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NASA NTRS1986

Discovery of an infrared-loud quasar

The IRAS source 13349 + 2438 is a quasar with a redshift of z = 0.107, broad (15,000 km/s) emission lines and a luminosity of 2.7 x 10 to the 12th solar luminosity, emitted mostly between 4.8 and 12 microns. The object, a weak radio source, is the first previously unidentified quasar selected through its infrared emission and is the prototype radio-quiet, infrared-bright quasar. A dusty interstellar medium may be responsible for the infrared emission as well as for quenching the visual emission and attenuating the radio emission from the central energy source.

Beichman, C. A.↗

NASA NTRS1987

Detection of interstellar CH in the far-infrared

The first astronomical detection of CH in the far-infrared has been made. A ground state of rotational transition was observed in absorption against the far-infrared continuum peak of Sgr B2. The lines are resolved at a velocity resolution of 62 km/s, have a line width of roughly 250 km/s, and a line center optical depth of about 0.29. The inferred total column density of CH in the ground state along the line of sight is roughly 1.6 x 10 to the 15th/sq cm. Comparison of the far-infrared profiles to the 3 GHz emission lines confirms that the ground-state Lambda-doublet levels are inverted and gives an accurate estimate of the excitation temperature. The excitation temperature of the 3264 MHz line varies from cloud to cloud along the line of sight, the levels being most inverted in the Sgr B2 molecular cloud. The large intensity of the 3264 MHz line in this cloud relative to other clouds along the line of sight may thus be primarily an excitation effect.

Stacey, Gordon J.↗

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 NTRS1987

Infrared emission and star formation in early-type galaxies

Infrared emission from elliptical and S0 galaxies was studied to determine the extent of low-mass star formation in such early-type galaxies. It is found that the infrared colors of about one-third of the sample are consistent with ongoing star formation, although a contribution to the emission from an 'active' nucleus might play an important role in some objects. Apparently star formation has not ceased in some elliptical and S0 galaxies and may be fueled by mass loss from evolved stars or out of the rubble of galaxian mergers. Of four plausible candidate star-forming ellipticals, three show evidence for accretion and/or merger. It is also concluded that IRAS two-color diagrams are often ambiguous in determining whether or not emission arising from star formation dominates far-infrared luminosity.

Thronson, Harley A., Jr.↗

NASA NTRS1988

Stand For Infrared Multiple-Internal-Reflection Mount

Infrared MIR spectra more reproducible, and MIR crystal suffers less damage. Technique prevents lateral movement between elements in multiple-internal-reflection (MIR) cell during assembly. Reproducibility of infrared MIR spectra relies on ability to maintain condition of crystal, which is MIR element, and to control contact between crystal and sample. Cell used in infrared spectroscopy.

Long, Edward R., Jr.↗

NASA NTRS1988

Calculation of space station infrared irradiance from atmosphere-induced emissions

The excitation mechanisms and radiance estimates over the 1 to 10 micron region for CO2(v), H2O(v), CO(v), OH(v), NO2(2B-2A) and N2(B3 pi - A3 sigma) are discussed. The infrared irradiance of the Space Station at an altitude of 460 km was estimated. The surface material was presumed to be non-carbonaceous and inert. The determined number densities of the various gases relevant to the Space Station from both ambient and outgassing sources are presented. A model for the production of and emission from the infrared active molecules was constructed that considers two classes of production processes: (1) gas phase excitation of molecules in the near Station environment by collision with ambient flux; and (2) surface processes that lead to molecular excitation. A composite spectrum of all major emitting species shows that the observed irradiance is non-uniform over the 1 to 8 micron region. The comparison of predicted irradiance with the zodiacal background indicates that the Space Station infrared background from atmosphere-induced emissions may be a problem of consequence.

Fraser, M. E.↗

NASA NTRS1987

Determination of cloud ice water content and geometrical thickness using microwave and infrared radiometric measurements

Cloud ice water content and cloud geometrical thickness have been determined using a combination of near-infrared, thermal infrared and thermal microwave radiometric measurements. The radiometric measurements are from a Multispectral Cloud Radiometer, which has seven channels ranging from visible to thermal infrared, and an Advanced Microwave Moisture Sounder, which has four channels ranging from 90 to 183 GHz. Studies indicate that the microwave brightness temperatures depend not only on the amount of ice water content but also on the vertical distribution of ice water content. Studies also show that the low brightness temperature at 92 GHz for large ice water content is due to cloud reflection which reflects most of the irradiance incident at the cloud base downward. Therefore the 92 GHz channel detects a low brightness temperature at the cloud top.

