideal way to involve independent observatories with this basically public facility.

SCIENCE WITH LSST: THE WIDE AREA VARIABILITY EXPERIMENT

The unprecedented capabilities of LSST open up the possibility of a new kind of science program, a wide area variability experiment (WAVE), whereby one or a few simple survey modes can simultaneously address a number of frontline science questions.

NEAR-EARTH OBJECTS

The orbits of many asteroids intersect the orbit of Earth. These so-called near-Earth objects (NEOs) present a threat to life on our planet, with effects ranging from the local damage inflicted by smaller members of the NEO population (for example, the blast-wave destruction of 1000 km2 of Siberian forest at Tunguska in 1908) to global disruption of the biosphere (as occurred with the impact of a 10 km body in the Cretaceous-Tertiary event).

Extrapolations from recent surveys suggest that some 1000 NEOs are larger than 1 km in diameter (see Figure 2.9) and as many as 105 to 106 NEOs have a diameter of 100 m or more. The vast majority of these objects has yet to be discovered, but a statistical analysis indicates a 1 percent probability of impact by a 300-m body in the next 100 years. Such an object would deliver 1000 MT of energy and (assuming an average of 10 people per km2 on Earth) result in 100,000 fatalities. The damage caused by an impact near a city or into a coastal ocean would be orders of magnitude higher. Of course, the distribution is extremely

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.8 Optical ray trace for one concept of LSST. This design results in a 3-deg-diameter FOV at f/1.25. Excellent image quality is achieved at wavelengths from 0.3 to 2.2 µm, and the system can be fully baffled for either optical or IR imaging. The diagram shows how very large secondary and tertiary optics are required to achieve such a large field, a significant increase in difficulty over present-generation large telescopes. Courtesy of R.Angel, University of Arizona. (This figure first appeared in a paper by R.Angel et al. in Imaging the Universe in Three Dimensions: Astrophysics with Advanced Multi-Wavelength Imaging Devices, Proceedings from the Astronomical Society of the Pacific Conference Vol. 195, edited by W.van Breugel and J.Bland-Hawthorn, 2000, p. 81; reproduced by permission of the Astronomical Society of the Pacific.)

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.9 Orbits for 100 representative near-Earth objects with estimated diameters of 1 km or more; they represent only about 5 percent of the total estimated population in this size range. All orbits included have perihelion distances of 1.10 AU or less, and the orbits have been projected into the Earth-Sun (ecliptic) plane. Also shown by black dashed lines are orbits for the terrestrial planets Mercury through Mars; the positions of the planets on January 1, 1997, are also indicated by dark purple circles. The vernal equinox is to the right. Courtesy of R.P.Binzel, Massachusetts Institute of Technology.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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non-Gaussian: the majority of impacts would have a far smaller effect and a small fraction would have a catastrophic result. Nonetheless, such an impact clearly constitutes an extreme example of the influence of the astronomical environment on Earth.

The reality of the impact threat has been recognized by scientists only in the last 20 years. In the past few years, thanks to several reported near-miss encounters with small objects, it has become a subject of intense interest to the general public and has even been discussed in the U.S. Congress. Although it can be argued that other threats to life on Earth pose risks exceeding that of an asteroid or comet impact, the public feels clearly that any significant risk that is avoidable deserves attention. The contribution of astronomers to this task is to find these objects sufficiently far in advance (decades) that countermeasures could be taken.

A survey for NEOs demands an exacting observational strategy. To locate NEOs as small as 300 m demands a survey down to 24th magnitude, a capability five magnitudes beyond that of existing survey telescopes but well matched to LSST. NEOs spend only a small fraction of each orbit in the vicinity of Earth. Repeated observations over 10 years would be required to explore the full volume of space occupied by these objects. During this time, LSST would discover NEOs at the rate of about 100 per night and obtain astrometric information on the much larger (and growing) number of NEOs that it had already discovered. Precision astrometry is needed to determine the orbital parameters of the NEOs and to assign a hazard assessment to each object. Astrometry at weekly intervals would ensure against losing track of these fast-moving objects in the months and years after discovery.

KUIPER BELT OBJECTS

Kuiper Belt objects (KBOs) are the most primitive bodies in the solar system. Because their orbital dynamics and compositions carry an imprint of the formation of the solar system, they are arguably the most important missing piece in efforts to understand the formation process. For example, astronomers already have evidence for the injection of comets from the Kuiper Belt and for the ejection of matter to the Oort Cloud and to the interstellar medium. It would also be important to model the collisions between KBOs, which generate a dust ring around the Sun that is a local analogue of the dust rings discovered recently around nearby main-sequence stars.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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KBOs are among the most challenging objects in the solar system to discover and study. A deep census with LSST is needed to establish the orbital and gross physical properties of 10,000 KBOs; such a large sample would be needed to model the complex dynamical structure of the Kuiper Belt. For example, many KBOs occupy mean-motion resonances with Neptune (as does Pluto). Dynamical models of the early solar system suggest that the relative populations of different resonances can be used to measure the rate and total distance of Neptune’s migration, which is itself a measure of the mass ejected outward by Neptune toward the Oort Cloud. However, with samples as small as the one composed of the 60 KBOs with known orbits, a majority of the resonances appear empty and population ratios cannot be accurately determined.

The science requirement to accumulate 10,000 KBOs is an independent constraint for the design and operation of LSST. The luminosity function of the KBOs shows that about 10,000 such objects brighter than red 24th magnitude are to be found in the whole sky. The survey must therefore cover the whole sky in a band centered on the ecliptic and extending ± 30 deg from it to red 24th magnitude. The coverage must be repeated at intervals weekly or monthly near discovery, dropping to yearly once the orbits have been approximately determined. The panel estimates that all 10,000 KBOs could be discovered within 1 year on LSST. Subsequent astrometric observations for orbit refinement would take up a quickly diminishing fraction of the time in succeeding years. The KBO survey would operate concurrently with the NEO survey described above.

