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NASA NTRS1984

The infrared properties of galaxy clusters - IRAS observations of the Hercules Cluster (Abell 2151)

A total of 41 sources have been detected at 60 microns to a level of 50 mJy in a 1.6 x 0.5 deg field centered on the rich galaxy cluster Abell 2151. Twenty-four of these sources can be identified with late-type spiral galaxies of estimated photographic magnitude 17 or brighter. Galaxies classified as E or S0 are notably absent in the infrared data. Within the field, eleven of the IRAS sources cannot be easily identified with galaxies in the Hercules Cluster. If the brightest 60 micron cluster source (NGC 6045) is neglected, the integral luminosity function in the far-infrared can be fitted well with two power laws of slope -1.1 and -2.5.

Young, E.↗

NASA NTRS1984

A Monte Carlo simulation of the Infrared Astronomical Satellite (IRAS) mission

The development of a Monte Carlo simulation of numerous aspects of the IRAS mission is described. The formulations used in modelling the infrared sky, the radiation environment, and the telescope are discussed. The results of running the simulation with varying mission parameters are presented.

Wolf, D. M.↗

NASA NTRS1984

Cryogenic telescope on the Infrared Astronomical Satellite (IRAS)

The Infrared Astronomical Satellite (IRAS) has completed an unbiased all-sky survey at wavelengths from 10 to 100 microns. The design and performance of the focal plane array is described with emphasis on in-orbit measurements of the sensitivity and stability. In the four broad spectral bands centered at 12, 25, 60, and 100 microns, the system noise equivalent flux density (NEFD) values are in Jy/(Square root of Hz), 0.03, 0.025, 0.046, and 0.21, respectively (Jansky = 10 to the -26th W/sq m/Hz). For point sources, a single scan at the survey rate of 3.8 arcmin/s yields limiting flux densities at the 3-sigma confidence level of 0.36, 0.30, 0.39, and 1.2 Jy. The dc stability of the junction field effect transistor (JFET) amplifiers and the excellent off-axis rejection of the telescope permit total flux measurements of extended infrared emission at levels below 6,000,000 Jy/sr. Response of the extrinsic silicon and germanium photo-detectors to ionizing radiation is described.

Low, F. J.↗

NASA NTRS1984

Detection of forbidden O I 1S-1D in comet IRAS-Araki-Alcock

Spectra of the forbidden O I 1D-3P 'red' doublet and the 1S-1D 'green' line in Comet IRAS-Araki-Alcock (1983d) were obtained during its close approach to the earth. This is the first unequivocal photoelectric detection of the green line in a cometary spectrum. The population ratio of the O (1S) state to the O (1D) state in the inner coma is not greater than 0.03. This ratio eliminates CO or CO2 and points strongly to H2O as the primary parent for excited oxygen atoms.

Cochran, W. D.↗

NASA NTRS1984

Long-term individual recovery for the IRAS mission

IRAS (Infrared Astronomical Satellite) was launched on January 25, 1983 with the primary purpose of performing an infrared survey of the entire celestial sphere. Holes were left in the main survey when some areas received less than the minimum 2-layer coverage. A second survey filled in many of these holes; however, many still required long-term individual recovery. The result was a smooth survey with 96 percent of the sky covered to the desired depth of 2 or more layers.

Lau, C. O.↗

NASA NTRS1984

Temporal and spatial behavior of the ultraviolet emissions of comet IRAS-Araki-Alcock 1983d

The spatial distribution and temporal variation of the ultraviolet emissions from comet IRAS-Araki-Alcock 1983d, observed by IUE near closest approach of the comet to the earth, suggest a model for this comet of a rotating cometary nucleus with a nonuniform distribution of volatile ices. The short lifetime of S2 (about 500 s), a species whose presence was first identified in this comet and is presumed to be present generally in the cometary ice, makes S2 a valuable indicator of short-term nuclear activity. In the case of comet 1983d, the S2 production rate decreased by a factor of 10 over a period of 28 hr.

