Engineering topics

Gillett, F. C.

Publications and source records attributed to Gillett, F. C..

At least 19 records

NASA NTRS1992

Infrared observations and thermal models of the Beta Pictoris disk

Measurements of the flux from the central portion of the Beta Pic disk performed via photometry at 3.5-20 microns in 4- and 8-arcsec apertures are presented. The 10.1- and 20-micron measurements show an excess which is extended, with significant flux located in the annulus between 4- and 8-arcsec diameter centered on the star. Disk models are calculated to reproduce the ground-based IR data, IRAS fluxes, IRAS 60-micron scan profile widths, and optical scattered light distribution. The color temperature and angular scale of the disk are found to be inconsistent with emission from large ('blackbody') particles: most of the thermal emission originates from particles which are inefficient radiators, with sizes near 1 micron. A simple disk with a single power-law spatial distribution is inconsistent with the combined optical and IR data. The inner disk component represents a gross deficit of material relative to an inward extrapolation of the outer component.

Backman, D. E.↗

NASA NTRS1990

The nature of unidentified 12 micron IRAS sources at high Galactic latitudes

A sample of 47 previously uncatalogued objects located above a Galactic latitude of 50 deg, and detected at 12 microns by the IRAS, is studied using near-infrared photometry. Ground-based observations show that the objects consist primarily of late-type M giant stars with long-wavelength excesses probably due to emission from dust associated with mass loss. The sample contains one oxygen-rich giant star undergoing rapid mass loss; an extremely cool (1230 K) carbon star 12560-1656 that may be as far as 10 kpc away; and a luminious quasar 13349-2438. The absence of nearby, low-luminosity infrared sources in this sample limits the space density of field brown dwarf stars. The fact that almost all the IRAS 12 micron sources have stellar counterparts visible on both the red and blue Palomar Observatory Sky Survey prints provides a tool for discriminating ordinary red stars.

Beichman, C. A.↗

NASA NTRS1989

The peculiar planetary nebula in M22

The source discovered by the IRAS satellite near the center of the globular cluster M22, IRAS 18333-2357, has been studied using the IUE satellite and a ground-based optical telescope. The northern component of the close pair of stars is not a member of the cluster. The southern component is a hot star with T(eff) of about 50,000 K illuminating a small planetary nebula and is a member of M22. Both the planetary nebula and its central star are extremely hydrogen deficient. The luminosity of the central star is in good agreement with that expected on theoretical grounds and with the observed luminosity of the tip of the red giant branch.

Cohen, J. G.↗

NASA NTRS1989

IRAS 20460+1925 - An extreme Seyfert 2 and one of the most luminous galaxies known

The properties of IRAS 20460+1925, which is identified with a Seyfert 2 galaxy at z = 0.181, are described. The object is dominated by an unresolved nucleus embedded in a region of extended emission with a diameter of 35 kpc. The bolometric luminosity of the galaxy is 7 x 10 to the 12 solar luminosities, and the FWHM of the forbidden and permitted lines is between 1700 and 2100 km/s in the rest frame. The 0.5-3.5 micron energy distribution of IRAS 20460+1925 is among the reddest known for any type of galaxy, while its 12-100 micron flux distribution is among the flattest known for an extragalactic source. There is no evidence for starlight in its spectrum. The reddened hot thermal and nonthermal emission from the nucleus dominates at shorter wavelengths while hot dust contributes to the longer wavelengths.

Frogel, Jay A.↗

NASA NTRS1989

The optical/infrared counterpart(s) of IRAS 18333-2357

Observations of the potential optical counterparts of the unusual source IRAS 18333-2357 are reported. There are three distinct optical objects located within roughly 2 arcsec of the IR source: a red star, a very blue star, and an extended emission line nebulosity. IRAS 18333-2357 indeed appears to be physically associated with the Galactic globular cluster M22, and while it probably should be considered a PN, its very small nebular mass and extreme abundance anomalies are very unusual among known PNe. IRAS 18333-2357 does not appear to be at an early stage of PN evolution, but instead may be in a late stage. The lack of an associated radio or H-alpha source is the result of abundance anomalies in the source.