SEARCHING FOR OTHER PLANETARY SYSTEMS

Two techniques will be used to search for other planetary systems: occultations and microlensing. A typical gas giant planet (a degenerate hydrogen body with a radius fixed near 108 m) has a cross section of about 1 percent of a solar mass main-sequence star (with a radius of about 109 m). In the occultation technique, stars will be monitored with subpercent photometric precision to search for the periodic dimming as a companion planet crosses the face of the star (for those orbits aligned with the line of sight). Assuming random distribution of orbital planes produces an occultation probability per planet-bearing star on the order of 10−3. If, as Doppler velocity measurements suggest, 1 star in 20 possesses a close-in gas giant planet, then the probability of detecting a planet by occultation is on the order of 5×10−5 per star. Because accu-

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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rate photometry of ~108 stars is completely feasible with LSST, repeat measurements at intervals shorter than the orbital period should detect some 5000 gas giant planets. Such a large sample would have great value: for example, the incidence of planets could be determined as a function of stellar spectral type (mass).

By exploiting the remarkable phenomenon of gravitational microlensing of distant stars, intensive monitoring can be used to search for planets with masses as small as that of Earth. The essential requirement is that the apparent planet-star separation be comparable to the Einstein radius. This requirement is not especially stringent. For example, if our own solar system were to be observed in this way (from a location 10 kpc distant against a lens 5 kpc away), a signal from Jupiter would be found in almost 20 percent of solar microlensing events.

The planet-search program imposes two requirements on LSST. First, LSST must generate photometry accurate to a few tenths of a percent. This is a modest requirement even for stars at 20th magnitude, given the quality of modern CCDs and the large aperture of the LSST. Second, each star must be reobserved at intervals comparable to or less than the crossing time (about 1 day for both the occultation and microlensing methods). It is probable that planet-search observations could be conducted using the same survey data obtained for the NEO and KBO surveys.

OBSERVATIONAL COSMOLOGY WITH SUPERNOVAE

Type Ia supernovae have been demonstrated to be excellent distance indicators. A program of repeated scans of the sky will detect about 100,000 supernovae per year. The nearby ones can be used to trace out departures from smooth Hubble flow caused by the nonuniform distribution of dark matter. More distant supernovae found by LSST (followed up with deeper imaging on other large ground- and space-based telescopes) will complement studies of the small-scale anisotropy of the microwave background that also measure cosmological parameters such as the density of matter and dark energy. Distant supernovae are also a powerful probe of the history of star formation over cosmic time.

STUDIES OF ASTROPHYSICAL VARIABILITY

The resulting archive of stellar variability would be a fundamental resource for studies of stellar astrophysics. The discovery of large num-

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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bers of eclipsing binaries with a broad range of masses and chemical compositions would provide fundamental data such as masses and radii for comparison with models. Temporal data for extragalactic objects, particularly AGN and lensed quasars, are powerful probes of the nature of the extreme environments surrounding massive black holes.

DETECTION OF RARE TRANSIENT OBJECTS

Mapping the entire accessible sky to 24th magnitude will open up a vast new discovery space. Optical counterparts of gamma-ray bursts are one example of unanticipated phenomena that reside in the time domain, but there are surely others. It has been suggested that some of these events become very bright (~8th magnitude) for short periods of time. If so, and if they can be detected rapidly enough, these optical transients will serve as powerful probes of the intergalactic medium, surpassing in distance and detail what can be done with quasars.

WHITE DWARFS IN THE GALACTIC HALO

Imaging of large areas at high galactic latitude repeated over a period of years using optical (VRI) colors will uncover, through their proper motions, a complete sample of halo white dwarfs. If, as the MACHO microlensing experiment suggests, an important component of the galactic halo is stellar mass objects of ~0.5 solar masses, the best candidate is a population of very old, very cool, low-luminosity white dwarfs. A deep survey at VRI colors would have the best chance of detecting both those with hydrogen-rich (and infrared H2-dipole opacity-dominated) atmospheres and those with helium-rich atmospheres.

A DEEP DIGITAL MAP OF THE SKY

By coadding repeated scans of the sky, LSST will produce digital composite images of unprecedented depth. For example, in the course of a year, combined images with a depth 2.5 magnitudes fainter than a single image will be produced, corresponding to a limiting magnitude of 26.5. With these will be generated well-populated catalogs of rare and unusual objects for spectroscopic study by the 8-m generation of telescopes. The spatially coherent distortions of the images of faint, distant galaxies will be used to map out the structure of foreground mass concentrations, using the signature of weak gravitational lensing. Such wide-

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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area, deep images can also be used to search for faint objects such as ultralow-surface-brightness galaxies.

A DEEP INFRARED MAP OF THE SKY

With very modest integration times, a sufficiently large infrared detector array (beyond current feasibility) could be used to generate a map of the sky that is 100 times (5 magnitudes) deeper than the Two Micron All Sky Survey (2MASS) data set. This would fill the gap between the existing data and the IR limits of the current generation of large-aperture telescopes. For example, an all-sky survey to J, H, K~20 would reach deep enough to detect what may be the majority population of field brown dwarfs in the immediate solar neighborhood. Recent simulations suggest that many local constituents are expected to have temperatures much below 1000 K; as mentioned, these could be too faint for the ongoing 2MASS and Sloan Digital Sky Survey (SDSS) surveys and too rare per unit surface area for infrared surveys covering limited regions of the sky.

