Working Papers Astronomy and Astrophysics Panel Reports (1991) / Chapter Skim
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Optical/IR from Ground
Optical/IR from Ground
Pages 47-74
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From page 47... ...
By using actively controlled optical elements to compensate for seeing, and by improving the figure on all mirror surfaces, it will be possible to concentrate the light from unresolved astronomical sources into a diffraction-limited core, and to provide significant gains in image quality for resolved sources. These new generation telescopes must be seen as the harbingers of optical/infrared facilities which by the latter half of the l990s promise to provide yet another order of magnitude increase in angular resolution.
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From page 48... ...
This unique facility must be built on the best site in the world - Mauna Kea, on the island of Hawaii. Its twin will provide the US astronomical community with the access to the southern celestial hemisphere essential in the era of the NASA Great Observatories, and can be optimized for performance at optical wavelengths.
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From page 49... ...
Dramatic advances in detector technology, telescope design, and computer controlled optical elements during the 1980s, provide the technical basis (see below) for constructing a new generation of large ground-based optical/infrared telescopes and auxiliary instruments capable of providing 10 times the angular resolution and up to 100 times the sensitivity of currently available ground-based telescopes.
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From page 50... ...
Appropriate samples of distant galaxies must be assembled from small area, deep imaging surveys with 4-meter class telescopes, and x-ray (ROSAT and AXAF) surveys for galaxy clusters.
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From page 51... ...
· through their ability to measure redshifts for these extraordinarily faint systems. Redshift determinations for systems at z > 3 at optical wavelengths require hours of time on current generation 4-m class telescopes, and are not yet possible in the near infrared even on the largest available telescopes.
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From page 52... ...
By use of adaptive optics, we can trace the distribution of solid material within the disk at effective spatial resolutions of ~ 5 to 10 AU, by observing light scattered by circumstellar dust. By virtue of their large collecting area, 8-m class telescopes will allow us to obtain disk rotation curves from analysis of R ~100,000 infrared spectra of photospheric light scattered by circumstellar dust, or of resonantly-scattered molecular line .
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From page 53... ...
With adaptive optics providing diffraction-limited images at 1.6 ~m, such objects can be imaged at separations as small as 10 AU from a companion PMS star in the nearest star-forming complexes. By locating substellar mass objects associated with PMS stars, we will 1)
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From page 54... ...
During the next decade, it will be necessary to build larger format optical and infrared detectors characterized by lower read noise, faster read times, and broader wavelength response. It is imperative that astronomy take full advantage of US strengths in advanced optical and infrared sensor technology to develop array detectors matched to the new generation of O/IR telescopes.
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From page 55... ...
The results of their efforts have borne fruit, and during the 1990s will enable: · sensitive imaging with diffraction-limited resolution (0.05" at 1.6 ,um and 0.02" at 0.55 ~m) using the full aperture of 8-m class telescopes by means of a technique known as adaptive optics; by comparison, HST will provide images of size ~ 0.07" at 0.55 ~m.
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From page 56... ...
more reference stars are available for effecting adaptive corrections for faint sources because no, To, and i are larger. Early applications of adaptive optics by European astronomers working with the 3.5m NTT in Chile have already produced images at 2.2 ,um in which a large fraction of the power is contained within a core whose size ~ that of the diffraction limit of the telescope.
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From page 57... ...
parallel advances in adaptive optics technology offer the promise of making use of the fall area of large array elements, and thus of building imaging systems capable of high sensitivity observations at infrared, and later, optical wavelengths. Interferometry, first with fixed baseline arrays of ~20-50m, and later with variable baselines extending to several hundred meters or longer, promises to provide infrared and optical images with angular resolutions exceeding 0.002".
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From page 58... ...
Neu' Science Enabled by D'ffra~ctio? ~-Limited Imaging The development of adaptive optics for use with 8-m optical/infrared telescopes will provide diffractionlimited images at near- and mid- infrared wavelengths, ~ ~ 1.6 ,um by mid-decade, thereby improving image quality by nearly tenfold when compared with typical atmospheric seeing.
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From page 59... ...