Feldman, P. D.↗

NASA NTRS1984

The IRAS galaxy 0421+040P06: An active spiral (?) galaxy with extended radio lobes

The infrared bright galaxy 0421+040P06 detected by IRAS at 25 and 60 microns was studied at optical, infrared, and radio wavelength. It is a luminous galaxy with apparent spiral structure emitting 4 x 10 to the 37th power from far-infrared to optical wavelengths. Optical spectroscopy reveals a Seyfert 2 emission line spectrum, making 0421+040P06 the first active galaxy selected from an unbiased infrared survey of galaxies. The fact that this galaxy shows a flatter energy distribution with more 25 micron emission than other galaxies in the infrared sample may be related to the presence of an intense active nucleus. The radio observations reveal the presence of a non-thermal source that, at 6 cm, shows a prominent double lobed structure 20 to 30 kpc in size extending beyond the optical confines of the galaxy. The radio source is three to ten times larger than structures previously seen in spiral galaxies.

Beichman, C. A.↗

NASA NTRS1985

Unidentified IRAS sources: Ultrahigh luminosity galaxies

Optical imaging and spectroscopy measurements were obtained for six of the high galactic latitude infrared sources reported by Houck, et al. (1984) from the IRAS survey to have no obvious optical counterparts on the POSS prints. All are identified with visually faint galaxies that have total luminosities in the range 5 x 10 to the 11th power stellar luminosity to 5 x 10 to the 12th power stellar luminosity. This luminosity emerges virtually entirely in the infrared. The origin of the luminosity, which is one to two orders of magnitude greater than that of normal galaxies, is not known at this time.

Houck, J. R.↗

NASA NTRS1985

IRAS observations of active galaxies

The IRAS survey gives an unbiased view of the infrared properties of the active galaxies. Seyfert galaxies occupy much the same area in color-color plots as to normal infrared bright galaxies, but extend the range towards flatter 60 to 25 mm slopes. Statistically the Seyfert 1 galaxies can be distinguished from the Seyfert 2 galaxies, lying predominantly closer to the area with constant slopes between 25 and 200 mm. The infrared measurements of the Seyfert galaxies cannot distinguish between the emission mechanisms in these objects although they agree with the currently popular ideas; they do provide a measure of the total luminosity of the Seyferts. The quasar's position in the color-color diagrams continue the trend of the Seyferts. The quasar 3C48 is shown to be exceptional among the radio loud quasars in that it has a high infrared luminosity which dominates the power output of the quasar and is most likely associated with the underlying host galaxy.

Neugebauer, G.↗

NASA NTRS1984

Radioastronomical observations of comets IRAS-Araki-Alcock (1983d) and Sugano-Saigusa-Fujikawa (1983e)

Continuum and spectral-line radio observations of the comets IRAS-Araki-Alcock and Sugano-Saigusa-Fujikawa obtained at a number of observatories during May and June, 1983, are compiled in tables and briefly characterized. The species NH3, H2O, CO, and HCN are considered in detail; visible-range observations of CN are compared; and the implications of the results and the experience gained in performing and coordinating the observations for the detection of important species in other comets, especially Halley's Comet, are explored.

Irvine, W. M.↗

NASA NTRS1984

A radar study of Comet IRAS-Araki-Alcock 1983d

Radar echoes from Comet IRAS-Araki-Alcock at wavelengths 3.54 and 12.9 cm indicate that the comet's nucleus is very rough on a scale larger than the radar wavelengths; however, the low polarization ratio (25 percent at 3.54 cm) indicates that the scattering is not dominated by multiple reflections, internal reflections, or large abundances of sharp edges, cracks, and pits. The shape of the nucleus probably departs greatly from a sphere with average radii near 3-4 km. The nucleus does not appear to look significantly different from a number of Apollo and Amor asteroids except that: (1) there is a suggestion that minor structure moves rapidly across the spectra, and (2) the debris not gravitationally bound to the comet was detected, and contributes 25 percent of the total radar cross section at the 12.9-cm wavelength. Other considerations suggest that the pole was at least 45 deg away from the line of sight on two days of observation, and that the rotation period is approximately 1-2 days.

Goldstein, R. M.↗

NASA NTRS1984

Origin of the solar system dust bands discovered by IRAS

It is shown that distinctive longitudinal variations in thermal flux and mean latitude can be used to determine the typical orbits of the grains comprising the Solar System bands. In particular, how the bands should vary if they are debris associated with the three principal asteroid families is predicted. Based on these ideas, IRAS observations may allow discrimination between asteroidal and cometary origins of the dust bands and, perhaps, of the entire zodiacal cloud.