THEORY CHALLENGE FOR LSST

A theory challenge for LSST is to understand the origin, relationships, and fate of small bodies in the solar system, as described in the report of the Panel on Theory, Computation, and Data Exploration (Chapter 6).

Historically, the solar system has provided us with nature’s most revealing dynamics laboratory. Newton formulated his laws of gravitation largely to explain new measurements of the motions of the Moon and planets. More recently, the importance of dynamical chaos was first discovered in the solar system by astronomers studying the orbits of asteroids. The new LSST observations of vast numbers of solar system and other objects promise new material from which exciting developments in theory are to be expected.

DATA FLOW AND INFORMATION DISTRIBUTION

The LSST with WAVE is an ambitious program: it will be a pathbreaking undertaking, providing unequaled opportunities for developing real-time data-mining tools and techniques and for testing the scaling properties of database structures and algorithms.

Because the endeavor is so challenging, it is important to recognize

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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that it builds on current successes in high-data-rate projects in optical astronomy and derives great benefit from advances in computing. The increasing availability of cost-effective computing and mass storage hardware is outstripping the increase in the rates of data produced by even the most ambitious astronomical instruments. For example, the increase by a factor of 100 in the data rate from present microlensing surveys (initiated in the late 1980s), which produce 5 to 10 gigabytes (GB) of raw image data per night, to the ~1 terabyte (TB) per night rate expected for the WAVE project (starting in the middle of the current decade) will be more than offset by advances in computing and mass storage.

Hardware is only part of the solution to the data processing problem, of course. The software must (1) process the data stream in near real time, (2) detect and classify variable and moving objects, and (3) place the results in a readily accessible data repository. Considerable experience has already been gained in these tasks from microlensing surveys, and the SDSS and 2MASS are adding a wealth of new software that can be applied, both conceptually and specifically, to future projects.

An example of a step in the data reduction process is the detection of variable objects. Experience from the microlensing surveys suggests that perhaps 1 object in 1000 will exhibit statistically significant variability. Given 10 billion objects in the sky within the range of LSST, a catalog of ~10 million variable astronomical sources will be generated. It seems clear that this new view will have a profound impact on astronomy and astrophysics in studies of objects ranging from quasars and AGN to gamma-ray bursters, supernovae, variable stars, planets, comets, and asteroids. General-purpose image analysis tools keyed to variability are already in the final stages of development. These routines exploit the recent progress made in supernova and microlensing search projects. By automatically scaling and transforming two images so that an accurate subtraction can be performed, the separation of variable objects from more plentiful nonvariables becomes straightforward. To date, the classification of detected variability (into solar system objects, supernovae, microlensing, and so on) has been done by humans. Several research groups are currently devising a machine-assisted way to carry this classification out. The panel notes that the development of these tools is a prime example of a cross-disciplinary activity mutually beneficial to both the computer science and astrophysics communities and one that NSF should be eager to support.

Implementing an effective database and user interface for large

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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volumes of astronomical data is a challenge that should be addressed by the National Virtual Observatory (NVO) initiative. The NVO will add great leverage to the WAVE data set, which will contribute the temporal dimension to the aggregate data set, while taking full advantage of unified data structures and user interface developments. The WAVE database will by itself likely be the largest nonproprietary data set in the world—it will be an ideal resource for testing the scaling and efficiency of data-mining tools and techniques.

A considerable effort will be required to construct a system producing roughly a terabyte of raw data per night, with rapid data reduction of images, classification of variability, characterization of sources, and rapid distribution of the data. The panel emphasizes that it is crucial to consider LSST with WAVE as precisely that: a complex system for which the telescope and instrumentation are only the front end.

MULTIPLICATIVE ADVANTAGES AND DISCOVERY SPACE POTENTIAL

One of the most attractive aspects of LSST is that it will enable simultaneous pursuit of many of the science goals described above. The time domain is (with a few notable exceptions) largely unexplored in astronomy. WAVE will provide unprecedented access to the theater of the sky and will pay tremendous dividends for a wide variety of scientific objectives beyond the ones mentioned here. The benefit of a continuous, deep, O/IR sky survey to future space missions and ground-based radio astronomy should be considerable. The technology for the construction of the optics and instruments is well in hand, and the project could lead the way in applying state-of-the-art information technology to achieve the rapid distribution of useful data to both the scientific and lay communities.

TECHNOLOGY AND COST ISSUES

TELESCOPE AND INSTRUMENTATION

Based on the existing successful projects of this size and allowing for a more complex optical system, the panel estimates the construction cost of a 6.5-m telescope with a 3-deg FOV at $60 million. The state of the art in currently deployed mosaic CCD arrays is 10K×12K pixels. Cameras of 18K×18K are currently in development, and there is no fundamental

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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impediment to achieving the roughly 30K×30K pixel array that would be required to cover the 3 deg×3 deg FOV of LSST. Paving the field of LSST at 0.3 arcsec/pixel with existing 2K×4K CCDs would require 162 devices, at a detector cost of roughly $6 million. Optics, mounting, cryogenics, electronics, and system integration would add ~$10 million, for a total instrumentation cost of $16 million.

A second-generation instrument with IR detectors is an obvious next step for the system and would greatly benefit from further developments in the footprint of IR arrays.

DATA PROCESSING AND DISTRIBUTION PIPELINE

Current high-end workstations with 250 GB of disk space, a few gigabytes of memory, and multiple processors cost approximately $20,000. Real-time analysis will require roughly 10 TB of disk space and the equivalent of perhaps 50 current high-end workstations. At current prices this analysis system would cost approximately $1 million, but the cost for this level of performance continues to fall steadily with time.

