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  • ASTRONOMY  (513)
  • SOLAR PHYSICS
  • 1980-1984  (813)
  • 1970-1974  (52)
  • 1
    Publication Date: 2014-09-18
    Description: A liquid-helium-cooled grating spectrometer (CGS) is being developed as a facility instrument for the Kuiper Airborne Observatory (KAO), primarily to study for infrared lines originating in the interstellar medium. A maximum resolving power of approximately 6000 is achieved by means of a 45 cm long Echelle grating and is optically capable of operating in the spectral range from 25 to 300 microns. An array of detectors is used to simultaneously measure a line and the adjacent continuum from astronomical sources. Currently six detectors allow measurements in the 30 to 120 micron spectral band. The instrument, its operation, and its performance are described.
    Keywords: ASTRONOMY
    Type: Airborne Astron. Symp.; p 313-319
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  • 2
    Publication Date: 2019-06-28
    Description: VLBI 2.3 GHz observations of a strong radio flare of the binary star system Circinus X-1 indicate a radio source flaring component angular size of 0.0015-0.015 arcsec. This is equivalent to a linear size of 15-150 AU at the 10 kpc distance of Circinus X-1, although interstellar medium scattering may have enlarged the apparent angular source size. Since the radio source quiescent component, observed prior to the flare, had an angular size greater than 0.2 arcsec (equivalent to more than 2000 AU at 10 kpc), the quiescent radio emission comes from a region much larger than that proposed in recent models for Circinus X-1. The quiescent component appears to be variable on a time scale of years, and is probably fueled by the Circinus X-1 binary system.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 268; May 1
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  • 3
    Publication Date: 2019-06-28
    Description: VLBI observations of the nucleus of Centaurus A made at 2.3 GHz on baselines with minimum fringe spacings of 0.15 and 0.0027 arcsec are presented. Results show that the nuclear component is elongated with a maximum extent of approximately 0.05 arcsec which is equivalent to a size of approximately 1 pc at the 5 Mpc distance of Centaurus A. The position angle of the nucleus is found to be 30 + or - 20 degrees, while the ratio of nuclear jet length to width is less than or approximately equal to 20. The nuclear flux density is determined to be 6.8 Jy, while no core component is found with an extent less than or approximately equal to 0.001 (less than or approximately equal to 0.02 pc) with a flux density of greater than or approximately equal to 20 mJy. A model of the Centaurus A nucleus composed of at least two components is developed on the basis of these results in conjunction with earlier VLBI and spectral data. The first component is an elongated source of approximately 0.05 arcsec (approximately 1 pc) size which contains most of the 2.3 GHz nuclear flux, while the second component is a source of approximately 0.0005 arcsec (approximately 0.01 pc) size which is nearly completely self-absorbed at 2.3 GHz but strengthens at higher frequencies.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 266
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  • 4
    Publication Date: 2019-06-28
    Description: The 3P1 - 3P2 fine structure line emission from neutral atomic oxygen at 63 microns in the vicinity of the galactic center was mapped. The emission is extended over more than 4' (12 pc) along the galactic plane, centered on the position of Sgr A West. The line center velocities show that the O I gas is rotating around the galactic center with an axis close to that of the general galactic rotation, but there appear also to be noncircular motions. The rotational velocity at R is approximately 1 pc corresponds to a mass within the central pc of about 3 x 10(6) solar mass. Between 1 and 6 pc from the center the mass is approximately proportional to radius. The (O I) line probability arises in a predominantly neutral, atomic region immediately outside of the ionized central parsec of out galaxy. Hydrogen densities in the (O I) emitting region are 10(3) to 10(6) cm(-3) and gas temperatures are or = 100 K. The total integrated luminosity radiated in the line is about 10(5) solar luminosity, and is a substantial contribution to the cooling of the gas. Photoelectric heating or heating by ultraviolet excitation of H2 at high densities (10(5) cm(-3)) are promising mechanisms for heating of the gas, but heating due to dissipation of noncircular motions of the gas may be an alternative possibility. The 3P1 - 3P0 fine structure line of (O III) at 88 microns toward Sgr A West was also detected. The (O III) emission comes from high density ionized gas (n 10(4) cm(-3)), and there is no evidence for a medium density region (n 10(3) cm(-3)), such as the ionized halo in Sgr A West deduced from radio observations. This radio halo may be nonthermal, or may consist of many compact, dense clumps of filaments on the inner edges of neutral condensations at R or = 2 pc.
