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Harper, D. A.

Publications and source records attributed to Harper, D. A..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The energetics and mass structure of regions of star formation: S201

Theoretical predictions about dust and gas in star forming regions are tested by observing a 4 arcmin region surrounding the radio continuum source in 5201. The object was mapped in two far infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in 5201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far infrared emitting grains, equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources.

Thronson, H. A., Jr.↗
NASA NTRS1984

W3 North: Far-infrared and radio molecular observations

The W3 North (G133.8 + 1.4) source is the northernmost member of a string of active star forming regions that marks the western boundary of the giant HII region W4. Far infrared and radio observations of molecular CO were made of the W3 star forming region. The W3 North object shows extended dust and gas emission which suggests a fairly advanced disruption of a molecular cloud. An estimate of the age of the embedded HII region is given, and emission maps of the W3 object are presented. The W3 North source may be the oldest object among the W3 complex of sources.

Thronson, H. A., Jr.↗
NASA NTRS1984

NGC 2024 - Far-infrared and radio molecular observations

New far-infrared continuum and millimeter-wave molecular observations of NGC 2024 are presented. The measurements were obtained at relatively high angular resolution making it possible to describe the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north-south direction and centered on the dark lane that is seen in visual photographs. The maps of the source using the 'high-density' molecules CS and HCN confirm this picture and makes it possible to describe the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1 arcmin south of the bright mid-infrared source IRS 2. The data presented here, along with other observations, make it possible to describe a model for the source.

Thronson, H. A., Jr.↗
NASA NTRS1984

The energetics and mass structure of regions of star formation - S201

Theoretical predictions about dust and gas in star-forming regions are tested by observing a 4-arcmin region surrounding the radio continuum source in S201. The object was mapped in two far-infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in S201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far-infrared emitting grains, a equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources.

Thronson, H. A., Jr.↗
NASA NTRS1983

Far-infrared observations of the type 1 Seyfert galaxy NGC 4051

The Kuiper Airborne Observatory was used, together with a seven-element array, in measurements of the far-IR flux from the Seyfert galaxy NGC 4051. Flux densities within and outside of the central region were found to be comparable, with a possible local peak of emission in the west, and a total far-IR luminosity of 3.4 + or - 0.8 billion solar luminosities. The spectral shape of the radiation and its extended distribution, together with data at other wavelengths, suggest that the IR emission arises from warm dust. The relatively weak IR flux, and the apparent lack of dust and gas by comparison to the total (virial) material, indicate less active star formation than that found in such galaxies as the type 2 Seyfert, NGC 1068.

Smith, H. A.↗
NASA NTRS1983

Far-infrared detection of low-luminosity star formation in the Bok globule B335

Measurements of far-infrared intensities in the Bok globule B335, made with higher spatial and spectral resolution than two earlier studies, are described. The NASA 3-m Infrared Telescope Facility was used in February 1981 and the Kuiper Airborne Observatory 0.9-m telescope was used in October 1981 and August 1982 for the observations. The far-infrared source in B335 was revealed to be more compact than previously assumed, ruling out the interstellar radiation field as the dominant heat source. The new far-infrared size, luminosity, and temperature derived suggest that these may be the first observations of low-mass star formation embedded deeply within a Bok globule. The far-infrared source does not have a near-infrared or radio continuum counterpart. High angular resolution at submillimeter wavelengths will be critical in further studies of low-mass star formation.

Davidson, J. A.↗
NASA NTRS1983

Millimeter and submillimeter observations of 3C 273

The first detection of 3C 273 (1226 + 023) at wavelengths of 107, 240, and 400 microns together with contemporary measurements at 800 microns, 1.1, 1.9, 3.3, and 8.9 mm, is reported. These observations show that the continuum spectrum of 3C 273 can be extrapolated smoothly from the submillimeter to the infrared with a constant spectral index. There is no evidence of thermal emission from dust. It is shown that the spectrum is consistent with optically thin synchrotron emission from a relativistic beam at a small angle to the line of sight.

Glaccum, W.↗
NASA NTRS1982

Far-infrared observations of FU Orionis

The peculiar star FU Orionis is located in the southeast extension of Barnard 35 (B35), a bright-rimmed molecular cloud, and in the more extended, low-density region around Lambda Orionis. In connection with the present investigation, far-infrared observations of the star were undertaken in order to obtain a better estimate of the total luminosity of FU Ori and to better understand its relationship with the B35 cloud. FU Orionis was observed on 1981 January 23 with the 90 cm telescope on board the NASA Kuiper Airborne Observatory. The far-infrared results suggest that much of the radiation from the stellar source does not interact with either the 225 K circumstellar dust or the exterior 15 K material. The total luminosity of FU Ori is now seen to be about the same as the visible luminosity, and at the distance to B35 ridge dilution would make any isotropic effects negligible.

Smith, H. A.↗
NASA NTRS1981

Far-infrared and submillimeter observations of Barnard 35 - Heat sources for bright-rimmed molecular clouds

Far-infrared and submillimeter continuum observations of a region of enhanced gas temperature in Barnard 35 are presented which were obtained in a study of dust and gas energetics in the bright-rimmed molecular cloud. Observations were obtained with the 90-cm telescope on board the NASA Kuiper Airborne Observatory, together with ground-based observations of the CO lines. The spectrum is found to correspond to a dust temperature of 10 + or - 5 K. A total dust luminosity of about 69 solar luminosities is estimated for the cloud, which may easily be supplied by stellar radiation from the background field or the Lambda Ori cluster. Observations of CO emission at 2.7 mm indicate a gas temperature of 23.4 + or - 3.5 K. The difference between the gas and dust temperatures confirms earlier suggestions that the gas and dust are not in thermal equilibrium and that gas-dust collisions are not the heat source for the molecular gas, however the actual source of the molecular gas heating remains uncertain.

