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Report of the Panel on Solar Astronomy



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Astronomy and Astrophysics in the New Millennium: Panel Reports 5 Report of the Panel on Solar Astronomy

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Astronomy and Astrophysics in the New Millennium: Panel Reports SUMMARY The study of the Sun has revealed fundamental physical puzzles that have resisted understanding for generations of astronomers. The Sun is a typical star, with other stars being at least as complex. Solving mysteries on the Sun—among others, the dynamo process, the intermittency in the surface magnetoconvection, and the heating of the active corona—is important for all of astronomy and astrophysics. The Sun offers unique opportunities for physical insight that go far beyond just resolving astrophysical processes on their intrinsic scales. These opportunities include (1) using the Sun as a plasma physics laboratory, (2) understanding and predicting the impacts of the Sun on Earth’s climate and on “space weather” in the near-Earth environment, and (3) understanding the role of solar evolution in the evolution of life in planetary systems. The successes achieved in solar research since the 1991 survey report1 lead us to expect that many of these mysteries can be resolved by the new projects prioritized in this report. However, it should be kept in mind that at this time, key solar mechanisms are poorly understood even as they are applied in other astrophysical contexts. Or, fascinating new phenomena might be discovered that will give rise to new puzzles to challenge new generations of physicists. STRATEGY FOR THE DECADE 2001 TO 2010 The progress of the past decade was made possible by investments made in the 1980s that led to revolutionary observational capabilities in space and on the ground, including simultaneous multiwavelength observations of dynamics, precision vector magnetic field measurements, and helioseismology. Breakthroughs in numerical simulations of two-and three-dimensional magnetohydrodynamical (MHD) processes allowed for tailoring solarlike scenarios on the computer. All these advances have led to the formulation of a new strategy—a systems approach—for solar physics in the next decade: 1   Astronomy and Astrophysics Survey Committee, National Research Council. 1991. The Decade of Discovery in Astronomy and Astrophysics (Washington, D.C.: National Academy Press).

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Astronomy and Astrophysics in the New Millennium: Panel Reports The domains of the solar interior, photosphere, chromosphere, corona, and heliosphere should be treated as a single system. Diverse data sets should be integrated, as demonstrated in the NASA Solar Data Analysis Center (SDAC). The connection to the operational branches of space weather research should be exploited much as weather research received from the National Weather Service is exploited. International efforts should be integrated as much as possible. OBSERVATIONAL EFFORTS CURRENT Observational facilities in operation. The Dunn solar telescope with the Advanced Stokes Polarimeter and its adaptive optics (AO) program, the McMath-Pierce telescope with its infrared program, and the Fourier-transform spectrograph should be operated until the Advanced Solar Telescope (AST) becomes available. The seismology network GONG and the Mauna Loa Solar Observatory should be continued. The various university observatories should be maintained at a level that will ensure a broad educational base. The space-based observatories—Yohkoh, SOHO, Ulysses, and TRACE—should be maintained and given adequate funding for data analysis. Observational facilities under construction. SOLIS (on the ground) and HESSI, Solar-B, STEREO, and Solar Probe (in space) are of utmost importance for expanding some findings of the last decade in critical areas. FUTURE Primary recommendation, ground-based, medium size: the Advanced Solar Telescope (AST). In view of solar physics’ growing relevance to the climate research and space weather communities, AST should be built and become operational within this decade. Key astrophysical processes will be directly observable with the AST and AO. Half of the $64 million investment would come from international partners.2 Secondary recommendation, ground-based, medium size: the 2   The estimated costs for ground-based initiatives include costs for instrumentation, grants, and operations, as described in the preface.

