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Thronson, H. A., Jr.

Publications and source records attributed to Thronson, H. A., Jr..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The Bubble Nebula - Far-infrared and radio molecular observations of NGC 7635

The Bubble Nebula, NGC 7635, has been partially mapped at 1 arcmin resolution in the far-infrared and completely mapped at 2.2 arcmin resolution in 115-GHz emission from CO. The infrared results are consistent with the presence of only a small amount of dust within the optical part of the nebula, in agreement with previous work at visual wavelengths. The dust may be fairly uniformly spread through the H II region, although some variation in density is necessary to explain the observed temperature distribution of the dust. The CO emission is weak and the CO column density is very low, consistent with the low obscuration observed in the region. Nevertheless it is surprising that any molecules can exist in the neighbourhood of the luminous exciting star of NGC 7635 and a special geometrical configuration may be necessary.

Thronson, H. A., Jr.↗
NASA NTRS1982

Far-infrared sources in Cygnus X - An extended emission complex at DR 21 and unresolved sources at S106 and ON 2

A new map of 90 micron emission with 15 arcmin resolution is presented of a complex of sources approximately centered on DR 21. The emission is primarily from diffuse sources. Comparison of the 90 micron map with maps at 20 microns and 2.7 GHz leads to a model for diffuse sources in which there are at least two components of interstellar dust, one at 40 K and one at 165 K, responsible for the 90 micron and 20 micron emission respectively. Both components and the ionized gas must be mixed together; dust in an outer neutral shell is relatively unimportant for these sources. The diffuse sources have small infrared excesses and weak temperature gradients. Unresolved, probably compact, sources were observed at S106 and ON 2 and are briefly discussed.

Campbell, M. F.↗
NASA NTRS1982

Far-infrared mapping of the double-lobed H II region S106

Photometry of S106 at 50 and 100 microns, as well as its mapping with 35 arcsec resolution and a search for a nearby H2O maser source at 2 and 10 microns, have yielded data that are consistent with a 900 pc distance and an O9 (ZAMS) spectral type for a single, central exciting star. The correlation of dust temperature with optical emission, and anticorrelation of dust optical depth with optical emission, support models of S106 which envision an exciting star surrounded by a dusty disk having very low optical extinction along its approximately north-south axis. A local maximum in the dust column density was found to the west of the optical nebula, near the position of an H2O maser, although no local near- or far-IR flux maximum was detected.

Harvey, P. M.↗
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

An extended far-infrared emission complex at IC 1318b and IC 1318c

A map of extended 90 micron emission with 15 arcmin resolution is presented for sources centered on IC 1318b and c. A strong correlation is found between far-infrared emission and radio continuum emission, although a comparison of far-infrared and CO molecular line maps shows no similarity. Extended far-infrared sources have inferred gas densities, which implies that far-infrared emitting dust is mixed with the ionized gas. Far-infrared emission from dust is also observed in the nonthermal radio source DR 4 which is part of a supernova remnant, and the data are compatible with a core-halo model for the compact source DR 7.

Campbell, M. F.↗
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

Star formation in IC 1848 A

Recent far-infrared photometric and near-infrared spectroscopic observations of IC 1848 A/W5 East are reported. The source appears to be excited by a star of spectral type near B0, which can explain the far-infrared luminosity, 2 micron spectrum, radio continuum, and radio molecular observations. Although this star appears surrounded by a local very compact H II region, the density over a large scale is relatively low. This puts constraints on models for the formation of this star.

Thronson, H. A., Jr.↗
NASA NTRS1980

The large-scale far-infrared structure of W3 and W4

The large-scale structure of the giant H II region complex W3/W4 has been mapped in two wavelength bands covering 60 to 120 microns at an angular resolution of 12 arc min. The only region of strong emission observed lies along a molecular ridge at an ionization/shock front in the sources. This structure supports the idea that a new generation of stars formed after neutral material ahead of the front became gravitationally unstable. These embedded stars are dominating the energetics of the molecular/infrared cloud, although the visible OCl 352 cluster in neighboring IC 1805 may supply much of the heating flux to the fainter regions. A simple model relating the far-infrared and CO emission is presented.

Thronson, H. A., Jr.↗
NASA NTRS1980

Far-infrared survey of Cygnus X

Results of a new far-infrared survey of Cygnus X conducted with 12-arcmin resolution are presented. Forty-nine sources were observed, 39 of them for the first time. Associations are made with sources from mid-infrared, radio continuum, and CO radio line surveys.