    Keywords: ASTRONOMY
    Type: NASA-CR-166510 , NAS 1.26:166510
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  • 5
    Publication Date: 2019-06-28
    Description: Time delay and fringe frequency measurements at 2.29 GHz have been obtained with VLBI on baselines of about 10,000 km, in order to determine the positions of milliarcsec nuclei in 207 extragalactic radio sources. Accuracy ranges are estimated to lie between 0.1 and 1.0 arcsec in both right ascension and declination, with all sources having uncertainties of less than 4 arcsec in both coordinates. These sources constitute part of an all-sky VLBI catalog of milliarcsec radio sources, for 752 of which arcsec positions have thus far been determined.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 88; Aug. 198
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  • 6
    Publication Date: 2011-08-17
    Description: The Voyager IR investigation is described, which uses a Michelson interferometer in the 180-2500/cm range, and a single-channel radiometer for the visible and near-IR, sharing a 50-cm diameter telescope. Emphasis is placed on the differences between the Voyager and the previous designs, including reductions in the field of view and in the noise equivalent spectral radiance of the instrument. Attention is given to the optical layout, the electronics module, power supply placement, thermal control heaters and flash heaters, data reduction, and calibration. A sample spectrum of Jupiter is also discussed.
    Keywords: ASTRONOMY
    Type: Applied Optics; 19; May 1
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  • 7
    Publication Date: 2011-08-18
    Description: A decrease in the solar radius is determined using the technique of Dunham and Dunham (1973), in which timed observations are made just inside the path edges. When the method is applied to the solar eclipses of 1715, 1976, and 1979, the solar radius for 1715 is 0.34 + or - 0.2 arc second larger than the recent values, with no significant change between 1976 and 1979. The duration of totality is examined as a function of distance from the edges of the path. Corrections to the radius of the sun derived from observations of the 1976 and 1979 eclipses by the International Occultation Timing Association are also presented.
    Keywords: SOLAR PHYSICS
    Type: Science; 210; Dec. 12
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  • 8
    Publication Date: 2011-08-18
    Description: A balloon-borne, 1.2 meter Cassegrain telescope with a servo-controlled chopping secondary mirror has been developed and used to survey the Galactic Plane at submillimeter wavelengths. The telescope pointing system uses a gyroscope as the primary stabilization reference and makes use of microprocessors for pointing control, on-board data collection, and telemetry formatting. A description of the telescope, multi-channel liquid-helium-cooled focal plane and the aspect and orientation subsystems are presented.
    Keywords: ASTRONOMY
    Type: (ISSN 0273-1177)
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  • 9
    Publication Date: 2011-08-18
    Description: VLBI and CCD astrometry is presented which establishes the coincidence of the X-ray and radio object Cir X-1 with an object lying about one arcsec south of the object 'L' of Whelan et al. (1977), a conclusion reached previously by Argue and Sullivan (1982). The question whether the object L has any physical connection with Cir X-1 cannot yet be definitely answered.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 209; 11P-14P
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  • 10
    Publication Date: 2011-08-18
    Description: Observations of the 691-GHz (J = 6-5) transition of CO in the BN/KL region of Orion obtained in February 1981, at the IR Telescope Facility at Mauna Kea are reported. The system employs a heterodyne receiver with an overall noise temperature of 3900 K DSB at 432 microns, 64 5-MHz IF-filter-bank channels, and a chopping secondary with 120-arcsec excursion, and has 35-arcsec resolution. Sample data are presented graphically and analyzed using a rate equation and a kinetic model. A 35 x 45-arcsec core with hot broad plateau emission (antenna temperature 180 + or - 36 K) surrounded by an area of strong narrow-line 120-K emission is found. It is suggested that the plateau emission originates in a wide thin sheet after a shock wave, with H2 density at least 10 to the 6th/cu cm and gas kinetic temperature greater than 500 K.
    Keywords: ASTRONOMY
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