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Astronomy and Astrophysics in the New Millennium: Panel Reports Frequency-Agile Solar Radiotelescope (FASR). This state-of-the-art radio observatory would be primarily for solar observations that can be readily scheduled in coordinated campaigns. Cost: $15 million. Primary recommendation, ground-based, small size: the expansion of SOLIS to a three-station network around the globe. This would give nearly continuous coverage in full-disk solar vector magnetic field monitoring and would form the backbone of an assessment of the solar magnetic flux budget over the solar cycle. Cost: $4.8 million. Primary recommendation, space-based, medium size: Solar Dynamics Observatory (SDO). SDO would pursue in particular the newly discovered tomography of subsurface structures through time-distance analysis of running waves at the solar surface and impulsive helioseismology from oscillations of loops in the corona. Cost: $300 million. THEORY AND DATA MINING The panel recommends a broadened Solar Magnetism Initiative (SMI) as a comprehensive research framework for theory and data mining for all of the above projects. Understanding in solar physics can be advanced through detailed multidimensional numerical modeling. SMI will provide the coordination between observational activities and numerical experiments in forward modeling, to be done by modelers in solar physics as well as plasma physics and turbulence theory. SMI will be a community-wide research program that has been broadened from its original scope to become a multiagency enterprise. The cost of the program is estimated to be $3 million per year for 5 years, with the option of extension for another 5 years. Since SMI is proposed as a multiagency enterprise, it is not ranked with respect to ground-based or space-based projects but stands on its own. NEW TECHNOLOGIES An adaptive optics system for a 4-m-class AST needs to be pursued based on recent dramatic progress in the existing project at the National Solar Observatory (NSO) and international cooperation. The development of lightweight mirrors (like Solar-Lite) to achieve high resolution in the medium and far IR will break the cost curve for future space missions. The development of Stokes polarimeters in the UV will allow for measurements of the magnetic field in the chromosphere.

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Astronomy and Astrophysics in the New Millennium: Panel Reports POLICY ISSUES NSO should be enabled to take its lead role in developing the AST through changes in its managerial structure. Broad community participation needs to be ensured. The allocation3 between the National Science Foundation’s (NSF’s) university grants program (about 63 percent) and its funding to centers in the U.S. solar and solar terrestrial community (37 percent) is appropriate and healthy. Increases in overall funding are necessary, however, given the increased need to understand the Sun for space weather forecasting and for the driving of climate. Additional educational outreach activities will also be required. WHY DO SOLAR PHYSICS RESEARCH? The complexities of the Sun—its internal structure, rotation, and convection and the resulting cyclic and random generation of its magnetic fields and the magnetoactive, hot, explosive, extended solar atmosphere and solar wind—are fascinating and challenging (see Figure 5.1). Because these solar phenomena occur over physical scales that cannot be simulated in laboratories on Earth, their study tests and expands our understanding of magnetofluid dynamics and plasma physics. Solar physics is key to much of astrophysics and central to the Sun-Earth connection, and it bears on the quest to determine the origin and extent of life in the universe. KEY TO THE MAGNETODYNAMIC UNIVERSE Dynamic magnetic fields are widespread throughout the universe; they are an active ingredient of many astronomical objects, from dwarf stars to accretion disks to clusters of galaxies. Our understanding of the origins and effects of these distant astrophysical magnetic fields is rudimentary at best. The Sun has the most intense magnetic field in the solar system. The entire corona and solar wind and diverse explosive events (many producing bursts of high-energy particles, x rays, and gamma rays 3   From the Task Group on Ground-based Solar Research, National Research Council. 1998. Ground-based Solar Research: An Assessment and Strategy for the Future (Washington, D.C.: National Academy Press). Also known as the Parker report for committee chair Eugene Parker.

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Astronomy and Astrophysics in the New Millennium: Panel Reports FIGURE 5.1 Superposed images of aspects of solar variability. Top left: composite of an event with a modest flare, the brightest eruptive prominence seen so far by SOHO/EIT, and a 400 km/s CME seen by SOHO/LASCO. Top right: the Sun from RISE/PSPT in CaK. Bottom from left to right: plot of solar luminosity and the sunspot cycle; auroral curtain during a magnetic storm; H.Averkamp painting of skaters during the Little Ice Age, when solar activity was low during the 17th century (Hendrik Averkamp, Winter Scene on a Canal, c. 1615, oil on panel, 18 7/8×37 5/8 in., Toledo Museum of Art, Toledo, Ohio; purchased with funds from the Libbey Endowment, Gift of Edward Drummond Libbey, acc.no. 1951.402). Top left images courtesy of the SOHO/EIT and SOHO/LASCO consortia. SOHO is a project of international cooperation between ESA and NASA. Top right image courtesy of Radiative Inputs of the Sun to Earth/Precision Solar Photometric Telescope Project.