The estimation of software costs is less certain. Based on experience gained with SDSS and 2MASS and the current state of the art in variability analysis, implementing the WAVE analysis system should require approximately 30 full-time-equivalent (FTE) years of programming effort, at a cost of $3 million. Developing the requisite data structures and a user interface will require a comparable effort also costing about $3 million, for a total software capitalization cost of $6 million. Maintenance and upgrades should be budgeted at an annual cost of 10 percent of the initial software investment, or 6 FTEs, for a cost of $3 million for 5 years of operation.

The data repository costs will depend on the degree of synergy with the National Virtual Observatory and the amount of user support provided. Based on experience gleaned from the microlensing projects, the panel estimates that the volume of reduced data will be roughly one-tenth the volume of the raw image data. Such a time-series database would grow at a rate of roughly 20 TB per year and would, ideally, be stored on magnetic disks, at a cost of roughly $5 million per year if implemented at current prices.

The costs of the LSST are projected to be $83 million for capital construction and $42 million for data processing and distribution for 5 years of WAVE operation, for a total cost of $125 million. Routine

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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operating costs, including a technical and support staff of 20 people, are estimated at approximately $3 million per year.8

CONTEXT ISSUES

Both the construction and operation of LSST and the processing and distribution of the data present suitable opportunities for NOAO to provide a critical service to the community, in keeping with its new role.

It is clear that this type of facility and the database that it will produce represent a critical element of ground-based support for space missions. Furthermore, they would form an integral piece of the proposed National Virtual Observatory—a multiwavelength assemblage of archives from many space- and ground-based observatories with the tools to exploit the total dataset. The project will generate ~1 TB of data every night that will have to be reduced in near real time. The classification of variable sources is an interesting and challenging computational problem that is amenable to neural network and adaptive techniques. The project would produce the world’s largest nonproprietary dataset, which could serve as a testbed and development platform for investigating scalability in database implementations, including access/query issues, and for exploring data mining as a tool for research.

ANCILLARY BENEFITS

The panel believes that significant educational and societal benefits will accrue from the LSST. When maps of the changing sky become readily accessible on the Web, the general public will for the first time have access to images of such phenomena as moving objects detected in the solar system and stars exploding in the distant universe. Astronomical imagery will offer time-lapse movies in addition to still photos. A motion picture of the sky should be a qualitatively new tool for K-12 education: imagine a teacher having the class track the motions of the planets on a

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The cost estimated by the Astronomy and Astrophysics Survey Committee included the $83 million capital construction cost and $57 million for all operations, including data analysis, and added 15 percent of the capital cost for instrumentation and 15 percent for grants, for a rounded total of $170 million (see Astronomy and Astrophysics Survey Committee, National Research Council. 2001. Astronomy and Astrophysics in the New Millennium, Washington, D.C.: National Academy Press).

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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weekly basis, follow the approach of an incoming comet, or comb the database for galaxies with recent supernovae or cataclysmic variable stars. In addition, the astronomy community will continue to search for objects in the solar system that pose a threat to life on Earth.

MODERATE INITIATIVE, PRIORITY ONE: TELESCOPE SYSTEM INSTRUMENTATION PROGRAM: LEVERAGING NONFEDERAL INVESTMENT AND INCREASING PUBLIC ACCESS

The U.S. ground-based astronomy inventory consists of nine 6.5- to 10-m-class telescopes (operating or under construction), nine 2.5- to 5-m telescopes, and numerous smaller instruments. Considered together, this collection of both national and independent observatory facilities represents the world’s most powerful ground-based telescope arsenal, with unequaled opportunities for maintaining leadership in research. However, these facilities have traditionally not worked together as a coherent system, in contrast with astronomy facilities abroad, which are dominated by national or international observatories. The panel believes that better coordination and cooperation are essential to realizing the full potential of this system and that NSF should work to achieve such coordination and to ensure that facilities and data are made widely available to the entire astronomy community.

DEFINITION

The panel proposes a new program, the Telescope System Instrumentation Program (TSIP), modeled on the Facilities Instrumentation Program9 of support for instrumentation and instrumentalists at the independent observatories. The TSIP would guide the evolution of the telescope system so that it becomes more powerful and more diverse; it would do this by, for example, favoring instruments with unique capabili-

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Panel on Ground-Based Optical and Infrared Astronomy, National Research Council. 1995. A Strategy for Ground-Based Optical and Infrared Astronomy (Washington, D.C.: National Academy Press); also known as the McCray report after the panel’s chair, Richard McCray.

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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ties and those that would be particularly effective in reaching the scientific goals described here. The panel supports the twin goals of achieving greater public access to these facilities and encouraging and leveraging the contribution of institutions that contribute nonfederal funds to the U.S. astronomy enterprise, to be accomplished by equal funding for both goals.

SCIENCE DRIVERS FOR 8-M TELESCOPES WITH ADVANCED INSTRUMENTATION

With the new generation of 8-m-class, ground-based O/IR telescopes and state-of-the-art instrumentation, many of astronomy’s primary science goals for the next two decades can be achieved. Some examples follow:

  • Assemble very large samples of galaxy photometry and spectroscopy over the redshift range 0<z<2 to measure the chemical and, to the extent possible, structural evolution of galaxies in the context of the growth of large-scale structure. This effort will require wide-field imaging and highly multiplexed moderate-resolution (R~5000) spectroscopy. Instrumentation required: moderate-resolution, low-background spectrographs with multi-million-pixel, low-noise, near-IR array detectors.

  • Identify, through low-resolution spectroscopy, distant supernovae found through large-area surveys. Use type Ia supernovae in the redshift range 0<z<1.5 to measure cosmological parameters, particularly to confirm recent measurements of a nonzero cosmological constant. Compile observations of all supernovae to study the history of star formation rates over a range of galaxy types and luminosities (see Figure 2.10). Instrumentation required: high-sensitivity optical and near-IR, low- to moderate-resolution spectrographs fed by AO systems.