Dermott, S. F.↗

NASA NTRS1984

8- to 13-micron spectrophotometry of Comet IRAS-Araki-Alcock

Spectrophotometry between 8.0 and 13.0 microns at 2 percent spectral resolution is presented for areas in and near the nuclear condensation of Comet IRAS-Araki-Alcock (1983d) on May 11 and 12, 1983. All the spectra can be fit very well by blackbody curves, and no 10-micron silicate emissions are seen. The temperature structure of the coma suggests the presence of small (radii less than 5 microns) dust particles within 150 km of the nucleus and larger ones further out. The change in the spatial distribution of the infrared flux between the two nights suggests that an outburst may have occurred sometime on May 11.

Feierberg, M. A.↗

NASA NTRS1984

Infrared and visible detector electronics for the Infrared Astronomical Satellite (IRAS)

The paper describes the detectors, preamplifiers, and processing electronics; the system characterization test methods and results; and the performance of the detectors and electronics during the first month of on-orbit operation of the IRAS telescope. The Focal Plane Array (FPA) consists of 62 IR channels and 8 visible channels operating at 2.5 K. The IR detectors are grouped in eight 7 or 8 channel staggered linear subarrays with shared bias voltage; the visible detectors are grouped in two 4 channel skewed arrays, also with shared bias. Each channel detector is dc coupled to a TIA preamplifier through a very low power thermally isolated JFET source follower operating at about 65 K within the FPA housing. The visible channel detectors are ac coupled to TIA preamplifiers and signal chain electronics using MOSFET source followers operating at about 2.5 K within the FPA housing. The detectors, preamplifiers, analog electronics, and grounding are discussed as they evolved and were implemented during FPA retrofit, telescope integration, and preparation for launch.

Langford, D. L.↗

NASA NTRS1985

Unidentified IRAS sources - Ultrahigh-luminosity galaxies

Houck, J. R.↗

NASA NTRS1985

IUE observations of Beta Pictoris - An IRAS candidate for a proto-planetary system

The results of a preliminary analysis of high-resolution and low-resolution UV spectra of the edge-on extended-disk shell star Beta Pic, obtained with the IUE SWP and LWR instruments on November 5-6, 1984, are reported and compared with IRAS and ground-based observations. No selective UV extinction is detected, and the fine structure of the Fe II and C I absorption lines and the presence of metastable Fe II lines are considered consistent with a circumstellar nebula or extended envelope of density greater than 1000/cu cm and electron density (1-10) x 10 to the 8th/cu cm or less at 1-2 AU from the central star. The possibility that the extended orbiting disk is clumpy, as observed by Smith and Terrile (1985), is discussed.

Kondo, Y.↗

NASA NTRS1985

Seeing Comet IRAS with a radar eye

IRAS data in April 1983 held evidence for the approach of a comet which would pass close enough to earth to bounce radar signals off the cometary nucleus. The closest pass was calculated to be 450,000 km. Ephemerides were prepared for the object while radio observatory tracking schedules were arranged. S-band observations were selected for the JPL 64 m antenna to obtain 2.7 arcmin resolution. A 400 kW signal was generated. Two 4 hr observational periods were achieved, revealing a rough, faceted surface by using S-band in the first run and the X-band in the second. The comet was concluded irregularly shaped and roughly elliptical, with a 2 d period.

Jurgens, R. F.↗

NASA NTRS1985

Infrared spectrophotometry of Comet IRAS-Araki-Alcock (1983d) - A bare nucleus revealed?

Spectra of the central core and surrounding coma of Comet IRAS-Araki-Alcock (1983d) were obtained at 8-13 microns on May 11 and 2-4 microns on May 12, 1983. Spatially resolved measurements at 10 microns with a 4-arcsec beam showed that the central core was more than 100 times brighter than the inner coma only 8 arcsec away; for radially outflowing dust, the brightness ratio would be a factor of 8. The observations of the central core are consistent with direct detection of a nucleus having a radius of approximately 5 km. The temperature of the sunlit hemisphere was greater than 300 K. Spectra of the core are featureless, while spectra of the coma suggest weak silicate emission. The spectra show no evidence for icy grains. The dust production rate on May 11.4 was about 100,000 g/sec, assuming that the gas flux from the dust-producing areas on the nucleus was about 0.00001 g/sq cm per sec.

Hanner, M. S.↗