Campbell, M. F.↗
NASA NTRS1980

A far-infrared study of the reflection nebula NGC 2023

Multicolor mapping of the reflection nebula NGC 2023 from 40 to 160 microns is presented. These data show the shorter wavelength emission to peak on or close to the exciting star HD 37903. The longest wavelength emission, however, peaks about 1 arcmin south of HD 37903, at a position coincident with the C II recombination line peak. The dust temperature appears to peak close to HD 37903 suggesting that it is probably the most luminous heating source for the cloud. The far-infrared data together with 10 microns photometry of HD 37903 imply a roughly uniform dust mass density within 0.1 pc of the star with no significant density increase toward the star. The results imply that the gas and dust column density increase slightly to the south of HD 37903 and that the bulk of the molecular cloud lies behind the star and the reflection nebula.

Harvey, P. M.↗
NASA NTRS1979

Far-infrared observations of the Lagoon Nebula /M8/

Large-beam far-infrared photometry is used to estimate the dust temperature and mass, geometry, and energetics of the Lagoon Nebula (M8). Most of the data can be explained in terms of the visible star cluster, NGC 6530, heating a dense molecular cloud that lies behind it. The source M8E, however, may be heated internally, and appears to be a likely site of very recent star formation. The associated molecular cloud may be the location of future stellar formation activity as well.

Thronson, H. A., Jr.↗
NASA NTRS1979

Far-infrared observations of optical emission-line stars - Evidence for extensive cool dust clouds

Far-infrared observations (40-160 microns) of eight optical emission-line stars are presented. Six of these stars, LkH-alpha 198, T Tau, LkH-alpha 101, V380 Ori, R Mon, and MWC 1080, show substantially more far-infrared emission than would be expected on the basis of a blackbody extrapolation of their 10-20-micron fluxes. Additionally, in three cases, the far-infrared emission is shown to be spatially extended (greater than 40 arcsec). A simple model of the thermal emission from cool circumstellar dust (30-70 K) shows that these stars are surrounded by material left over from the star formation process; this result confirms the extreme youth of these stars. MWC 349 was detected at a level consistent with the expected free-free flux from its surrounding H II region, and RY Tau was not detected in the far-infrared; there is little circumstellar dust with temperatures of 20-100 K in these objects.

Harvey, P. M.↗
NASA NTRS1979

Compact H II regions in the far-infrared

Far-infrared (40-150 microns) observations of W51 (G49.5-0.4), K3-50, DR 21, NGC 7538, and W3(OH) are presented and discussed. At these wavelengths each source is dominated by a small bright component closely associated with a compact H II region. Their spectra can be explained as emission by dust at temperatures of 30-50 K. Some of the objects appear to be optically thick out to wavelengths of about 60 microns. Of the 10 source components in the five regions, at least four may be powered by pre-main-sequence stars. The far-infrared data are consistent with depletion of volatile components of the dust within compact H II regions, but do not clearly require destruction or expulsion of refractory grains. The bulk of the dust which emits primarily in the far-infrared must lie in a dense shell immediately outside the ionized zone. The sources are possible precursers to open clusters with stellar masses in the range from 1,000 to 10,000 solar masses.

Thronson, H. A., Jr.↗
NASA NTRS1979

Infrared observations of NGC 2071/IRS/ and AFGL 490 - Two low-luminosity young stars

Infrared observations are presented of two compact sources associated with molecular clouds. Photometry from 2 to 200 microns of the source associated with an OH maser in NGC 2071, OH 205.1-14.1, shows a steep increase in flux from 2 to 50 microns. Scans at several wavelengths fail to resolve the source. Photometry at 50-200 microns of the other object, GL 490, when combined with earlier 2-20-micron spectrophotometry, shows an infrared energy distribution that is much broader than that of the NGC 2071 source. Both sources are interpreted as young, possibly pre-main-sequence objects with differences in energy distributions due principally to differences in the distribution of circumstellar matter.

Harvey, P. M.↗
NASA NTRS1979

Star formation at a front - Far-infrared observations of AFGL 333

Far-infrared maps of AFGL 333 at 50 and 100 microns with 40 arsec resolution are presented. The observed luminosity of about 14,000 suns, together with previous radio continuum observations, indicates that the source is powered by a B0.5 zero-age main-sequence star. The relatively low molecular density of about 1000 per cu cm inferred from the observed dust optical depth probably implies that AFGL 333 is not as young as the other H II/infrared objects, W3(A) and W3(OH), in the W3/W4 system.

Thronson, H. A., Jr.↗
NASA NTRS1979

An upper limit to far infrared emission from the Crab nebula

Upper limits to the 50- and 100-micron emission from the Crab nebula are reported. These data are consistent with a spectrum that follows a power-law interpolation between the millimeter and near-infrared fluxes. The data are interpreted in terms of an upper limit to thermal emission by dust in the nebula. The upper limit to the amount of dust present is consistent with previously reported upper limits to optical extinction associated with the nebula.

Harvey, P. M.↗