Wu, Man-Li C.↗

NASA NTRS1987

Far-infrared continuum emission from the nucleus, starburst, and extended spiral arms of NGC 1068

Far-infrared slit scans across NGC 1068 are used to better define the contribution of the active nucleus, starburst disk, and extended spiral arms in the luminous output of this bright Seyfert 2 galaxy. The decomposition of the emission from the bright, inner 3 kpc of this galaxy suggests that at 50 microns, about half the emission is from star formation in a starburst disk and half from the compact, centrally heated circumnuclear cloud. The 100-micron profile of the starburst disk is asymmetric with respect to the nucleus. This appears to be the result of an extraordinary star-forming complex about a kiloparsec away from the center. With the application of maximum entropy deconvolution to the scans, evidence is found for 100-micron emission from the extended spiral arms of the galaxy. The far-infrared emission from the starburst region is distinguished from that of the extended spiral arms. In terms of both total luminosity and surface brightness, the extended spiral arms of NGC 1068 are at the bright end of the range of far-infrared emission from quiescent, noninteracting spirals.

Lester, D. F.↗

NASA NTRS1987

Sub-Doppler tunable far-infrared spectroscopy

The first experimental observations of sub-Doppler linewidths in a cell made using tunable far-infrared radiation are reported. A double-resonance scheme has been used, combining CO2-laser infrared radiation with tunable far-infrared radiation to observe a sub-Doppler line shape in an excited vibrational state of CH3OH.

Inguscio, M.↗

NASA NTRS1987

The infrared diagnostic of a dusty plasma with applications to supernova remnants

IRAS observations of infrared emission from supernova remnants constitute the first observational evidence of shock-heated dust in the interstellar medium. These observations can provide valuable information on the morphology of supernova remnants, and on their interaction with the ambient interstellar medium. In particular, they can be used to study the physical condition and the cooling rate of dusty astrophysical plasmas. In this paper, consideration is given to the possibilities and limitations of using the infrared observations as a diagnostic for the shocked gas, and as a means of determining remnant parameters. The paper presents improved calculations for the cooling rate of a dusty plasma by means of gas-grain collisions, and the equilibrium temperature of the dust for a variety of plasma conditions. These results are then used to define the density-temperature parameter space of the plasma, which, given its infrared spectrum, should be occupied by the observed remnant. This constraint can be used to estimate distances to supernova remnants and to set limits on various parameters that determine their evolution. The analysis is applied to the remnants Cas A and the Cygnus Loop.

Dwek, Eli↗

NASA NTRS1987

Far-infrared variability in active galactic nuclei

Pointed IRAS observations of 20 active galaxies were examined in the first detailed search for far-infrared variability in a large sample of active galaxies. Less extensive survey data were also checked for evidence of strong 6-month variability in 45 active galaxies. The far-infrared fluxes of three highly polarized objects ('blazars') appeared to vary by up to a factor of 2 on time scales of a few months. No convincing cases of variability greater than about 15 percent (rms) were found in any of the normal quasars or Seyfert galaxies studied. It appears that blazars tend to be variable at all wavelengths, but most active galaxies may be systematically less variable in the far-infrared than at higher frequencies.

Edelson, R. A.↗

NASA NTRS1988

Infrared radiative transfer in dense disks around young stars

A two-dimensional radiative transfer program has been used to determine the temperature distribution within cylindrically symmetric, centrally heated dust clouds. In particular, the disk-shaped structures observed around young luminous stars have been modeled. Changing the dust distribution in these disks primarily affected the observed morphology in the near-infrared and far-infrared, and at millimeter wavelengths. The overall cloud spectrum, however, was mainly determined by the characteristics of the grains themselves. Comparison with published far-infrared and molecular line data has indicated that the dust density can generally be modeled by a power-law distribution in r with index of -2 and an exponential in z with disk thickness proportional to 1/r. When observed nearly edge-on, scattered direct stellar radiation is observed in the polar regions in the form of comet-shaped lobes of emission.

Dent, William R. F.↗

NASA NTRS1988

The universe at infrared wavelengths

This article discusses the status of infrared astronomy after the mission of the Infrared Astronomical Satellite (IRAS). Important scientific results from IRAS include: the origin of the interplanetary dust cloud, the formation of solar type stars, the energetics of the interstellar medium, the discovery of ultra-luminous infrared galaxies and their possible relation to the origin of quasars, and the large scale structure of the universe.

