Astronomy and Astrophysics in the New Millennium Panel Reports (2001) / Chapter Skim
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7 Report of the Panel on Ultraviolet, Optical, and Infrared Astronomy from Space
7 Report of the Panel on Ultraviolet, Optical, and Infrared Astronomy from Space
Pages 327-374
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From page 327... ...
- 7 Report of the Panel on U~tra\1~o~et, Optca~, and Jntrare] Astronomy from Space
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From page 328... ...
MANOR M BSSIONS When it prioritized major missions, the panel assumed that the Space Interferometry Mission (SIM) , one of the initiatives recommended in the 1991 survey committee report, will be flown and that the Hubble Space Telescope (MST)
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From page 329... ...
The far infrared presently has enormous discovery potential. The single most important requirement is improved angular resolution.
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From page 330... ...
Other core science includes studies of protostellar disks in Orion-like environments and starburst galaxies at z < 1. An 8-m-class W/optical telescope will achieve gains of 100 to 1000 over the current capabilities of the Hubble Space Telescope, especially when combined with the next generation of energy-sensitive detectors for the W/optical bands.
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From page 331... ...
Energy-resolving detectors, both superconducting tunnel junctions (STJ) and transition-edge sensors (TES)
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From page 332... ...
WOIR astronomy flourished in the decade 1990 to 1999. The Hubble Space Telescope was launched, repaired, and enhanced to produce images of unparalleled resolution and depth and spectra that are only now being rivaled by the new class of giant telescopes on the ground.
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Hipparcos, the European astrometric survey satellite flown early in the decade, provided the most accurate map of stellar positions in history. The European Infrared Space Observatory (ISO)
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From page 334... ...
Even from space, the optics of a telescope create insurmountable limits to the observation of a faint planet next to a bright star unless the telescope is enormous 100 m in diameter, say or the starlight is reduced by interference effects. The study of planet building through observations of the circumstellar disks from which planets are born is easier but nevertheless demands much higher angular resolution at infrared wavelengths than anyone has attempted.
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From page 335... ...
The Hubble Space Telescope sees deeply into the universe but not yet deeply enough to see the "edge of light," where the first stars and galaxies came into existence after the Big Bang. Both HST and FUSE are still inadequate to detect faint quasars needed to map out the intergalactic medium using observations of their absorption lines.
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From page 336... ...
In fact, modest investments in technology are likely to increase astronomical capability in several areas where alternative approaches are very expensive, so these relatively inexpensive recommendations are among the most important. A55UMED FACILITIES THE RUBBLE SPACE TELESCOPE The panel fully supports the recommendations relating to the Hubble Space Telescope contained in the 1996 report of the Dressler committee, HST and B |
From page 337... ...
It will be the only facility covering the ultraviolet portion of the spectrum, and its imaging power at all wavelengths will remain a necessary adjunct to the suite of facilities planned for the coming decade. THE SPACE INTERFEROMETRY MISSION The 1991 survey committee report, The Decade of Discovery in Astronomy and Astrophysics,4 recommended an astrometric interferometry mission as a high priority.
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From page 338... ...
Distances to a selected sample of stars throughout the Galaxy will refine our understanding of galactic structure, and in particular the structure of the Galactic halo, thus tracing the distribution of dark matter. Searching for planets near stars in the solar neighborhood is the most ambitious of SIM's goals.
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From page 339... ...
· Exploit the enormous discovery potential associated with improving sensitivities in the infrared by several orders of magnitude and image sharpness by a factor of 10. NGST will reveal the nature of the universe at high redshifts using a combination of multicolor deep surveys and spectroscopy of a representative sample of galaxies.
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SIRTF will achieve 300 My Angular resolution (2-,um, diffraction limited)
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From page 341... ...
The open circles were measured by ground-based observatories, and the filled circles are measurements with the Hubble Space Telescope. The box in the lower left-hand corner shows that the most distant supernovae that can be observed with HST are atz = 1.2.
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Of particular importance will be NGST's ability to FIGURE 7.2 A portion ofthe Hubble Deep Field. The eight blue circles identify the galaxies whose near-infrared spectra can be observed with an 8-m-class ground-based telescope; the red circles markthe sourcesforwhich only NGSTwill be ableto study the spectraatwavelengths longerthan about 2.5 ,um, allowing physical analysis ofthese faint galaxies.
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From page 343... ...
The orange dashes show the sensitivity limits of the Hubble Deep Field in its six wavelength bands. The solid yellow curve shows the sensitivity of an NGST Deep Field after an exposure time of I million seconds about I O days.