  • Probe the stellar content of the Galactic halo to characterize its assembly and chemical enrichment history. Find thousands of blue horizontal branch stars and RR Lyraes in the Galactic halo and obtain medium-resolution spectroscopy to map the dark halo to 200 kpc. Search for extremely metal-poor stars and other subpopulations and measure their kinematics (three-dimensional motions) to reveal how the halo was assembled through early agglomeration and later accretion. Study with high-dispersion spectroscopy the r- and s-process element distributions in the most metal-poor stars to probe early chemical enrichment of the halo. Extend these studies and the studies of Galactic

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.10 Low-resolution spectra obtained with the Keck telescope of z~4 galaxies of approximately L* luminosity. Positions of some of the prominent stellar and interstellar lines often found in the rest-frame far-UV spectra of star-forming galaxies are indicated. It is significant that despite the high rates of star formation, Lyman-alpha is seen in emission only about half of the time, as is the case here. Such spectra, which can now be obtained routinely (with a few hours’ worth of integration) on 8-m-class telescopes with high-efficiency, multiobject spectrographs, have revolutionized the study of the early universe. Courtesy of C.Steidel, California Institute of Technology.

globular clusters to local group members and, to the extent possible, to more distant local supercluster galaxies. Instrumentation required: wide-field multicolor imaging to identify candidates and, for follow-up, moderate- to high-resolution spectrographs.

  • Perform spectroscopic follow-up of samples of brown dwarfs in the Galaxy to study the frequency of binary systems and the evolution of their atmospheres; find evidence of chromospheres, flares, winds, and x-ray

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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coronas. Instrumentation required: moderate-resolution, low-back-ground, near-IR spectrographs.

  • Study the infalling envelopes, accretion disks, and post-accretion disks around young stars. Use adaptive optics and ground-based interferometry in the IR to measure the structure and temperature distribution in the 10- to 100-AU region, and use high-resolution spectroscopy to probe the 1- to 10-AU region via observations of velocity-resolved molecular transitions such as those of CO and H2O. Characterize the outflow regions of young stars and understand the transport of angular momentum and the evolution of magnetic fields. Look for structure in post-accretion disks indicative of planet formation and use coronagraphic imaging to search for high-mass planets and brown dwarf companions around neighboring stars. Instrumentation required: IR interferometers; AO-fed, near- to mid-IR, moderate-to-high-resolution spectrographs; coronographs.

  • Use adaptive optics imaging to monitor weather on Mars and the Jovian planets, climatic variations on Titan, and volcanic eruptions on Io and make the first high-resolution maps of surface features of Mercury. Adaptive optics with spectroscopy will provide spatially resolved spectra of the atmospheres of Jovian planets. Measure the binary frequency of KBOs and obtain spectra of brighter objects to study composition. Instrumentation required: optical-to-mid-IR AO imaging; AO-fed, moderate-resolution, near-to-mid-IR spectrographs.

  • Provide rapid-imaging follow-up of gamma-ray bursts to identify optical counterparts, and use sensitive spectroscopy to obtain host galaxy redshifts. Instrumentation required: instant-access O/IR cameras and low-resolution spectrographs.

  • Use AO and IR interferometry to map the structure of AGN at very small scales in order to study the kinematics, temperature, and density structure of material close to the black hole/accretion disk. Instrumentation required: AO-fed, O/IR spectrographs; IR interferometers.

GUIDELINES FOR THE TELESCOPE SYSTEM INSTRUMENTATION PROGRAM

Because public and private resources have a history of uncoordinated development, U.S. capabilities in ground-based O/IR astronomy represent a strong—but at best loosely organized—approach to astronomical research, with agendas set by a wide range of institutions pursuing a variety of goals. Although this diversity is one of the strengths

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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of U.S. astronomy, it is imperative that the new generation of 8-m telescopes be used as a total system in order for the nation to compete effectively. It has also become clear with the building of the 8-m telescopes that the resources necessary to instrument these telescopes properly, as well as to process, analyze, and distribute the data, are woefully inadequate. Traditionally, NSF grants have provided critical support for the processes of data gathering and reduction as well as for supporting theory and laboratory astrophysics programs essential for progress in O/IR research. However, the panel believes that NSF’s already important role can become even more important in the coming decade if it enables national and independent observatories to work together, as a single system, to accomplish the scientific goals described in this chapter. Through a process of peer review, NSF can use its grants programs to focus limited federal resources in a way that will maximize the scientific return on these huge investments by supporting the development of instrumentation that provides special, as yet unavailable observing opportunities.

A key component of the nation’s leadership has been the excellence of U.S. instrument builders, who have continually provided innovative, powerful, and cost-effective instrumentation for ground-based telescopes. Of particular concern is the training and support of future instrumentalists. The building of high-quality instrumentation, particularly in university environments, where students can be trained, is an essential component of a vigorous, diverse, ground-based telescope system. This instrumentation includes both traditional smaller (principal-investigator-scale) instruments as well as new, state-of-the-art facility instruments for 8-m-class telescopes. Compared with the former, the latter present special challenges: they are more expensive and more difficult to build, and they require larger groups, management structures, and longer production times. These challenges, as well as a disturbing lack of recognition in some university environments for this essential contribution to the scientific process, mean that many instrument builders see their opportunities for research hard pressed. Because instrument building at universities and observatories in the United States is crucial for the nation’s continued success in astronomy, the panel believes that it is vital for NSF to focus its efforts on ensuring a healthy mix of smaller-scale instrumentation programs and large-scale facility instruments.