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Astronomy and Astrophysics in the New Millennium: Panel Reports and other large events blasting magnetized matter out past the planets) are all magnetodynamic effects. The Sun is a unique laboratory that will lead to an understanding of the dynamic behavior of cosmic magnetic fields. SOLAR-TERRESTRIAL PHYSICS Life on Earth depends on the Sun’s heat and light. Earth’s climate, the state and extent of the upper atmosphere and magnetosphere, and space weather inside and outside the magnetosphere are determined and driven by the Sun’s luminosity, by its UV and x-ray spectrum, by the solar wind, and by explosive events on the Sun. Solar irradiance variations appear to be correlated with the level of the Sun’s magnetic activity. Extrapolated luminosity changes due to changes in the Sun’s production of magnetic field over decades and centuries are large enough (>0.1 percent) to significantly affect Earth’s temperature, contributing to global warming and “little ice ages.” Changes in the Sun’s magnetic activity change the output of UV and x rays by factors as large as 10 or more. These radiations control Earth’s thermosphere, ionosphere, and protective ozone layer. Coronal mass ejections (CMEs) on the Sun blast out massive magnetic clouds that plow through the solar wind and impact Earth, causing magnetic storms that can disrupt power systems. In near-Earth space and throughout the solar system, high-energy particles from these events often reach levels that can be lethal to spacecraft and astronauts. To better understand and predict global change and space weather, we need to understand and predict the mechanisms and behavior of their driver, the magnetic Sun.

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Astronomy and Astrophysics in the New Millennium: Panel Reports ORIGIN AND EVOLUTION OF LIFE ON PLANETS Acting over the age of the solar system, the solar wind may well have played a major role in the evolution of planetary atmospheres. It has been suggested that Mars currently has little atmosphere because it has long had, as now, little magnetic field, allowing its early atmosphere to be blown away by the solar wind. To evaluate the magnitude of such effects, astronomers need to understand the Sun’s production of magnetic field, the mechanisms underlying the acceleration of the solar wind, and their variation over solar cycles and longer times. Similar considerations apply to the Sun’s output of UV and x rays over its history—with this output being controlled by the solar magnetic cycle. Some stars with activity cycles exhibit much greater variability than the present Sun, suggesting that the Sun might have had very active phases in the past. An understanding of the magnetic Sun will form a basis for estimating how stellar magnetism could influence the possibility of life arising on other planets throughout the universe. THE MOST SIGNIFICANT ADVANCES IN THE LAST DECADE GOALS ACHIEVED Many of the goals for solar physics laid out in the 1991 survey report have been met or surpassed, as can be seen below. THE SOLAR INTERIOR Thin flux-tube calculations have been successful in reproducing the synoptic properties of flux emergence over the solar cycle, thereby placing stringent bounds on the magnetic field strength at the base of the convection zone (several 104 gauss). The radiative core of the Sun rotates as a solid body, while the observed surface differential rotation persists to the base of the convection zone. A thin boundary layer, the tachocline (thickness less than 0.05 solar radii), exists at the radiative core convection zone interface and is a propitious site for the solar dynamo. The rotation amplitude between 0.68 solar radii (just below the convection zone) and 0.72 solar radii (just above it) varies locally up to 25 percent over a period of 1.3 years.

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Astronomy and Astrophysics in the New Millennium: Panel Reports Solar model structures validated by helioseismology rule out an astrophysical solution to the solar neutrino problem and underscore the necessity of elemental diffusion and settling in the Sun’s radiative core. Local helioseismology (Hankel decomposition, time-distance analysis, and acoustic holography) images to a depth of ~20,000 km subsurface signatures of extant and emerging active regions and has detected steady poleward, near-surface meridional flows of 10 to 30 m/s. THE SOLAR SURFACE Magnetic fields emerge in strong-field concentrations with significant electric currents and helicity. Through convective collapse and the buoyancy of the magnetized plasma, the fields rapidly orient themselves perpendicularly to the solar surface and are enhanced to superequi-partition levels of approximately 1500 G. The rate of appearance (and disappearance) of the surface magnetic flux, particularly in the form of small-spatial-scale ephemeral regions, is such that the average observed unsigned flux in the quiet Sun would be doubled in approximately 40 h. The fact that the average unsigned flux varies by a factor of only 3 to 5 over the entire solar cycle implies that these emerging fluxes must be rapidly “recycled” under the action of a local surface magnetic dynamo. Model calculations indicate these local dynamo processes provide sufficient magnetic energy for the heating of the outer solar atmosphere. A significant fraction of a sunspot’s magnetic flux is contained in the penumbra, which has a deep fluted structure. Radial spokes of nearly horizontal magnetic field alternate with spokes in which the field is inclined some 40 deg. Evidence indicates that the emergence of active regions leads to excess facular emission that exceeds the deficit of the sunspot umbrae and penumbrae. Numerical simulations are beginning to address the question of how deep in the convection zone these irradiance variations first arise. The total change in solar irradiance over a solar cycle, however, remains unexplained. THE OUTER SOLAR ATMOSPHERE AND HELIOSPHERE Both theory and observation now show that the chromosphere and the transition region cannot be regarded as nested physical atmospheric layers with a distinct identity. Rather, their characteristic spectral

