The Decade of Discovery in Astronomy and Astrophysics (1991) / Chapter Skim
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4. New Initiatives
4. New Initiatives
Pages 72-90
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From page 72... ...
Most of the instrumental initiatives result from advances in infrared technology, in spatial resolution, in the construction of large telescopes, and in the linking of electronic detectors to powerful computers. Four areas of research are currently of particular significance, and these will be used to illustrate the importance of the recommended instruments.
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From page 73... ...
What is the link between infrared-luminous galaxies and quasars? These questions will be explored using ground- and space-based telescopes with high spatial and spectral resolution operating at wavelengths from radio to gamma rays.
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74 Cal C)
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From page 75... ...
demonstrated that a telescope cooled with liquid helium could approach the theoretical sensitivity limit set by the faint light emitted by interplanetary dust grains. The 1,000-fold increase in sensitivity compared with that of earth-bound telescopes permitted IRAS to survey the entire sky at wavelengths from 12 to 100 ,um and to discover important new phenomena, including trails of solid material behind comets, disks of solid material orbiting nearby stars possibly the remnants of planet formation (Plates 2.1 and 4.1)
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From page 76... ...
Figure 4.1b shows SIRTF's expected sensitivity compared to the brightness expected for representative extragalactic objects. Figure 4.2 compares SIRTF with the European Infrared Space Observatory (ISO)
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From page 77... ...
= 100] compared with the predicted brightnesses of representative extragalactic objects scaled to a common redshift of 5, when the universe was only one-sixth its present size.
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From page 78... ...
In particular, spectral observations at these wavelengths hold the key to understanding the physics in regions of high density and moderate temperature that characterize the primitive nebulae around newly formed stars, and the cores of infrared-luminous galaxies and quasars. SOFIA's capability for diffraction-limited imaging and high-resolution spectroscopy at wavelengths inaccessible from the ground will complement SIRTF's great sensitivity at infrared and submillimeter wavelengths.
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From page 79... ...
For spectroscopy shortward of 5 Am, and at resolving powers in excess of 100,000 from 2 to 20 ,um, the infrared-optimized 8-m telescope will be more sensitive than a space-based one throughout the wavelength region accessible from the ground. The infrared-optimized 8-m telescope will make seminal contributions to problems requiring both high spatial and spectral resolution, such as probing the centers of dusty galaxies like our own to look for evidence of massive black holes.
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From page 80... ...
and include an Explorer mission to make a spectral survey of important classes of objects at submillimeter wavelengths; a ground-based survey of the entire sky at 1 to 2 sum with a threshold 50,000 times fainter than that of the only other survey, which is now 20 years old; allocation of funds to equip ground-based telescopes with revolutionary new infrared arrays; and a radio telescope using arrays of receivers to look for anisotropies in the cosmic background radiation that might provide clues to when and how galaxies formed. HIGH SPATIAL RESOLUTION Basic physical principles limit the smallest angle that a telescope can discern to a value approximately equal to the wavelength of the radiation observed divided by the characteristic size of the telescope.
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From page 81... ...
The MMA will provide observations in a wavelength regime and with spatial and spectral resolution that are highly complementary to the three infrared telescopes discussed above. The MMA will aid the studies of galaxy formation by detecting the
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This angle is only a few arcseconds at visible wavelengths. Partial corrections can still improve angular resolution and might utilize stars as faint as 15 magnitude separated by larger distances.
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In the past decade optical interferometers in the United States and Europe have produced useful scientific results, including wide-angle astrometry with thousandth-of-an-arcsecond precision, measurements of stellar diameters with a precision sufficient to constrain stellar atmosphere models, and the resolving of close binary stars. These projects have demonstrated that the key technologies are in hand to make interferometers using 1- to 2-m-diameter telescopes separated by baselines up to a kilometer, with corresponding resolution better than a thousandth of an arcsecond at a wavelength of 1 ,um.
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From page 84... ...
The facilities operated in the l990s would have a major impact on the study of individual stars, of newly forming stars, and of the compact cores of luminous galaxies that may harbor black holes. As discussed in Chapter 6, ground-based interferometers will provide tests of key technologies and concepts for future space interferometry and are an important part of a balanced program leading to major space facilities.
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From page 85... ...
AIM would demonstrate the technology required for future space interferometry missions. Large Earth-based Solar Telescope The Large Earth-based Solar Telescope is a solar telescope with a 2.4-m aperture that would use adaptive optics to increase the spatial resolution of solar observations.
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From page 86... ...
CONSTRUCTION OF LARGE TELESCOPES Optics technology has progressed to the point that telescope makers are confident of being able to build successfully the first optical and infrared telescopes larger than the 5-m Hale telescope. Recent advances in the technologies for casting and polishing of fast mirrors, in the precise alignment and support of segmented and monolithic mirrors, and in simple altitude-azimuth mounting will enable the construction of 8- and 10-m telescopes and will make the construction of 4-m-class telescopes less expensive.
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From page 87... ...
When completed in 1992, the Keck telescope will have 36 mirrors operating together as a single 10-m telescope. Courtesy of the California Association for Research in Astronomy.
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From page 88... ...
This pressure will increase as discoveries made with 8-m telescopes and the space observatories place insuperable demands on existing facilities for supporting observations. Examples of the range of important scientific programs requiring extensive time on 4-m-class telescopes include characterizing, through imaging and spectroscopy, the physical properties of sources discovered at nonvisible wavelengths; determining the interior structures of stars through long-term programs of spectroscopic monitoring of stellar oscillations; searching for planetary systems and subsolar mass objects by means of long-term radial velocity studies of large samples of stars; carrying out statistically complete spectroscopic and photometric studies of supernovae in galaxies and in active galactic nuclei; determining the mix of stellar populations in galaxies of a wide variety of ages and morphologies; mapping the large-scale structure of the universe out to a distance of 1 billion light-years (corresponding to redshifts of z ~ 0.1)
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From page 89... ...
mission to enter the Explorer queue for launch sometime around 1999. The committee strongly endorses the scientific importance of FUSE and recommends as its first choice in the moderate space category that this timetable for FUSE be ensured, and possibly accelerated, by the purchase of a dedicated spacecraft.
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From page 90... ...
The statistics of more than 2,000 events in a few years would lead to a better determination of the energy spectrum and the isotropy of these energetic cosmic rays. The improved spectrum would help detains whether the cutoff at energies of 102° eV, expected from pionproducing interactions of protons with the 2.7 K cosmic background radiation (the Greisen effect)
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