Lada, C. J.↗
NASA NTRS1981

Far-infrared observations of the H2O masers in NGC 281, NGC 2175, and S255/257

The H2O masers in NGC 281, NGC 2175, and S255/257 have been observed in four far-infrared bands from 40-140 microns with 30 arcsec and 50 arcsec beams. The far-IR positions are consistent with the H2O positions. The far-IR sources have luminosities of 10 to the 4 + or 0.5 solar luminosities, dust temperatures of 36-50 K, H densities greater than 10 to the 4.5, and apparent masses of 12-120 solar masses.

Wright, E. L.↗
NASA NTRS1981

Low thermal conductance rigidizer for reducing torsional oscillations in cryogenic Dewars

A rigidizer, which provides greater rigidity against torsional oscillations, is highly resistant to radial motions, and has low thermal conductivity, has been developed to decrease vibrational levels affecting infrared detectors operated in cryostats (e.g., HD-3L Dewar) in aircraft such as NASA's Kuiper Airborne Observatory. The rigidizer is composed of two triangular elements and an intermediate support structure which joins them at the centers of their sides. The reentrant design provides a long heat path, while the triangular truss structure provides high rigidity in the horizontal plane. The structure is relatively compliant in the vertical direction, a desirable feature since the internal structure of the Dewar contracts as it cools. Rigidity in the vertical direction is provided by the neck tube. The support structure is quite compact. Several variants of the rigidizer have been fabricated, using flat sheets of G-10 fiberglass epoxy in thicknesses between 0.75-1.5 mm for the upper and lower truss assemblies, and either G-10 or stainless steel for the intermediate structure.

Harper, D. A.↗
NASA NTRS1980

High angular resolution far-infrared observations of the W3 region

A 2 x 3 arcmin region surrounding the W3 cluster of near-infrared sources and compact H II regions has been mapped at 30, 50, and 100 microns with an angular resolution of about 30 arcsec. The data have been used to produce maps of the distribution of luminosity, color temperature, and opacity in the far-infrared which are used to analyze the properties and evolutionary states of the individual compact sources in the cluster and of the molecular cloud in which they are embedded. The total luminosity of the near-infrared source W3-IRS 5 is estimated on the basis of these observations to be 200,000 solar luminosities, and it is identified as a forming O star.

Werner, M. W.↗
NASA NTRS1980

Search for far-infrared emission from young supernova remnants

A search has been conducted for 80-350 micron emission from the Tycho, Kepler, and Cas A supernova remnants. The bolometric fluxes are less than 5 x 10 to the -11th, 4 x 10 to the -12th, and 9 x 10 to the -12th W/sq m, respectively, for the entire radio shell, corresponding to luminosities less than 25,000, 1100, and 1500 solar luminosities (within 2 standard deviations). The ratio of dust to gas in Cas A is at least 10 times less than the 'normal' ratio.

Wright, E. L.↗
NASA NTRS1980

Far-infrared photometry of Titan and Iapetus

Titan was observed in four broad passbands between 35 and 150 microns. The brightness temperature in this interval is roughly constant at 76 plus or minus 3 K. Integrating Titan's spectrum from 5 to 150 microns yields an effective temperature of 86 plus or minus 3 K. Both the bright and dark hemispheres of Iapetus were observed in one broadband filter with a flux-weighted mean wavelength approximately equal to 66 microns. The brightness temperatures for these two sides of Iapetus are 96 plus or minus 9 K and 114 plus or minus 10 K, respectively. The bright-side Bond albedo is calculated to be 0.61(+0.16;-0.22).

Loewenstein, R. F.↗
NASA NTRS1980

Far-infrared observations of the globule B335

Far-infrared and submillimeter continuum emission from the dark globule B335 was observed. The spectrum is that of optically thin thermal emission from dust with temperature 13-16 K. The estimated dust mass is 0.07-0.17 solar masses. The observed luminosity, 5 solar luminosities, can be supplied by the interstellar radiation field.

Keene, J.↗
NASA NTRS1980

Galaxies and far-infrared emission

The far-infrared luminosities of the central few hundred parsecs of many galaxies may exceed by more than an order of magnitude the amount expected from late-type stars. However, for the M82, NGC 253, NGC 1068 and several other galaxies studied in the present paper, the inferred mass-to-luminosity ratios are within the limits expected for stellar distributions containing early-type stars.

Telesco, C. M.↗
NASA NTRS1979

Millimetre and submillimetre measurements of the Crab Nebula

The flux from the central region of the Crab Nebula in three broad spectral passbounds with flux-weighted mean wavelengths of 300 microns, 400 microns and 1 mm has been measured. The inferred total flux densities for the entire nebula are consistent with an extrapolation of the power law spectrum found at longer wavelengths. Derivations of various flux densities are presented, and it is concluded that the luminosity of dust emission from the Crab Nebula varies between 1300 and 5000 suns as the temperature varies from 40 to 120 K, respectively.

Wright, E. L.↗