Beichman, C. A.↗

NASA NTRS1988

Investigation of PTFE transfer films by infrared emission spectroscopy and phase-locked ellipsometry

When a PTFE sheet was rubbed unidirectionally over a smooth surface of stainless steel an essentially monomolecular transfer film was formed. by ellipsometric and emission infrared spectroscopic techniques it was shown that the film was 10 to 15 A thick and birefringent. From the intensity differences of infrared bands obtained with a polarizer passing radiation polarized in mutually perpendicular planes, it was possible to deduce transfer film orientation with the direction of rubbing. After standing in air for several weeks the transfer films apparently increased in thickness by as much as threefold. At the same time both the index of refraction and the absorption index decreased. Examination of the surfaces by optical and electron microscopies showed that the films had become porous and flaky. These observations were consistent with previous tribological measurements. The coefficients of friction decreased with the formation of the transfer film but increased again as the film developed breaks. The applicability of the ellipsometric and polarized infrared emission techniques to the identification of monomolecular tribological transfer films of polymers such as PTFE has been demonstrated.

Lauer, James L.↗

NASA NTRS1987

Time- and position-varying infrared scene simulation

Rapidly changing infrared scenes can be generated as a function of position using thermally produced irradiance. This can be done most conveniently by using a variable dwell-time, variable diameter, and scanning laser beam to deposit a predetermined amount of laser energy, as a function of position, on the target surface. An infrared target simulator has been designed and tested to perform within stringent temperature simulation requirements: heating rate of over 100 K/sec is achieved, and temperature gradients of 200 K/mm can be maintained. Problems with heat transfer between adjacent elements at different temperatures are solved by modeling the thermal layer on the target surface as a low-pass filter, which cuts off all the frequencies above the thermal cutoff frequency. When the system approach is taken to the infrared simulation design, the optical system limited performance results in the best realizable performance. In this case, the thermal layer on the target surface is designed so that the thermal cutoff frequency is above the optical cutoff frequency.

Scholl, Marija S.↗

NASA NTRS1988

Small-aperture infrared photometry of Seyfert 1 galactic nuclei

Multiaperture infrared photometry of the nuclei of five Seyfert 1 galaxies is presented. When apertures approaching the seeing limit were used, it was found that all of the nuclei have observed power law energy distributions with F(nu) proportional to 1/nu sq from 1.25 to 3.45 micron. After correcting for reddening, the spectral indices had a range of alpha = 1.4-1.9. These results are supported through infrared imaging of one of the program galaxies, and they demonstrate the importance of properly isolating the nuclear component from the stellar disk through the use of extremely small apertures. Although the nature of the infrared emissions cannot be determined, results indicate that a common energy source exists among the observed galaxies.

Simons, D. A.↗

NASA NTRS1988

Near-infrared line and continuum emission from the blue dwarf galaxy II Zw 40

A multicolor analysis of new near-infrared line and continuum measurements indicates that nebular recombination emission and photospheric radiation from young blue stars produce most of the near-infrared continuum emission in the central 6 arcsec of the dwarf galaxy II Zw 40. The derived nebular recombination level is in excellent agreement with independent observations of the radio free-free continuum. It is found that evolved stars, which dominate the near-infrared emission from normal galaxies, contribute no more than 25 percent of the total 2.2 micron flux in the central region of II Zw 40. It is concluded that the total mass of the evolved stellar population in the central 400 pc of the galaxy is less than about two hundred million solar. The total mass of recently formed stars is about two million solar, and the stellar mass ratio is exceptionally large. Thus, II Zw 40 is a quintessential starburst galaxy.

Joy, Marshall↗

NASA NTRS1988

Hard X-ray observations of ultraluminous infrared galaxies

X-ray flux upper limits of 2-10 keV for ultraluminous infrared galaxies were drawn from the HEAO A-1 data base. The hard X-ray luminosities of these sources are much weaker relative to their total luminosities than would be expected for Seyfert 1 galaxies or quasi-stellar objects. Because of the low level of interstellar extinction for hard X-rays, this result suggests that the ultraluminous galaxies are not powered by embedded QSOs that are otherwise similar to other QSOs. Three other possibilities are: (1) the infrared galaxies may contain a form of X-ray-quiet active nucleus; (2) the X-ray sources in active nuclei may not turn on until after the circumnuclear gas has cleared; or (3) the bulk of the infrared luminosity in these galaxies may be generated by intense circumnuclear star formation.

Rieke, G. H.↗