The facilities instruments for the new generation of 8-m telescopes are far more capable than their predecessors, but because of their scale and complexity, they are an order of magnitude more expensive, typically

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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$5 million to $10 million apiece (the VLT average is $11 million). Furthermore, data storage, analysis, and dissemination costs will be substantial. Fortunately, the investment required is incremental to the funds already expended at both private and public observatories for construction and continued operation of the new telescope facilities. The panel proposes a new investment beginning at $5 million per year in instrumentation for the independent observatories, concentrated on the new 8-m-class telescopes, which would leverage a scientific yield several times over. Although the panel believes that the program originally proposed in the McCray report10 and recently reviewed and endorsed by the Committee on Astronomy and Astrophysics11 provides the framework for the administration of this program, here it emphasizes elements of the McCray report that have not been applied so far.

The McCray report recognized that maximizing the quality and quantity of astronomical research in the United States depends on a vigorous investment from NSF; the report also acknowledged NSF’s long-standing commitment to provide wide access to astronomical facilities, so that studies outlined in research proposals and rated as excellent through the peer review process could be carried out at premier facilities, public and private.

It is important to recognize that private facilities now support a large fraction of the U.S. astronomy community (~50 percent, according to the NRC report Federal Funding of Astronomical Research12), a situation very different from that existing when Kitt Peak National Observatory was founded in the 1950s. Although there are now many additional new opportunities for astronomical research, including space-based facilities, radio observatories, and data archives, it is abundantly clear that some measure of public access is vital to the health of U.S. astronomy.

The panel reaffirms the critical importance of maximizing scientific return and ensuring greater public access, and it emphasizes the crucial importance of regarding all of the U.S. O/IR facilities as a system. The

10  

Panel on Ground-Based Optical and Infrared Astronomy, National Research Council. 1995. A Strategy for Ground-Based Optical and Infrared Astronomy (Washington, D.C.: National Academy Press).

11  

Committee on Astronomy and Astrophysics, National Research Council. 1999. “On the National Science Foundation’s Facility Instrumentation Program” (Washington, D.C.: National Academy Press), June 2.

12  

Committee on Astronomy and Astrophysics, National Research Council. 2000. Federal Funding of Astronomical Research (Washington, D.C.: National Academy Press).

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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NSF should administer the TSIP so as to achieve all of these objectives. By employing an approach that recognizes the important contribution of nonfederal funds for astronomy, the NSF will encourage independent observatories to participate. To encourage their participation, the TSIP must be broader than the program first implemented, when the NSF’s goal of acquiring telescope time on private facilities dominated the process. Borrowing from the McCray report’s recommendations, the panel strongly advocates the following guidelines:

  • The TSIP should apply to facility instruments for independent observatories only, for which NSF grants at least $1 million in support of the proposed instrument. It would not replace existing Advanced Technologies and Instrumentation (ATI) or Major Research Instrumentation (MRI) programs.

  • Successful proposals that include an offer of observing time would provide nights on the telescope whose value (based on amortized investment and operations) amounts to 50 percent of the granted funds. This 50/50 split properly recognizes the initiative of the independent observatory researchers in bringing nonfederal funds to astronomical research and supports their science while still attending to the important goal of providing observing time for the best peer-reviewed proposals, regardless of institutional affiliation. (The panel also notes a finding from Federal Funding of Astronomical Research that 50 percent of the users of ground-based O/IR facilities have access to independent observatories.) The 50/50 split should not be negotiable: to negotiate it would undermine the cooperative spirit needed to ensure the success of the overall O/IR system. The proposing institution may specify additional guidelines, for example, whether the time is available only on the proposed instrumentation or on all instrumentation, and it may include requests that specify operating modes, for example, minimum observing run duration. Such conditions are to be evaluated along with other aspects of the proposal.

  • In lieu of some or all of the telescope time, proposals may be accepted that offer other comparable benefits to the astronomy community, for example, the production and dissemination of surveys and the archiving of data from this or other instruments on the telescope for which the instrument is proposed.

The panel considers the 50/50 split to be an essential part of its guidelines. It represents a fair division in which both communities

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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benefit. It is clear that a “dollar of telescope time for a dollar of instrumentation funding” does not recognize or encourage the contribution of universities and private institutions in raising funds and does not recompense them for the talent and time of their scientists and engineers in building facilities. On the other hand, an unrestricted NSF grant of funds with no benefit provided to the broader astronomy community would frustrate the aspirations of the scientists who would like to use the unique facilities outside the national observatories. Something for both groups is the only appropriate solution; the 50/50 split has the added benefit of conveying the traditional notion of fairness. Negotiating the split, as was tried previously, promotes competition that can only undermine the goal of cooperation within the system.

Effective development of the entire suite of community facilities as a system depends on a common perception of how the parts of that system interact; a common vision of the strengths, deficiencies, and potential evolution; and an implementation plan with some level of feedback and accountability. The panel looks to NOAO for leadership in involving all segments of the community in discussions aimed at evaluating elements of the system, establishing a common vision, and devising plans for the future. Based on the results of these discussions, NOAO should develop a strategic plan for the system that includes an analysis of the benefits, costs, and risks for various prioritized implementation alternatives. Such an analysis would help the NSF decide how to invest its resources, either proactively, through solicitations for particular capabilities or negotiations for telescope time, or through TSIP, in response to instrument proposals (see Figure 2.11).

Given the wide variety of instrument capabilities and performance, scientific potential, public benefit, terms of use of telescope time, and importance to the system of O/IR facilities, the choice of successful proposals should be conducted annually by an NSF-constituted peer review committee. Any recommendations from the NOAO-led strategic planning effort should be provided to that NSF committee, but the peer review process should allow a full consideration of all factors. Every year, the NOAO-led, community-based strategic planning group should provide structured feedback to the NSF regarding the perceived efficacy of its investments in meeting the strategic goals of the community.