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From page 344... ...
The diffuse infrared background radiation reaching us from the cosmos is an indicator of the total energy generated by stars and active galactic nuclei since the end of the dark age. Most of this background radiation probably originates in dusty young galaxies and their nuclei, where energy generated by stars and accretion onto massive black holes at optical and x-ray wavelengths is absorbed by dust and reradiated in the infrared.
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Given the large factors by which NGST improves upon the sensitivity and angular resolution of its precursors, it has an enormous discovery potential. It typically improves observational capability over all precursor missions by a factor of 1000.
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The deployable sunshade and the deployable primary mirror enable missions at both far-infrared and W wavelengths. Cryocooler development is of interest to the same two categories of .
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CO) Temporalresolution <1 s Fringe sensing FOV 0.25" 3,um 1.0" 12,um Lifetime >5 years Cost category Major NASA funded · Survey of ~150 stars to determine the frequency of planetary systems with planets the size of Earth or larger; · Low-resolution spectroscopic observations of ~50 planetary systems, looking for broad, strong spectral lines such as CO2 and H2O; · High-resolution spectroscopy of about five planetary systems to search for O3 or CH4; and · Milliarcsecond images of ~1000 astronomical objects at infrared wavelengths providing unprecedented views of protoplanetary disks, galactic nuclei, starburst galaxies, and galaxies at high redshift, as well as many other interesting objects.
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It will have a spatial resolution of 0.1 AU at the distance of the nearest star formation regions and 0.4 pc at a distance of 100 Mpc for extragalactic
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· Observations of the hot dust surrounding a giant black hole in a galaxy nucleus. TPF will provide a direct test of unification theories for active galactic nuclei.
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. vloratlon Passive cooling Infrared detectors Interferometric system .
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Total M o D E RATE M ~ s s ~ o N S $ 415 million 180 million 110 million 125 million 1300 million 200 million 200 million $2115 million S jNG~E-APERTURE FAR-I INFRARED OBSERVATORY The parameters for SAFIR, a passively cooled, 8-m-class, far-infrared telescope in a distant orbit (probably L2) it could be an NGST clone with a modified sunshield are given in Table 7.4.
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From page 353... ...
FIRST = 2400 My at 90,um 100 My (300,um) FIRST = 3500 My at 180,um Angular resolution 0.8" (30,um)
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From page 354... ...
In some galaxies and in many regions within our galaxy, the dust is so dense that the far-infrared light dominates the energy output. Equally important, the dust is almost transparent in the far-infrared spectrum, making it possible to penetrate dusty clouds and galaxies with infrared observations and see the objects producing the original radiation: stars and accretion onto giant black holes.
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From page 355... ...
The vast majority of the bolometric luminosity from regions of star formation at redshifts below 2 is in the far infrared. Furthermore, SAFIR provides continuous coverage of the spectrum, especially important to observe spectral features such as the mid-infrared lines that distinguish active galactic nuclei (AGN)
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From page 356... ...
This far-infrared background is thought to arise from starburst galaxies at redshifts between 1 and 3, meaning that roughly half the young galaxies radiate primarily in the far infrared. If so, it will be necessary to resolve this background into its components and measure the farinfrared luminosities of the individual sources to understand the history of heavy-element synthesis after the Big Bang.
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From page 357... ...
Cooling by pure molecular hydrogen is believed to play a major role in the earliest phases of galaxy formation in the early universe, before heavier elements like oxygen and carbon had been formed. To observe the formation of these primordial galaxies at high redshifts, far-infrared telescopes with large apertures are essential.
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From page 358... ...
dominant phases of dust-embedded star formation and nuclear activity throughout the universe (Figure 7.81. The Hubble Deep Field revealed many galaxies too faint to contribute significantly to the far-infrared background.
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From page 359... ...
As for the speed of an observation the astronomical capability defined in the 1991 survey committee report, an 8-m far-infrared telescope will be 105 times faster than SIRTF and more than 103 times faster than FIRST at the longest wavelengths where they overlap. This enormous discovery potential is what most impressed the panel when it was making its recommendation for this .
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From page 360... ...
This $2.5 million might be included in the cost of the mission. Cost The panel requested a detailed cost estimate from scientists at the Goddard Space Flight Center and the Space Telescope Science Institute based on NGST costs.