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Astronomy and Astrophysics in the New Millennium: Panel Reports signatures arise from radiatively weighted averages of nonlinear magnetohydrodynamic processes that are highly variable in both space and time and that force the tenuous plasma to be far from radiative equilibrium. There is a nascent appreciation that the signatures of wave propagation, magnetic reconnection, and nanoflares are imprinted on the line profiles of UV and EUV emission features, allowing the relative contribution of these processes to the heating of the solar atmosphere to be determined from data with sufficient resolution in wavelength, space, and time. The reconnection of post-CME loops has been detected through their continuous glow in soft x-ray emission. The synthesis of radio, x-ray, and white-light coronal images has begun to reveal the intricate manner in which the corona ejects magnetized material (carrying magnetic helicity) in the guise of CMEs while liberating magnetic free energy through flares (magnetic reconnection events) possessing a continuous spectrum of sizes. The diffuse x-ray irradiance of the corona shows a pronounced variation with the solar cycle. This variation exceeds the variation expected from the number and size of active regions. The first-ionization-potential (FIP) effect is absent in high-speed solar wind streams, implying that the structure and dynamics of the upper chromosphere are fundamentally different in coronal hole regions and the rest of the Sun. Heating in the coronal acceleration region of the high-speed solar wind leads to large ion-temperature anisotropies and very large perpendicular ion temperatures, implying that ion cyclotron heating is a major source of the energy required to drive these streams. THE SOLAR-STELLAR CONNECTION This report cannot be a comprehensive review of all of stellar physics. Hence, the panel concentrates on two examples where the synergy between solar and stellar work is particularly beneficial and includes the sharing of instrumentation. During the last decade, studies of stellar magnetic activity have made significant progress in some respects, but in others they have been handicapped by the lack of adequate tools for some of the observations. Ground-based spectrographic and photometric studies of bright-field stars, including the Mt. Wilson HK (hydrogen and calcium line) photometry program, the High Altitude Observatory

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Astronomy and Astrophysics in the New Millennium: Panel Reports (HAO)/Lowell Solar-Stellar Spectrophotometer, and the Tennessee State University network of photometric telescopes, have delineated the broad features of stellar magnetic activity. The broad dependencies of stellar activity on stellar temperature and rotation rate are starting to be understood, as are the connections between these properties, a star’s age, and the photospheric abundances of lithium and beryllium. The Sun displays an unusually small ratio of photometric to chromospheric variability; this fact is central to the understanding of sunspot and facular contributions to time variations in the solar flux, but it also has the consequence that accurate solar analogues are difficult to find. In order to gain samples of stars that are larger, more homogeneous, and better defined with respect to their mass, age, and composition, access to larger telescopes to observe fainter stars is required. Astroseismology of Sun-like stars would make critical contributions to solar-stellar problems, better defining the fundamental parameters of the stars under study and helping to reveal their internal processes. So far there are no methods to reliably measure the tiny oscillating signals produced by stars similar to the Sun. Progress has been made in radial velocity observations of a few of the brighter stars. Further efforts in calibration methods, combined with suitable high-resolution echelle spectrographs, can be expected to bring a hundred or so nearby solar-type stars within the reach of this technique. A more far-reaching avenue for the application of seismic methods is photometry from space. Unhindered by atmospheric absorption and scintillation, a modest-size telescope would be able to analyze stellar pulsations in many Sun-like stars in the nearer open clusters. The first steps toward such precise photometry missions are now being taken, involving observations of a few bright-field stars; recent results have come from the star tracker on the WIRE spacecraft, while small photometry missions have been selected for flight by France, Canada, and Denmark. A SYSTEMS APPROACH TO SOLAR PHYSICS—TOWARD A DECADE OF UNDERSTANDING The scope of solar research and the methods for performing it are expanding in several respects: (1) the Sun is being treated as one physical system, (2) solar research is being systematized, (3) diverse datasets are being integrated into a framework, (4) connections are being forged