; The gains offered by adaptive optics are potentially so great that we recommend that during the decade, all 8-m telescopes in the US be equipped with systems capable of full adaptive corrections ire the near-~nfrared. Full corrections at optical wavelengths will involve more complex wavefront sensors and adaptive mirrors, and will likely be achieved only toward the end of the decade, following investment in a significant research and development program.
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From page 60... ...
will thus be spectacular. Recommended Program for the 1 990s The scientific programs enabled by 8-m class telescopes equipped with adaptive optics make it certain that such facilities will be among the leading tools of research and discovery during the next decade.
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From page 61... ...
for developing and building advanced auxiliary instruments required both for the new generation of large O/IR telescopes. Instruments for these new generation telescopes will be large in scale, technically sophisticated, and in many cases far more expensive than analogous auxiliary devices on extant 4-m class telescopes.
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From page 62... ...
distortions in the incoming wavefront by use of wavefront sensors and adaptive mirrors; use of adaptive optics at the ESO NTT has produced near-infrared (2.2 ,um) images in which a significant fraction of the light is concentrated in a diffraction-limited core of diameter ~0.14".
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From page 63... ...
of efforts to extend the wavelength range for full adaptive corrections from the near-infrared to optical wavelengths. This funding level assumes the prior commitment of $10M$15M to build adaptive optics systems for full wavefront correction in the near infrared-already included as an integral part of our recommended program to construct and instrument the new generation of large O/IR telescopes.
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From page 64... ...
Without adaptive optics, the largest telescope apertures that can be used effectively in interferometric arrays are comparable to the coherence length (rO) for an incoming wavefront: lm to 2 m at near-infrared wavelengths, but only 0.1 m to 0.2 m at optical wavelengths (see Table 1~.
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From page 65... ...
University involvement in operation and management of these facilities will have the added benefit of providing opportunities for deep student involvement in both carrying out long term and/or exploratory programs and in developing novel instrumentation. Our recommended program to construct four new generation 4-m class telescopes during the next decade is the minimum required to meet the most pressing needs of the community.
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From page 66... ...
These surveys promise to provide fundamental databases for cataloging the distribution and brightnesses of galactic and extragalactic objects - the ultimate basis for designing a wide range of scientific programs for ground-based and space-based telescopes. The O/IR panel recommends the completion of digital all sky surveys at (1J near-infrared, and (2J optical wavelengths before the end of the decade.
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From page 67... ...
The panel wishes to note that the recommended infrared and optical all sky surveys are deemed the most pressing and important representatives of a much larger class of more specialized surveys (e.g. narrow-band imaging surveys at Ha and H2 enabled by modern optical and infrared detector technology)
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From page 68... ...
At optical wavelengths, CCDs provide an order of magnitude improvement in sensitivity for most applications over the previous generation of detectors, and provide major improvements as well in geometric and photometric stability. With current noise levels approaching a few electrons rms, and quantum efficiencies near 80 percent, they are very nearly ideal detectors.
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From page 69... ...
It is important to emphasize that the total $10M is not to be spent at $1M/year; it is critical that the first installment of $5M be provided immediately so that the large format chips be purchased and available for timely installation on the new generation Am and 8-m telescopes. Infrared Arrays: The Future for the 1-5 ,um Region" The NICMOS (Near Infrared Camera, Multi-Object Spectrograph)
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From page 70... ...
A new generation of large telescopes is planned which, if built, will quadruple presently available light gathering power. Adaptive Optics hold the promise of diffraction-limited imaging by these telescopes, and offer more than an order of magnitude gain in angular resolution.
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From page 71... ...
New techniques for polishing large 8-m primaries for the telescopes of the 1990s appear extendable to these requirements. Fundamental to the utility of large single apertures is the development of adaptive optics: the advantage of diffraction-limited imaging increases very rapidly with aperture.
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From page 72... ...
potential for scientific return; (2) evidence of strong student involvement in the design, construction and use of the instrument; (3)
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From page 73... ...
OPTICAL/IR FROM GROUND III-27 construction and use. Second, it would result in the revitalization of a variety of local facilities, providing opportunities for student and faculty research on programs requiring imagination and a willingness to trade time for aperture.
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From page 74... ...
VVOODGATE, NASA Goddard Space Flight Center
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