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Elias, J. H.

Publications and source records attributed to Elias, J. H..

29 records · Page 2
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NASA NTRS1978

An infrared study of the Ophiuchus dark cloud

A near-infrared survey has been conducted of nearly 18 square degrees of the Ophiuchus dark cloud complex. Additional observations have been made of selected objects found in this survey and of the brighter objects found by Grasdalen et al. and by Vrba et al. in this region in order to identify and study the young stars associated with the cloud. These observations show that very recent star formation has been largely restricted to a small region at the center of the dark cloud complex, no more than a few parsecs in extent. Most of the young stars do not appear to be main-sequence stars. At least three of these objects appear to be surrounded by infrared reflection nebulae. Many of the objects studied are background K and M giants which can be used to determine the near-infrared extinction due to the cloud.

Elias, J. H.↗
NASA NTRS1978

A study of the IC 5146 dark cloud complex

The IC 5146 dark cloud complex has been studied in the infrared in order to identify and study associated young stellar objects. Most of the objects detected in the survey appear to be field stars, predominantly late-type giants. Three young objects were detected in the survey: the B0 star BD +46 deg 3474, the Ae star BD +46 deg 3471, and a previously unidentified object which appears to be a heavily obscured FU Orionis star. The properties of the last two objects are examined in detail, and an attempt is made to produce reasonable models for them. It is suggested that FU Orionis stars are binaries, and some consequences of this model are described. Photometry of the brighter stars in the IC 5146 cluster has been used to establish a distance to the cluster of 900 + or - 100 pc.

Elias, J. H.↗
NASA NTRS1978

2.2-micron field stars at the North Galactic Pole

The properties of the 2.2-micron field stars seen near the North Galactic Pole by the Two Micron Sky Survey and by surveys at higher sensitivity are discussed. All the 2.2-micron sources found in these surveys can be identified with stars with known spectral types. The distribution of the 2.2-micron field stars appears to be well-understood.

Elias, J. H.↗
NASA NTRS1978

1 millimeter continuum observations of extragalactic objects

Continuum observations of 23 extragalactic objects have been made at a wavelength of 1 mm; nine of the 23 have been definitely detected at this wavelength. The sources detected include seven from which the 1-mm emission appears to be nonthermal, and two from which the emission appears to be thermal radiation from dust. Repeated observations of the brightest nonthermal sources permitted a search for 1-mm variations on time scales of one month to three years. BL Lac was observed to vary by more than a factor of 2 in flux, and 3C 84, 3C 120, and 3C 273 showed possible variations; 3C 279 showed no variations greater than + or - 30%. The 1-mm variations of BL Lac appear to be correlated with variations at radio wavelengths. The other sources with nonthermal spectra detected were 3C 111 and M87; the two thermal sources detected were NGC 253 and M82. Comparison of the latter two 1-mm measurements with 2.6-mm CO measurements suggests that the CO line in these galaxies is not heavily saturated.

Elias, J. H.↗
NASA NTRS1976

One-millimeter continuum emission studies of four molecular clouds

Maps with 1-arcmin resolution are presented of 1-mm thermal emission from dust grains in the central portions of the molecular clouds associated with four H II regions: W3, M42 (OMC-1), Sgr B2, and W49. The maps cover regions approximately 5 by 5 arcmin in extent. In each source, a sharp peak in the 1-mm surface brightness is seen at the position of a compact H II region and/or one or several luminous near-infrared sources. The radial density distributions in the center of the clouds have been estimated from the observed distribution of 1-mm surface brightness near the peaks. The results indicate that the central density gradients are quite steep. These gradients may have been established in the clouds by the collapse processes which led to the formation of the central luminous objects.

Westbrook, W. E.↗
NASA NTRS1976

Far-infrared observations of IRC + 10216

Broadband photometric observations of IRC + 10216 in five wavelength intervals from 50 to 1000 microns are reported. The observed radiation is interpreted as thermal emission from dust in the extended molecular cloud heated by the compact 2-20-micron source at the cloud core. The shape of the 50-1000-micron spectrum suggests that the emissivity of the dust particles varies approximately as the inverse wavelength over this spectral interval. The mass of dust inferred from the far-infrared emission is comparable with the mass of heavy molecules in the cloud.

Campbell, M. P.↗
NASA NTRS1975

Observations of 1-millimeter continuum radiation from the DR 21 region

Continuum emission at 1 mm has been mapped with 1-min resolution over a 3-min by 8-min area including the compact H II region DR 21, the maser source W75(S)-OH, and the central portions of the surrounding molecular cloud. Peaks in the 1-mm intensity are observed at the positions of DR 21 and W75(S)-OH, and are roughly coincident with less marked peaks in the intensity of HCN and CO emission. An extended component of 1-mm emission is present as well. The principal source of 1-mm radiation is thought to be thermal emission from dust within the molecular gas. The characteristics of this radiation which make it a promising tool for the study of molecular clouds are briefly discussed.

Werner, M. W.↗
NASA NTRS1974

1-millimeter continuum radiation from Orion Molecular Cloud 2

The 1-mm continuum flux from Orion Molecular Cloud 2 (OMC-2), measured with a 1-inch beam, is found to be 0.05 plus or minus 0.01 of that from the Becklin-Neugebauer/Kleinmann-Low (BN/KL) complex. This implies that the average density of dust within OMC-2 is about an order of magnitude less than within the BN/KL region.

Werner, M. W.↗