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Astronomy and Astrophysics in the New Millennium: Panel Reports SOLAR TERRESTRIAL PROBE MISSIONS Particle Acceleration Solar Orbiter (PASO) PASO will address the fundamental question of how the Sun accelerates particles to high energies in solar flares and CMEs. It is designed to use solar sailing to achieve a near-synchronous orbit at 0.16 to 0.2 AU, that is, an orbital period about equal to the solar rotation period. This would allow continuous observation of particle acceleration from active regions and CME-related solar features from their birth through their rise to a maximum and decay. PASO would provide hard x-ray/gamma-ray imaging of flares with 25 to 36 times the sensitivity and 5 or 6 times the linear spatial resolution of observations from 1 AU. Neutrons of energies below tens of MeV and down to ~1 MeV, which can provide direct evidence for acceleration of low-energy ions, would only be detectable by getting this close, since they decay in flight (e-folding decay time of ~1000 s). Getting this close is also the only way to obtain measurements of the energetic particles freshly accelerated by CME shocks before they have been significantly modified by scattering and energy changes. Finally, PASO will provide the first systematic exploration of the inner (<0.16 to 0.3 AU) heliosphere. Reconnection and Microscale Probe (RAM) The RAM is designed to investigate the structure and dynamics of the magnetized coronal plasma with continuous broadband solar observations from the L1 orbit. It aims to understand the microscale instabilities that lead to reconnection and, ultimately, to flares and CMEs. The probe will be equipped with an ultrahigh-resolution telescope imaging the Sun at 195 Å with a resolution of 0.02 arcsec. It will perform high-resolution spectroscopy (0.2 arcsec from 0.3 to 10 keV) and high-resolution EUV spectroscopy at 170 to 220 Å. The probe is projected to be a Solar-Terrestrial Probe (STP) mission. It is a follow-up mission on TRACE, SOHO-EIT, and Yohkoh, going for the specific problem of reconnection. It will have to be equipped with large-format cryogenic imaging detectors, which are under development. THEORY AND DATA MINING: THE SOLAR MAGNETISM INITIATIVE The SMI concept of a comprehensive research program involving

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Astronomy and Astrophysics in the New Millennium: Panel Reports the various facilities and the solar community was introduced earlier. SMI would include a series of focus programs on particular aspects of the problem; these would be carried out by groups of scientists collaborating in extended workshops at a single location supported by appropriate computing, observing, and data analysis resources. Candidate topics include the solar dynamo and interior dynamics; magnetic flux transport through the convection zone; an observational description of emerging magnetic flux; the history of magnetic flux; the solar magnetic cycle at the solar surface; and the physics of coronal mass ejections, their causes, and heliospheric effects. It is expected that each focus program would take about 1 year, with intensive workshops every 6 months at which progress would be compared and coordinated. At the end of each focus program, results would be presented to the broader community in a workshop or at a scientific meeting. The SMI would be overseen by a steering committee that could be modeled after the CEDAR steering committee. In addition to defining the focus programs described above, it would advise on scientific priorities throughout the life of the program, coordinate observing campaigns, and keep the community informed and involved though newsletters and presentations at scientific meetings and workshops. Two- and three-dimensional simulations of MHD processes mimicking some of the processes on the Sun have been undertaken with great success by many groups in the United States and elsewhere. There are major numerical efforts at the following universities: University of Colorado at Boulder, Harvard University, Michigan State University, Stanford University (Lockheed), University of California at Berkeley, University of Alabama at Huntsville, University of Chicago, University of Rochester, and Yale University, as well as at the Bartol Institute, NASA Goddard Space Flight Center, National Center for Atmospheric Research/High Altitude Observatory, Naval Research Laboratory, and the San Diego Supercomputer Center/Science Applications International Corporation. To take advantage of the rapidly increasing quantities of solar observational data (from, for example, the SOLIS instruments) and to expand the effort in numerical modeling, SMI will need about $2 million per year in funding for an expanded university grants program. Grants would be awarded following standard NSF procedures for directed programs, such as CEDAR and GEM. To entrain new scientists with recent Ph.D.s into SMI, a program of at least two SMI postdoctoral fellowships should be established, to be

