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NASA NTRS1986

Far-infrared observations of Sagittarius B2 - Reconsideration of source structure

New moderate-angular-resolution far-infrared observations of the Sagittarius B2 star-forming region are presented, discussed, and compared with recent radio molecular and continuum observations of this source. In contrast to previous analyses, its far-infrared spectrum is interpreted as the result of a massive frigid cloud overlying a more-or-less normal infrared source, a natural explanation for the object's previously-noted peculiarities. The characteristics derived for the obscuring cloud are similar to those found for the W51 MAIN object. Both sources have high sub-millimeter surface brightness, a high ratio of sub-millimeter to far-infrared flux, and numerous regions of molecular maser emission.

Thronson, H. A., Jr.↗
NASA NTRS1985

A wide latitude CO survey of molecular clouds in the III galactic quadrant

Molecular clouds in the third galactic quadrant from 180-280 galactic longitude were surveyed in the 115.271 GHz line of CO at an angular resolution of 0.5 deg. In galactic latitude the survey covers from b = -5 to +5 deg, with a few extensions to higher latitudes. A preliminary analysis of the data allowed the determination of distances and masses of at least 30 molecular clouds related to the Perseus arm and to the Cygnus, or outer, arm. The studied clouds are located between 2.5 kpc and 10.7 kpc from the sun with most of the masses between 30,000-700,000 solar masses, and only three up to two million solar masses. The most interesting result comes from the distribution of the clouds distance from the galactic plane that indicates a warp in the arms to which these clouds belong.

May, J.↗
NASA NTRS1985

Elimination of directional wave spectrum contamination from noise in elevation measurements

The Surface Contour Radar (SCR) is a 36-GHz computer-controlled airborne radar which generates a false-color-coded elevation map of the sea surface below the aircraft in real time, and can routinely produce ocean directional wave spectra with post-flight data processing which have much higher angular resolution than pitch-and-roll buoys. The SCR range measurements are not error-free and the resulting errors in the elevations corrupt the directional wave spectrum. This paper presents a technique for eliminating that contamination.

Walsh, E. J.↗
NASA NTRS1986

Speckle interferometry applied to asteroids and other solar system objects

Speckle interferometry is a high angular resolution technique that allows study of resolved asteroids. By following the changing size, shape, and orientation of minor planets, and with a few general assumptions (e.g., geometric scattering, triaxial ellipsoid figures, no albedo features), it is possible to directly measure an asteroid's true dimensions and the direction of its spin axis in one or two nights. A particular subset of triaxial ellipsoid figures are equilibrium shapes, and would imply that some asteroids are thoroughly fractured. Such shapes if they exist among the asteroids would allow a determination of bulk density since there is a unique relation among spin period, size, shape, and density. The discovery of even a single rubble pile, (just as the finding of even one binary asteroid by speckle interferometric techniques) would drastically alter the notion of asteroids as small solid planets. The Pluto/Charon system was studied to aid in improving the orbital elements necessary to predict the eclipse/occultation season currently in progress. Four asteroids were reduced to their size, shape, and pole direction: 433 Eros, 532 Herculina, 511 Davida, and 2 Pallas.

Drummond, J. D.↗
NASA NTRS1986

International Halley Watch: Discipline specialists for radio science

Some 34 radio observatories in 18 countries are participating in the Radio Science Net of the International Halley Watch. Approximately 100 radio astronomers are contributing to this effort, which has included observations of comets P/Crommelin and P/Giacobini-Zinner as well as P/Halley. It is clear that the record of data for the 18 cm OH ground state lambda doublet, which provides fundamental information on the gas production rate, kinematics, and potentially the magnetic field in the coma, will be vastly more complete and of higher accuracy than has even been obtained on any previous comet. The coverage by a number of radio observatories will enable short period variations to be studied and correlated with simultaneous data obtained at other wavelengths. Likewise, the first definitive detection of the important parent molecule hydrogen cyanide in a comet was obtained and is being studied by groups in the United States, Sweden, and France. The first detection of the comet with the Very Large Array telescope operated by NRAO was achieved and has produced exciting results for the distribution of emission at high angular resolution from the OH radical. At this writing data are still being obtained and being processed, and there are still strong indications that exciting information will be obtained from radar studies of P/Halley and from searches for additional parent molecules.

Irvine, W. M.↗
NASA NTRS1986

The molecular gas in the supernova remnant IC443

Although a few highly perturbed regions characterized by gas motions with velocities larger than 20 km/s have been discovered during the last several years in the supernova remnant (SNR) IC 443, the nature of these perturbed clumps and their relationship to the quiescent molecular gas near the SNR remains unknown. In part, this is due to a lack of large-scale, high angular resolution observations. Therefore, a systematic survey of this SNR in the CO (J=1 yields 0) line has been conducted, covering a roughly 50' x 50' region spaced by 2'. The observations were made with the 14 m telescope of the Five College Radio Astronomy Observatory (FCRAO), which has a resolution of 45" and a single sideband receiver temperature of 200 K at 2.6 mm wavelength. Five new clumps were discovered, bringing the total number of known perturbed regions to eight. To study the physical structure of these clumps in more detail, more complete maps of the clumps have been made in both the CO(J=1 yields 0) and (J=2 yields 1) transitions with the FCRAO telescope. These maps show that the extent of perturbed gas in a typical clump is several arcmin, or a few pc at a distance of 1.5 kpc.

