Working Papers Astronomy and Astrophysics Panel Reports (1991) / Chapter Skim
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Interferometry
Interferometry
Pages 107-128
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From page 107... ...
These new instruments will undertake systematic imaging in the infrared and visible of stellar surfaces and circumstellar material and of bright galactic nuclei, and will search for gravitational radiation from neutron stars and other condensed objects. In the first decade of the next century, we foresee construction of great interferometric observatories on the earth and in space, performing astrometric measurements to microarcsecond precision and obtaining imagery of the faintest sources with angular resolution substantially better than 1 milliarcsecond.
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From page 108... ...
We therefore recommend, for the latter part of the decade, the development of a plan for a Very Large Optical Array, to be built in the period 2000-2005. Composed of perhaps 20 medium-aperture telescopes, each equipped with adaptive optics, this array will achieve aperture synthesis imaging with sub-msec resolution of active galactic nuclei, novae, stellar accretion disks and QSO's.
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From page 109... ...
In the earliest phase, a small number of operational telescopes could be activated, perhaps optimized for a high priority capability such as high dynamic range imaging or sub-psec astrometry, with such science goals as detection and study of planets in other systems, or measurement of the accretion disks in active galactic nuclei. In subsequent years, additional telescopes could be added to reach the final configuration, offering imaging of the faintest sources.
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From page 110... ...
A wide range of astrophysical information, accessible in no other way, may be revealed from gravitational wave observations, such as the evolution of asymmetries in the core of a supernova, and the rate at which condensed stars fall into supermassive black holes out to z=3. The technology is now at hand to achieve the direct detection of gravitational waves, to measure the waveforms and determine the direction, frequency, and polarization, and to deduce the size and shape of the sources.
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From page 111... ...
. Recommended Programs for the 1990's Ground-Based Interferometry Large Optical/Infrared Interferometry with Multiple Telescopes MediumrAdapt Eve Optics Development alla Implementation Small Planning for Very Large Optical/Infrared Array Space Interferometry Large Interferometric Astrometric Mission Medium Technology Development: Advanced Space Interferometer Small | Techn Logy Development: Gravitational Wave Observatory in Space $50M $35M $3M $200M $20M $20M Infrared and Optical Interferometry No astronomer needs to be convinced of the fantastic capability of a space-based optical and IR interferometer operating with km-length baselines and with sufficient sensitivity to produce maps of faint sources down to 0.1 msec resolution.
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From page 112... ...
Fortunately, simpler facilities recommended for this decade will make critical contributions toward many science goals, especially the astrophysics of young and evolved stars, bright galactic nuclei, novae, and the narrow emission-line regions of active galactic nuclei. To be useful as an imager, a high resolution instrument must also have adequate sensitivity and dynamic range.
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From page 113... ...
Proper motions of the Large and Small Magellanic Clouds would make possible independent determinations of the total mass of the Galaxy and thus would tell us the amount of "dark matter" it contains. Because of their brightness, we have an almost complete sample of the galactic globular clusters.
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From page 114... ...
To summarize, the further development of IR/visible/UV interferometry should be undertaken with the goals of precision astrometry and high angular resolution imaging. Such capabilities will revolutionize many areas of astrophysics by providing the first morphological information on structurally complex systems.
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From page 115... ...
The importance of such an instrument has been recognized previously by the scientific community in various NASA and National Academy reports (Space Science Board, 1981; Physics Survey Committee, 1986; Space Astronomy MOWG, 1981~. Although much valuable work could be done with a narrow-angle instrument, there is a considerable advantage to an interferometer that can directly measure large target separations.
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From page 116... ...
AGN's and the cores of "normal" galaxies are especially amenable to study with this technique. For instance, measurements of velocity dispersion near the center of normal galaxies such as M31 or M32 indicate that they may contain 107 Me black holes.
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From page 117... ...
Although there are strong theoretical grounds for their existence in large numbers, no confirmed detection has been yet made. Since the dwarf is close to the brighter primary, high angular resolution and dynamic range are required.
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From page 118... ...
However, with an artificial reference source to ensure a plane wavefront across the telescope aperture, a much fainter celestial reference may be used, and only low order information is required of it. A Program for Development and Implementation of Adaptive Optics A large and continuing DOD investment goes into adaptive optics.
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From page 119... ...
Valuable limits on the intensity of gravitational waves reaching the Earth have been set by a combination of terrestrial antennas of different kinds, including Doppler tracking of distant spacecraft and timing measurements on millisecond pulsars. We will describe here two proposed gravitational wave observatories using laser interferometers as broadband antennas, and the opportunities for obtaining entirely new types of astrophysical information with them.
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From page 120... ...
Rotating Neutron Stars. Advanced detectors in the LIGO could detect the gravitational waves from a neutron star anywhere in our galaxy if its equatorial ellipticity exceeds Emin ~ 10-9 ~ Prowl msec)
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From page 121... ...
Probably the most interesting burst source for LAGOS is inspiral signals from white dwarfs, neutron stars or ~ 10Me black holes orbiting around central supermassive black holes (SMBH's) in AGN's or quasars.
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From page 122... ...
The corrected laser wavelength is then used to determine changes in the difference in arm lengths due to gravitational waves and instrumental noise. The effect of the residual laser wavelength variations is reduced because they are nearly common mode for the two arms.
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From page 123... ...
INTERFEROMETRY lo~6 10-4 1o~2 1 102 104 10- 14 t HI 1, _ ~ ~ GP5 Oopp,er { m~ lo~16 t ~ '''''W ,~.
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From page 124... ...
It is only for isotropic extragalactic background that the limitation of having a single antenna is likely to be substantial. Until the LAGOS antenna is developed, the principal technique for searching for low frequency gravitational waves will continue to be Doppler tracking of distant spacecraft using microwave transponders.
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From page 125... ...
The primary requirements on the system are that it keep the spacecraft centered on the test mass, and that it maintain the spacecraft orientation accurately with respect to the laser beam transmitted by one of the other spacecraft. A Disturbance Reduction System is needed to protect the test mass inside each spacecraft from spurious accelerations which could mask the effects of gravitational waves.
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From page 126... ...
Space Astronomy MOWG, 1981, Space Astronomy Program Plan for the 1980's and 1990's, NASA. Space Science Board, 1981, Strategy for Space Research in Gravitational Physics in the 1980's, National Academy Press.
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From page 127... ...
reprinted from Koechlin, L., 1984, in Kilometric Optical Arrays in Space, ESA SP-226, ed.
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From page 128... ...
CLARK, Massachusetts Institute of Technology CARL E FICHTEL, NASA Goddard Space Flight Center HERBERT FRIEDMAN, Naval Research Laboratory RICCARDO GIACCONI, Space Telescope Science Institute JONATHAN E
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