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Astronomy and Astrophysics in the New Millennium: Panel Reports TABLE 5.5 Estimated Annual Investments for the Solar Magnetism Initiative Initiative Annual Investment ($) University grants program and SMI postdocs 2,200,000 Focus programs, workshops, and coordination 90,000 Centralized scientific support and community service 500,000 hosted by any institution involved in SMI. The appointees would be chosen in a community-wide competition according to a process to be determined by NSF. Some centralized support would also be needed to develop the community Stokes inversion program, which is essential for utilizing the new and greatly expanded vector magnetograph data expected from SOLIS, and to support observing campaigns, focused programs, and the SMI database, which provides both observational and modeling data (Table 5.5). There would also be some one-time costs for hardware for the SMI database, proposed to reside at the National Center for Atmospheric Research (NCAR)/HAO. It is expected that supercomputing requirements for SMI, particularly for numerical modeling and Stokes inversions of data, while not small, can be accommodated within current plans to upgrade the NCAR Scientific Computing Division’s supercomputing capability and by some of the NASA centers. TECHNOLOGIES FOR THE FUTURE ADAPTIVE OPTICS The AST project will develop a visible adaptive optics (AO) system. A multiconjugate adaptive optics (MCAO) system based on this technology will achieve diffraction-limited resolution over fields of view (FOVs)

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Astronomy and Astrophysics in the New Millennium: Panel Reports significantly larger than the isoplanatic patch size of, typically, a few arcseconds. The Sun is an ideal object for the development and application of MCAO since the multiple wavefront measurements as a function of the FOV required for MCAO can be performed using solar structure as the wavefront sensing target. The complexity involved in having to use multiple laser guide stars can be avoided. MCAO should therefore be developed for the Sun first. The AO development is proposed as a collaborative effort of NSO and NJIT/Big Bear Solar Observatory, the Center for Adaptive Optics, and international partners. SOLAR-LITE Solar-B will have 150-km resolution, 10-G sensitivity to the line-of-sight field component and 100-G sensitivity to the transverse component. Solar Probe will provide the first glimpse of the line-of-sight magnetic field with 10-G sensitivity at 50- to 25-km resolution. Solar-B will have the resolution to isolate separate elementary flux tubes (150 km in diameter); Solar Probe will have the resolution to look within a tube but will not measure the transverse component. Measurement of the transverse component is essential for determining the three-dimensional configuration of the field. Now is the time to begin defining and developing the science and technology for the next-generation, high-resolution solar mission. The development of a lightweight mirror larger than the 50-cm mirror of Solar-B, as begun in the Solar-Lite technology studies, will lead to less expensive instruments than those envisioned for OSL/SOT, which was planned for in the 1991 survey report but never built, for financial reasons. HIGH-RESOLUTION VECTOR MAGNETOMETRY OF UV LINES Measurements are needed of the three-dimensional vector of the magnetic field in lines formed above the photosphere, in the field-dominated, force-free domain of the solar atmosphere. This requirement is motivating the development of new filters and polarimeters for vector magnetography of UV lines formed in the chromosphere and low transition region.