Gillett, F. C.↗

NASA NTRS1987

Physical processes and infrared emission from the Cassiopeia A supernova remnant

IRAS 12-100 micron data on the Cas A remnant are presented, and various physical mechanisms and astrophysical sites that may contribute to the observed infrared emission are analyzed. The contributions of various sources of infrared emission to the IRAS fluxes are found to be small. The residual infrared emission is attributed to thermal emission from dust which is swept up by the expanding supernova blast wave and collisionally heated by the postshock X-ray emitting gas. The calculations are consistent with a shock velocity of 1800 km/s and a preshock gas density of about 2/cu cm. The mass of the swept-up gas is about 0.6 solar mass. An excess of 12 micron thermal emission in the spectrum of Cas A suggests the presence of very small particles in the preshocked gas.

Dwek, E.↗

NASA NTRS1986

IRAS observations of R Coronae Borealis - Detection and study of a fossil shell

IRAS observations of the extreme hydrogen-deficient supergiant R CrB are presented and discussed. The star is surrounded by an enormous cool dust cloud which is tentatively identified as a fossil remnant of the hydrogen-rich envelope of the star. The angular extent of the emission corresponds to a linear extent of 8 pc, 20 times larger than the largest previously known shell around a late-type star. The radiating material is distributed very symmetrically over a wide range of radial distances from the star. The dust temperature is nearly constant throughout the extended shell. The total mass in the shell is about 0.3 solar mass. The ejection process appears to have occurred in a spherically symmetric fashion with a nearly constant mass loss rate and expansion velocity over a period of about 150,000 yr, terminating about 26,000 yr ago.

Gillett, F. C.↗

NASA NTRS1986

IRAS observations of the nuclear bulge of M31

IRAS observations of the nuclear bulge of M31 are reported. The 12-micron and 25-micron emission is attributed to circumstellar dust emission from late-type stars, while the 60 and 100-micron emission is attributed to interstellar dust emission. The total input rate of circumstellar gas and dust into the interstellar medium is estimated to be 0.015 solar masses/yr. The mass of dust in the interstellar medium estimated from the far-infared flux is about 1500 solar masses. The color temperature of the far-infrared-emitting dust is 45 K. The time required to accumulate the observed mass in interstellar dust is about 10 million yr. Either supernova-generated winds or star formation can deplete this gas without violating the observations.

Soifer, B. T.↗

NASA NTRS1986

IRAS observations of a small sample of blue irregular galaxies

IRAS satellite IR observations are presently used to investigate the properties of the dust in a small sample of irregular galaxies chosen to cover a wide range in levels of star formation activity. The irregulars are found to have comparatively normal IR properties; the only exception is NGC 1569, an irregular galaxy with intense global star formation which seems to have a larger dust fraction at temperatures whose energies peak at 25-60 microns, by comparison with other irregulars. DDO 47, the system with lowest star formation activity, has the lowest far-IR color temperature and highest ratio of IR to H-alpha flux; this is suggested to be due to the decreased importance of radiation from young stars in heating the dust.

Hunter, D. A.↗

NASA NTRS1986

IRAS 18333-2357 - An unusual source in M22

The present paper is concerned with a search for IRAS sources positionally associated with globular clusters. This search revealed a strong source with unusual infrared colors, IRAS 18333-2357, near the center of M22. M22 (NGC 6566) is a bright, nearby, metal-poor globular cluster. Attention is given to the observations, the mass and luminosity of IRAS 18333-2357, the mass-loss rate, and the nature of IRAS 18333-2357. It is concluded that IRAS 18333-2357 may possibly be a bipolar nebula similar to OH 0739-14 although element abundance arguments appear to favor a carbon-rich rather than oxygen-rich shell.

Gillett, F. C.↗

NASA NTRS1985

Epsilon Aurigae during eclipse - IRAS observations of the cool secondary component

Measurements of Epsilon Aur made from 5 to 60 microns over a period of less than 1 month during full eclipse, including special Infrared Astronomy Satellite (IRAS) observations at 12, 25, and 60 microns are presented. The observed flux at 60 microns agrees well with a prediction based on ground-based infrared monitoring of the eclipse ingress in 1982. Fits to the flux in excess of simple models for the primary star's infrared photospheric continuum yield T = 475 + or - 50 K, Omega = 8.6 + or - 1.0 x 10 to the -16th sr for the secondary. The total observed luminosity from the secondary is no larger than 50 solar luminosities.