Huang, Y. L.↗
NASA NTRS1987

The gamma-ray spectrometer experiment on the solar maximum mission satellite

The major activities summarized include: Gamma-Ray Spectrometer (GRS) instrument response and flight operation; solar flare studies; cosmic gamma-ray studies; summary of computer operations; search for flare-precursor protons; diffuse galactic annihilation radiation; cosmic ray bursts; atmospheric gamma ray spectrum; gamma ray line emission from supernovae and novae; improved angular resolutions using Earth occultation; and production processing of NASA IPD data. In addition, an updated list of published papers and invited papers or contributed papers presented at scientific meetings is provided.

Chupp, E. L.↗
NASA NTRS1987

Discrete X-ray sources and the X-ray background

Since the discovery of a highly uniform X-ray background (XRB) in the 2 to 10 keV range, its nature is not yet fully explained. It appears clear from the results of Einstein medium and deep surveys that at least 50% of the XRB is due to individual extragalactic sources when their contribution is integrated to Z = 3. This includes contribution from Quasi Stellar Objects (QSOs), Active Galactic Nuclei (AGNs), galaxies, and clusters of galaxies. The average spectrum of each of the individual contributing sources is softer than that of the observed XRB. Therefore, the remaining contribution must have a rather hard spectrum of alpha nearly equal to 0.0 to 0.2. It is unlikely that this spectrum can be produced by diffuse processes. Therefore, the remainder of the XRB must be due to individual sources with the appropriate spectrum. This requires either that the spectrum of the already identified sources changes at early epochs or a new class of objects. Advanced X-ray Astrophysics Facility (AXAF) observations will extend survey sensitivity to limiting fluxes of order of 3 x 10 to the minus 16 erg/sq cm/s, some 50 times fainter than any previous survey. There will be sufficient sensitivity and angular resolution to permit identification and study of these objects.

Giacconi, Riccardo↗
NASA NTRS1987

Global properties of the nearby spiral M101

M101 (NGC 5457) is a classic Sc I spiral galaxy located suffiently nearby, 6.8 Mpc, that its structure can be studied even with the coarse angular resolution of the Infrared Astronomy Satellite (IRAS). The global infrared properties of M101 are addressed including the radial dependence of its infrared emission.

Beichman, C.↗
NASA NTRS1986

Communications considerations of the very long baseline interferometry demonstration using the tracking and data relay satellite system

A desire for increased angular resolution at microwave frequencies has led to the development of radio telescopes with very lage effective apertures. Very long baseline interferometry (VLBI) has made it possible to synthesize telescopes with effective dimensions of a large fraction of an earth diameter. By using a satellite-borne radio telescope as part of a VLBI array, the dimensions of the earth cease to be a limitation. A demonstration was performed to show that the orbiting VLBI (OVLBI) concept is feasible. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting element of the VLBI demonstration. Stability tests were made before the observations to determine the suitability of the TDRSS for OVLBI use. The first successful OVLBI observations were performed using the 64-m antenna observatories of NASA's Deep Space Network in Tidbinbilla, Australia, and of the Institute for Space and Astronautical Science in Usuda, Japan in conjunction with the TDRSS.

Levy, G. S.↗
NASA NTRS1986

The advanced X-ray Astrophysics Facility (AXAF)

NASA's Advanced X-ray Astrophysics Facility (AXAF) will be an orbiting X-ray observatory, designed to address fundamental questions in astronomy and astrophysics. AXAF is the successor to NASA's second High Energy Astronomy Observatory, the Einstein X-ray Observatory, which operated from 1978 to 1981. Like the Einstein, the AXAF will be built around a grazing incidence telescope capable of forming X-ray images. AXAF, however, will go far beyond the Einstein in capability having about 10 times the angular resolution, about 100 times the sensitivity for imaging, and up to about 1000 times the sensitivity for spectroscopy. The AXAF will operate in space for 15 years, and be maintained and refurbished by use of NASA's Space Station.

Weisskopf, M. C.↗
NASA NTRS1986

Status of the very long baseline interferometry demonstration using the tracking and data relay satellite system

Very long baseline interferometry (VLBI) has been developed to the point where angular resolution at any given wavelength is limited by the dimensions of the earth. This limitation can be removed by placing a VLBI radio telescope in orbit. A demonstration of the feasibility of this approach was arranged. The Tracking and Data Relay Satellite System was used as an orbiting observatory in conjunction with the NASA Deep Space Network 64-m telescope in Tidbinbilla, Australia, and the Institute for Space and Astronautical Science 64-m antenna in Usuda, Japan. Interferometric fringes were successfully obtained from three quasars. The longest projected baseline was 1.4 earth diameters.