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Astronomy and Astrophysics in the New Millennium: Panel Reports CONNECTION TO LABORATORY ASTROPHYSICS ATOMIC/MOLECULAR/NUCLEAR PHYSICS Identification of EUV line spectra. Of more than 800 observed lines, SOHO has revealed that 300 or so between 500 and 1600 Å are unidentified. Accurate laboratory wavelengths. Laboratory measurements for Mg X and Ne VII lines found in the corona/transition region are of insufficient accuracy or missing altogether. The NIST spectrograph should follow up with measurements accurate to 1 part in 200,000. Photoionization resonances. The OPACITY project data for He I show resonances close to the Fe IX/X and Fe XII lines emitting in the TRACE bandpasses, with energies uncertain to 1 eV. High-resolution measurements of the photoionization resonance structure of neutral or singly (doubly) charged ions of abundant elements are needed. Collision cross-sections for particle impact. A new area of research recently opened up using the Hanle effect in Stokes spectra obtained inside the solar limb. Many details of the atomic physics involved in the collisional depolarization need to be measured to much greater accuracy than can presently be achieved in the laboratory. Landé g factors. The Landé g factors of absorption lines of complex atoms (e.g., Fe I and Fe II) depend on the configuration mixing. As the infrared becomes accessible to high-resolution Stokes measurements, precise g factors for Fe I and Si I are needed. Neutrinos. The LOWL instrument provided proof that the neutrino deficit as it is measured for the solar neutrino flux on Earth is not due to a deviation of the solar structure from the standard model. The key lies in the regime of particle physics. A continuation of measurements of neutrinos is, however, essential to determine finite mass and possible magnetic moment of the neutrinos. PLASMA PHYSICS Basic plasma physics and magnetohydrodynamic processes, which are thought to be central to solar physics, can be studied in the laboratory. The Magnetic Reconnection Experiment (MRX) device at Princeton has been used for a series of magnetic reconnection experiments. One of the main issues studied by MRX is the relationship between the

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Astronomy and Astrophysics in the New Millennium: Panel Reports reconnection region, which is extremely small, and the global magnetohydrodynamic equilibrium. The results have been successfully interpreted as magnetic reconnection at the Sweet-Parker rate. The basic device is a modified plasma fusion reactor design of a type known as Spheromak. There have been other contributions from laboratory plasma physics in the areas of anomalous thermal conductivity and anomalous resistivity, relaxation of plasma to a force-free state, and dynamo activity. Such experiments have an important role in solar physics, providing a basis for theory and interpretation of observation. POLICY AND EDUCATIONAL ASPECTS The panel examined issues surrounding the standing of solar physics in the U.S. university community and the overall balance between the NSF grants program and the two NSF solar physics centers—NSO and HAO. It also considered how a major development project like the AST should be optimally organized within the United States as well as with international partners. THE UNIVERSITY-BASED SOLAR PHYSICS COMMUNITY IN THE UNITED STATES Driven by the successes of solar space missions and by helioseismology, there has been a rejuvenation of solar physics at U.S. universities, with two new departments having been established. There is a vigorous university research community in solar physics built mostly on research faculty positions rather than on regular faculty. However, several traditional chairs for solar physics at some major universities were not refilled as they became vacant. This development continues to be of concern in view of the growing importance to society of understanding the Sun in the context of space weather and climate change. It also contrasts starkly with the scientific opportunities and the apparent strong interest of the many excellent young researchers who work in the field supported by soft money. The reasons for this development lie partly in the shift in emphasis from solar (and stellar) physics in astronomy to solar physics in the geophysical context. Neither the funding agencies nor the universities have yet been able to address the challenge posed by the changing astrogeophysical framework for solar physics. The panel urges them to do so.

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Astronomy and Astrophysics in the New Millennium: Panel Reports FUNDING ASPECTS Appendix G of the Parker committee report documents the balance of funding between NSF grants to universities and funds spent on NSF-supported centers (NSO and HAO). In solar physics research, about 63 percent of NSF funding goes to grants and 37 percent to centers. This is very similar to the balance between NCAR (the largest NSF center) and grants in atmospheric science. The panel regards the balance of funds in solar support by NSF as healthy. The overall demographics in the solar community should be adequate to support and fully exploit the missions and programs planned for the next decade, except that more faculty positions are needed. If NASA provides funding for strong guest investigator programs and NSF provides funds sufficient to run and exploit new ground-based observing capabilities, there will be new incentives for universities to hire faculty. THE NATIONAL SOLAR OBSERVATORY The panel endorses the recommendation of the Astronomy and Astrophysics Survey Committee’s Panel on Education and Public Policy that the NSO should be separated from the nighttime parts of the National Optical Astronomy Observatories as soon as is reasonable. This would allow the best possible posture for NSO and the solar community to advocate and develop the AST, which should be (and is becoming) the primary future focus for NSO. NSO should then establish structures that ensure broad community participation in preparing and building the AST. The panel also recommends that postfocus instrumentation for the AST be developed in collaboration with the community, with instrument packages outsourced but developed under overall guidance from a central authority for AST. In addition, the panel sees many advantages to having international partners in the AST project, provided adequate control remains with the United States. EDUCATION For the broader educational outreach aspects the panel refers the reader to Chapters 4 and 5 of the survey committee report. Solar physics can contribute considerably to the educational effort in astronomy. In particular, the highly dynamical nature of solar processes—like CMEs, which can be observed with high time and spatial resolution—make solar