The panel also considered the effectiveness of direct purchase of telescope time by the NSF and concluded that in some circumstances, this could be the most efficient way for the entire community to gain access to a unique capability. However, the panel prefers the TSIP

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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FIGURE 2.11 With the advent of diffraction-limited imaging on large ground-based telescopes, the center of the Galaxy has provided us with a unique testing ground for theories on galactic nuclei. On the left is an image of stars in the central 1 arcsec×1 arcsec (~0.035 pc) centered on the putative black hole, obtained with the Keck adaptive optics system in a short demonstration (exposure time=2 min). Speckle imaging at Keck over the last 4 years has been able to track the orbits of the brightest stars (right-hand panel), which reach velocities of up to 1400 km s−1 (0.5 percent of the speed of light). This is an example of how progress in instrumentation, adaptive optics in this case, can lead to breakthrough science. Courtesy of A.Ghez, University of California at Los Angeles.

approach because it—as opposed to the time purchase option—ensures the production of critically needed instrumentation and provides for community involvement (through peer review) in the types and capabilities of instruments that will be built and made available. For this reason, the panel recommends that the direct purchase of telescope time should be a second option, used sparingly so as not to significantly decrease the resources needed for TSIP, which would be sized according to the instrumentation needs of the independent observatories. It also urges that decisions by the NSF to buy telescope time should be guided by an understanding of the broad needs of the community, as is intended in TSIP.

The goal of building a more cohesive ground-based O/IR community—with increased incentives for private fund-raising, continued commitment to allowing public access to premier facilities, and maximized scientific creativity and output—should guide NSF policy through-

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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out the decade. Without these investments and increased funding for research support, both provided by the NSF grants program, U.S. astronomers will not be able to continue to play their leadership role in the most basic astronomical research and will not be able to take full advantage of the powerful new space telescopes such as Chandra, SIRTF, and NGST.

TECHNOLOGY ISSUES

The NSF could enhance the system of O/IR facilities through continued investment in the development of technologies that will ultimately enable new capabilities. Development of detectors, especially large-format, near- and mid-IR arrays, is a key area. AO systems to feed near-IR spectrographs are extremely important to reduce background and work in crowded regions of the sky. Large-scale surveys require new, more efficient data-handling techniques. IR interferometry will open a new discovery space for the study of high-surface-brightness objects and may spur the evolution of ground- and space-based filled-aperture telescopes.

COST ISSUES

The investment for the first complement of VLT instruments is $91 million, with an expected continuing investment of at least $10 million per year. These figures reflect a realistic assessment of the ongoing investment needed to take full advantage of the $500 million investment in new telescopes (excluding the investment for infrastructure at Paranal). With a comparable capital investment and an even greater number of telescopes, a continuing U.S. investment for major instrumentation of at least this magnitude is required. NSF has separate commitments for instrumentation at NOAO and Gemini, and some nonfederal support for instrumentation is available, leading the panel to conclude that an additional $5 million per year for the independent observatories is critically needed.

CONTEXT ISSUES

The importance of ground-based facilities for space-based telescopes and ground-based radio astronomy is clear. Most astronomical projects, regardless of wavelength domain, have an O/IR component that is

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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effectively addressed with ground-based O/IR facilities. The data collected should be archived and made available to the astronomy community, following the lead of the National Virtual Observatory (see the report of the Panel on Theory, Computation, and Data Exploration, Chapter 6). Support for instrumentalists is a particularly vital part of this program; the NSF can and should initiate programs that encourage and support instrument builders throughout the community. The greater participation of theoretical astrophysicists in the planning of large programs also needs encouragement and support.

OTHER ISSUES

The panel received valuable input from groups and individuals advocating programs and projects with particular scientific or technological thrusts. Described below are several that the panel found particularly meritorious:

  • Spurred both by revolutionary advances in large-area detectors and data-processing capability and by the scientific promise of a new generation of large telescopes that can enable the study of large samples, surveys play an increasingly important role in astronomical research. Although the panel’s main recommendations focus on the large individual effort to conduct a repetitive all-sky survey (LSST with WAVE), it is clear that the infrastructure needed for effective use of the vast amount of data collected in this and other surveys must be provided as well. Accordingly, the panel strongly endorses the National Virtual Observatory initiative, which would link many extant and future archives through common standards and protocols and would develop the tools to mine these archives effectively. The panel also calls attention to the substantial data sets from ground-based O/IR telescopes that are not integrated into archives. The development of archives for ground-based data represents a critical link between the independent observatories and the larger astronomy community. The NSF should explore (through NOAO) means for the systematic development of such archives.

  • A new and exciting class of problems could be tackled using highly multiplexed multi-object spectroscopy. While much thought and effort have gone into the development of arguments for imaging facilities having a large AΩ (aperture×field of view), it is also clear that the prospect of being able to work with samples of millions of spectra opens up the possibility of other studies, for example (1) tracing the evolution of

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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large-scale structure (for 1<z<4) and (2) understanding the dynamical history of our galaxy’s halo by locating and studying the remnant streams from individual merger or infall events. These questions should be pursued by initiating preliminary studies of this type and by understanding how best to develop such a capability, possibly through incorporation into the GSMT facility or later modification of the LSST facility.

  • It is clear that future very large facilities, whether they are in space or on the ground, will not be limited to filled apertures but, through interferometric imaging, will enable trade-offs in collecting area, dynamic range, and angular resolution. Although the panel endorses no specific interferometry facilities for the decade, there is a strong consensus to support development of interferometry techniques and facilities in order to understand those trade-offs.