Levy, G. S.↗
NASA NTRS1986

The AXAF CCD imaging spectrometer

The AXAF CCD Imaging Spectrometer (ACIS) is currently being defined as a possible focal plane instrument to be flown on the Advanced X-ray Astrophysics Facility (AXAF). The imaging spectrometer consists of an array of charge coupled devices (CCD's) to be placed at the focus of the AXAF mirrors. The array will provide high angular resolution (0.5 arc seconds), moderate spectral resolution (150 eV) over the energy range 0.1 to 10 keV, temporal resolution down to 60 microseconds, and single photon quantum detection efficiencies of up to 90 percent. X-ray sensitivity for a point source exceeds 10 to the -15th ergs/sq cm sec for a 10 to the 5th sec exposure. When used in conjunction with the objective gratings, the array will yield wavelength resolution of up to 200.

Garmire, G. P.↗
NASA NTRS1986

Physical conditions near red giant and supergiant stars - An interpretation of SiO VLBI maps

Understanding the dynamical structure of circumstellar envelopes around cool giant and supergiant stars depends critically on the knowledge of what happens in the 'near zone' of the envelope, within a few stellar radii of the star. One probe with adequate angular resolution to study the near zone is VLBI observation of the SiO masers. It is shown that VLBI maps of VX Sgr establish that the particle density in the SiO masers is very high (about 10 to the 12th/cu cm), indicating that the masers form in dense cloudlets and not in a spherically expanding wind. The implications of these results for the mechanism of mass loss are discussed.

Alcock, Charles↗
NASA NTRS1986

Cryogenic star-tracking telescope for Gravity Probe B

This paper describes the design, development and preliminary testing of the cryogenic star-tracking telescope used as an optical reference for the gyroscopes in the Gravity Probe B Relativity Gyroscope experiment. The telescope is operated at 1.8 K; it is fabricated entirely from fused quartz components held together by optical contacting; it has a physical length of 14 in., a focal length of 150 in. and an aperture of 5.6 in. Readout is by two photomultiplier chopper-detector assemblies at ambient satellite temperature. When fully operational, the telescope may be expected to have a precision approaching 0.1 milliarcsec over a linear range of 70 + or 70 milliarcsec. Its projected noise performance corresponds to an angular resolution of 1 milliarcsec in 1 Hz bandwidth. The paper includes a theoretical analysis, a description of the design and fabrication of a laboratory version of the telescope, a discussion of techniques of optical contacting, an account of vibration tests on a separate mass model of the telescope, a description of the artificial star developed for optical tests, and an account of preliminary experimental results.

Everitt, C. W. F.↗
NASA NTRS1987

A CO survey of the dark nebulae in Perseus, Taurus, and Auriga

A new SIS receiver with extremely low noise temperature, used on the Columbia 1.2-m telescope has permitted mapping CO rapidly with full sampling. Results are presented of a survey for which the angular resolution of the telescope was reduced to 0.5 deg, allowing the observations for the complete region of 750 square degrees to be finished within four months, while retaining sufficient resolution to see significant substructure. Most positions with emission are in the Taurus-Auriga dark nebulae, a cloud associated with IC 348 and NGC 1333, and a cloud associated with the California nebula (NGC 1499) and NGC 1579, which overlaps the northern Taurus-Auriga nebulae but is separated from them in velocity. Also seen were several small clouds at Galactic latitude -25 deg to -35 deg southwest of the Taurus clouds, and the L1558 and L1551 clouds in the south.

Ungerechts, H.↗
NASA NTRS1987

Far-infrared detection of a circumstellar dust torus around Sharpless 106

High angular resolution scans at 42 and 95 microns have been obtained of the far-infrared source associated with S106. Using maximum entropy deconvolution techniques it is found that the far-IR-emitting dust appears to be distributed in a toroidal shape around the central star.This result is similar to the morphology implied to millimeter line and continuum mapping on a variety of size scales.

Harvey, Paul M.↗
NASA NTRS1987

A near-infrared study of the NGC 6334-IV region

High-angular-resolution, high-sensitivity maps at 1.2, 1.65, and 2.2 microns have been made of the NGC 6334-IV region. These maps show that the diffuse, bipolar 2-micron emission associated with a bipolar source in the region is probably excited by two sources between the lobes. The first is a highly obscured protostar with a luminosity of about 100,000 solar luminosities. The second possible source of excitation is the scattered free-free and bound-free emission from an H II region surrounding a second young star. The extinction to both these objects must be much higher along the line of sight from earth to them than from them to the bipolar lobes. This is consistent with an earlier interpretation of FIR observations (Harvey and Gatley, 1983) which suggested the presence of an edge-on dust disk around the two central luminosity sources. A rich cluster of lower luminosity IR sources has also been found associated with the two most luminous objects.

Harvey, P. M.↗