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Astronomy and Astrophysics in the New Millennium: Panel Reports observations an attractive means of portraying astrophysical concepts to the public. There is a need to educate the growing community of space weather forecasters in solar physics as well as decision makers in government and in industry. ACRONYMS AND ABBREVIATIONS 1HT —One Hectare Telescope ACOS —Advanced Coronal Observing System AIA —Atmospheric Imaging Assembly AO —adaptive optics ASP —Advanced Stokes Polarimeter AST —Advanced Solar Telescope AU —astronomical unit CCD —charge-coupled device CDR —concept and design review CEDAR —Couplings, Energetics and Dynamics of Atmospheric Region, a part of the NSF solar influences program CIA —Coronal Imaging Assembly (on SDO) CME —coronal mass ejection EIT —Extreme Imaging Telescope (part of SOHO) ESA —European Space Agency EUV —extreme ultraviolet FASR —Frequency-Agile Solar Radiotelescope FIP —first-ionization potential FOV —field of view FPIP —focal-plane instrumentation packages GEM —Geospace Environment Modeling, a part of the NSF solar influences program GOES —Geostationary Operational Environmental Satellite, a series of meteorology satellites GONG —Global Oscillations Network Group HAO —High Altitude Observatory HESSI —High Energy Solar Spectroscopic Imager HMI —Helioseismic and Magnetogram Imager (on SDO) IF —intermediate frequency produced when a radio receiver mixes the input signal with a local oscillator IR —infrared ISAS —Institute of Space and Astronautical Sciences (Japan)

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Astronomy and Astrophysics in the New Millennium: Panel Reports ISOON —Improved Solar Observing Optical Network KPVT —Kitt Peak Vacuum Telescope LASCO —Large Angle and Spectrometric Coronagraph Experiment LOFAR —Low-Frequency Array LOWL/ECHO —Low-degree/Experiment for Coordinated Helioseismic Observations MCAO —multiconjugate adaptive optics MDI —Michelson Doppler Imager, an instrument on SOHO MHD —magnetohydrodynamics MPT —McMath-Pierce Telescope (on Kitt Peak) MRX —Magnetic Reconnection Experiment (at Princeton University) NASA —National Aeronautics and Space Administration NCAR —National Center for Atmospheric Research NJIT —New Jersey Institute of Technology NOAA —National Oceanic and Atmospheric Administration NRL —Naval Research Laboratory NSF —National Science Foundation NSO —National Solar Observatory OPACITY —A solar physics project conducted by the Institute of Physics, Bristol OSL —Orbiting Solar Laboratory (never-built NASA project) OVRO —Owens Valley Radio Observatory PASO —Particle Acceleration Solar Orbiter PSPT —Precision Solar Photometric Telescope RAM —Reconnection and Microscale Probe RISE (SunRISE) —Radiative Inputs of the Sun to Earth, a part of NSF solar influences program SAIC —Science Applications International Corporation SDAC —Solar Data Analysis Center SDO —Solar Dynamics Observer SETI —search for extraterrestrial intelligence SMEX —Small Explorer (NASA) SMI —Solar Magnetism Initiative SOHO —Solar and Heliospheric Observatory Solar-B —NASA mission to measure magnetic field and luminosity of the Sun SOLIS —Synoptic Optical Long-term Investigation of the Sun SOON —Solar Observing Optical Network SOT —Solar Orbiting Telescope (never-built NASA project) SRBL —Solar Radio Burst Locator

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Astronomy and Astrophysics in the New Millennium: Panel Reports STEREO —Solar-Terrestrial Relations Observatory STP —Solar-Terrestrial Probe THEMIS —Heliographic Telescope for the Study of Magnetism and Instabilities on the Sun (French/Italian project) TRACE —Transition Region and Coronal Explorer UV —ultraviolet WIRE —Wide Field Infrared Explorer

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