  • Another important region of parameter space that deserves increased emphasis is the time domain. Diverse science returns, such as MACHO lensing discoveries and AGN reverberation mapping, would be enabled by facilities that provide synoptic capabilities complementary to the proposed LSST with WAVE survey initiative—for example, an array of medium-size telescopes distributed around the world or dedicated photometric/imaging monitoring telescopes. Many of these projects would benefit greatly from automated telescopes, which allow routine but complete observational programs to be carried out with minimal operating costs.

  • In addition to facilities that would target capabilities such as synoptic imaging, there is a need for supporting the specialized but limited projects that have been using the smaller national telescopes, for example, the spectroscopic monitoring of relatively bright stars for periodic and episodic activity, observations that are important for the theoretical modeling of stellar interiors and atmospheres. Recognizing that many important programs can be carried out with telescopes of modest aperture and that NOAO is likely to provide fewer such facilities in the future, the panel urges NSF to seek alternative means of supporting them—for example, by buying observing time at independent observatories or funding the development of specialized instrumentation.

  • The panel was excited by the prospect of new ground-based sites that offer unique windows through the atmosphere. One of these is the very cold site at the South Pole, the other is the very dry site in the Atacama desert of northern Chile. The South Pole site would support wide-field imaging with a 2-m telescope operating in the 2.4- to 5-µm

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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range, an important capability that would, for example, enable a census of brown dwarfs in the solar neighborhood.

  • Although the availability of CCDs and HgCdTe arrays continues to improve, there is a pressing need for better coordinated, aggressive development of larger format arrays, particularly IR array detectors. Collaboration between NSF and NASA to develop O/IR detectors could yield benefits for both ground- and space-based applications.

  • Laboratory astrophysics studies are crucial for many of the science domains discussed in this chapter. Particularly in studies of stars, where high-resolution spectroscopy enables the detection of thousands of unblended lines, it is essential to identify spectral lines of complex atoms, molecules, and their ions, together with oscillator strengths for these myriad transitions. Furthermore, quantitative models of stars are based on still-improving measurements of opacity, and nuclear physics provides the basis for understanding nucleosynthesis.

Of particular relevance for the science described here is the increasing importance of infrared observations, in the study of protostars or in the Galactic center, for example. As researchers probe the environments where stars and planets are born, an understanding of the complicated molecules and solid-state materials that dominate their observations depends on laboratory measurements. Also needed are good transition probabilities for the rare earth elements to probe the changing abundances of r-process and s-process elements, so important to the studies of chemical enrichment in the Galactic halo.

Although laboratory work of this nature is supported by a number of federal agencies, the relevant astrophysical work is dependent primarily on NASA and NSF funding. The panel urges both agencies to provide adequate support for the vital laboratory studies upon which so much astronomical work is based.

ACRONYMS AND ABBREVIATIONS

2MASS

—Two Micron All Sky Survey

AGB

—asymptotic giant branch

AGN

—active galactic nuclei

ALMA

—Atacama Large Millimeter Array

AO

—adaptive optics

ATI

—Advanced Technologies and Instrumentation (an NSF program)

AU

—astronomical unit (150 million km)

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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CARMA

—Combined Array for Research in Millimeter-wave Astronomy

CCD

—charge-coupled device

CELT

—California Extremely Large Telescope

Chandra

—Chandra X-ray Observatory (NASA, launched in 1999)

dof

—degrees of freedom

ELT

—Extremely Large Telescope

ESO

—European Southern Observatory

FOV

—field of view

FTE

—full-time equivalent

Gemini

—NOAO/multinational Northern and Southern Hemisphere 8-m telescope project

GSMT

—Giant Segmented Mirror Telescope

HII

—ionized hydrogen

HET

—Hobby-Eberly telescope

HST

—Hubble Space Telescope

IGM

—intergalactic medium

IMF

—initial mass function

IR

—infrared

ISM

—interstellar medium

KBOs

—Kuiper Belt objects

LSST

—Large-Aperture Synoptic Survey Telescope

MACHO

—massive compact halo objects

MAXAT

—Maximum Aperture Telescope

MRI

—Major Research Instrumentation (an NSF program)

MT

—million tons of TNT, a unit of energy

NASA

—National Aeronautics and Space Administration

Origins

—a NASA program

NEO

—near-Earth object

NGST

—Next Generation Space Telescope

NICMOS

—the near-infrared camera and multiobject spectrometer on the Hubble Space Telescope

NOAO

—National Optical Astronomy Observatories

NRC

—National Research Council

NSF

—National Science Foundation

NVO

—National Virtual Observatory

O/IR

—optical/infrared

QSO

—quasi-stellar object

OWL

—Overwhelmingly Large Telescope or Observatory at a World Level, an ESO proposal for a 100-m telescope

SDSS

—Sloan Digital Sky Survey

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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SIM

—Space Interferometry Mission

SIRTF

—Space Infrared Telescope Facility

SMA

—Submillimeter Array

TSIP

—Telescope System Implementation Program

VLT

—Very Large Telescope

VRI

—observations through visual, red, and infrared filters

WAVE

—Wide Area Variability Experiment

WIYN

—observatory run by the University of Wisconsin, Indiana University, Yale University, and NOAO

Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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Suggested Citation:"2 Report of the Panel on Optical and Infrared Astronomy from the Ground." National Research Council. 2001. Astronomy and Astrophysics in the New Millennium: Panel Reports. Washington, DC: The National Academies Press. doi: 10.17226/9840.
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In preparing the report,

Astronomy and Astrophysics in the New Millenium

, the AASC made use of a series of panel reports that address various aspects of ground- and space-based astronomy and astrophysics. These reports provide in-depth technical detail.

Astronomy and Astrophysics in the New Millenium: An Overview summarizes the science goals and recommended initiatives in a short, richly illustrated, non-technical booklet.

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