Backman, D. E.↗

NASA NTRS1984

SIRTF: The next step

The scientific and technical background and prospects for the space infrared telescope facility (SIRTF) are described. This facility is a superfluid-helium-cooled, 0.85-meter infrared telescope to be placed in orbit in 1993. It is designed to carry out photometry over the wavelength range 2 to 700 micrometers, and diffraction-limited imagery in either broad or narrow spectral bands over the range 1.8 to 200 micrometers. It is proposed that SIRTF measure spectra in the range 2.5 to 200 micrometers with resolving power between 50 and 1000 and that the focal plane contain about 20,000 detector elements, both discrete and in arrays. The SIRTF observatory is designed to be a long-lived facility providing opportunities for general investigations by the entire scientific community. For following up the all-sky survey carried out by the Infrared Astronomical Satellite (IRAS), SIRTF is ideal. It can do a deep survey to flux levels 5000 times fainer than IRAS and can obtain spectra of even the faintest IRAS sources.

Gillett, F. C.↗

NASA NTRS1984

SIRTF: the Next Step

The space infrared telescope facility (SIRTF) is a 1-meter class, long duration, super fluid helium-cooled telescope in Earth orbit, equipped with imaging and spectroscopic instrumentation operating over the wavelength range from 1.8 to 700 microns. The SIRTF will be the most powerful tool available for studying many of the compelling problems in contemporary astrophysics and for further exploration of the infrared sky demonstrated by IRAS. Adaptation of IRAS technology (cryogenics, optics, and pointing and guidance) is discussed.

Gillett, F. C.↗

NASA NTRS1984

Early results from the Infrared Astronomical Satellite

The discoveries made with the Infrared Astronomical Satellite (IRAS) are reviewed. Findings on large-scale extended infrared emission associated with the solar system and the Galaxy and medium-scale extended infrared emission associated with zodiacal dust bands and infrared cirrus clouds are described. Comets have been found to be much dustier than previously thought. Solid material orbits Vega and other stars, and emission from cool interstellar material has been traced throughout the Galaxy up to the poles. Stars in the process of formation have been detected. The far-infrared sky away from the galactic plane has been found to be dominated by spiral galaxies, some of which emit more than 50 percent and as much as 98 percent of their energy in the infrared.

Neugebauer, G.↗

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

IRAS observations of the diffuse infrared background

IRAS data reveal bright emission from interplanetary dust which dominates the celestial background at 12, 25, and 60 microns except near the galactic plane. At 100 microns, interplanetary dust emission is prominent only near the ecliptic plane; diffuse galactic emission is found over the rest of the sky. At the galactic poles, the observed brightness implies that A(v) is likely to be of order 0.1 mag. The angular variation of the zodiacal emission in the ecliptic plane and in the plane at elongation 90 deg, and an annual modulation of the ecliptic pole brightness, are generally consistent with previously determined interplanetary dust distributions.

Hauser, M. G.↗

NASA NTRS1984

Infrared cirrus - New components of the extended infrared emission

Extended sources of far-infrared emission superposed on the zodiacal and galactic backgrounds are found at high galactic latitudes and near the ecliptic plane. Clouds of interstellar dust at color temperatures as high as 35 K account for much of this complex structure, but the relationship to H I column density is not simple. Other features of the extended emission show the existence of warm structures within the solar system. Three bands of dust clouds at temperatures of 150-200 K appear within 10 deg on both sides of the ecliptic plane. Their ecliptic latitudes and derived distances suggest that they are associated with the main asteroid belt. A third component of the 100-micron cirrus, poorly correlated with H I, may represent cold material in the outer solar system or a new component of the interstellar medium.

Low, F. J.↗

NASA NTRS1984

Discovery of a shell around Alpha Lyrae

IRAS observations of Alpha Lyrae reveal a large infrared excess beyond 12 microns. The excess over an extrapolation of a 10,000 K blackbody is a factor of 1.3 at 25 microns, 7 at 60 microns, and 16 at 100 microns. The source of 60 microns emission has a diameter of about 20 arcsec. This is the first detection of a large infrared excess from a main-sequence star without significant mass loss. The most likely origin of the excess is thermal radiation from solid particles more than a millimeter in radius, located approximately 85 AU from Alpha Lyr and heated by the star to an equilibrium temperature of 85 K. These results provide the first direct evidence outside of the solar system for the growth of large particles from the residual of the prenatal cloud of gas and dust.

Aumann, H. H.↗