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The cost estimate below, which has been adjusted to FY2000 dollars, assumes reduced mission operations costs and a 5-year lifetime. Although this telescope is recommended as a moderate-class mission, its cost is very close to the boundary that separates moderate from major missions, and the panel recognizes that it could just as appropriately be classified as a major mission, as was done in the survey committee report.
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From page 362... ...
~ 35m i/~\ ~ 3 x 104, S/N = 10 in 4 x 104 s NGST will give ~0.06" at 1 ,um Very high resolution is a stretch goal MCP and STJ responsesa NGST spin-off assumed aMCP is microchannel plate and STJ is superconducting tunnel junction. the universe dominated by unseen (dark)
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From page 363... ...
Although some weak tensing studies can be done from the ground, experience with the Hubble Space Telescope has shown that the amount of dark matter on large scales is most accurately determined in space. The availability of a very small, stable point-spread function and the access to the blue-light characteristic of the background galaxies at z < 1 gives SWO wide-field imaging a significant advantage.
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SUVO could map this intergalactic structure that may contain most of the normal matter in the universe through systematic observations of many quasars. Courtesy of R.-Y.
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From page 365... ...
This feedback of radiation and energy modulates the rate at which galaxies continue to accrete gas and determines how heavy elements are spread throughout the universe. Studying Galactic Star Formation With Hubble, spectral imaging in the optical and ultraviolet proved its value in measuring the products of star formation in local regions of the Milky Way.
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From page 366... ...
SWO will allow astronomers to map out the large-scale distribution of dark matter and the nearly invisible warm components of the cosmic web of gaseous matter that may dominate the missing baryons. Technology Development No high-throughput W/optical mission will be possible without significant NASA investments in technology, including W detectors, gratings, mirrors, spectrographs, and imagers.
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From page 367... ...
Examples of the kind of science that can be carried out with balloons include searches for planets with a coronagraph on a diffraction-limited telescope a few meters in diameter; the imaging of convective flows and magnetic fields in the Sun's photosphere with a large solar telescope; extragalactic observations with a moderate-size far infrared telescope; and all-sky surveys at hard x-ray wavelengths. The top of the stratosphere is far superior to terrestrial sites and enables a wide range of 367
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From page 368... ...
Resonance transitions from small particles are commonly observed that lack counterparts in the limited number of laboratory studies of solid-state lines. It is already the case that space missions reveal spectral lines that are unidentified owing to a lack of laboratory data.
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TECHNOLOGY FOR THE FUTURE ENERGY-SENSITIVE WV/OPTICAL DETECTORS A revolution is occurring in the technology for ultraviolet detectors. Two technologies, superconducting tunnel junctions (STJ)
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From page 370... ...
Far-infrared detectors typically must be cooled to a few kelvin. Far-infrared telescopes require optics below about 10 K to achieve their full potential.
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However, investment in new ground stations permitting vastly increased telemetry bandwidths is likely to be needed if we are to realize the enormous gains made possible by the advanced detector arrays that will be used with the next generation of space science missions.
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Although how much money would be needed to achieve this breakthrough technology is unknown at present, the panel believes it would be prudent to invest several million dollars per year to explore the means of manufacturing very large, accurate optical surfaces for future space telescopes. ACRONYMS AND ABBREVIATIONS AGN active galactic nuclei ALMA Atacama Large Millimeter Array AU astronomical unit, a basic unit of distance equal to the separation between Earth and the Sun, about 150 million km
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. Imaging MO S multiobj e ct spectrograph NASA National Aeronautics and Space Administration NGST Next Generation Space Telescope, an 8-m infrared space telescope 373
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From page 374... ...
a mission to produce high-resolution pictures of one quarter of the sky and to measure the redshift of distant galaxies SMEX Small Explorer, a NASA program to fly small, inexpensive satellites on a rapid timescale ST-3 NASA's Space Technology 3, two spacecraft launched together and put into an orbit around the Sun to demonstrate interferometry STJ superconducting tunnel junctions SWO Space Ultraviolet Observatory, a proposed 8-m-class telescope SWAS Submillimeter Wave Satellite, one of NASA's Small Explorer missions; it studies interstellar clouds TDRSS Telemetry Data Relay Satellite System TES transition-edge sensors TPF Terrestrial Planet Finder, a free-flying infrared interferometer designed to study terrestrial planets around nearby stars ULDB ultralong-duration balloon flights W ultraviolet WOIR ultraviolet, optical, and infrared VLT Very Large Telescope, the European Southern Observatory's four 8-m telescopes
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