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Schwartz, P. R.

Publications and source records attributed to Schwartz, P. R..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

1300 micron continuum and C(O-18) line mapping of the giant molecular cloud cores in Orion, W49, and W51

Observations of the 1300-micron continuum emission and the C(O-18) spectral-line emission from three well-studied giant molecular cloud cores: Orion, W49, and W51 are presented. The observations were obtained at the Five College Radio Astronomy Observatory, and they provide a means to examine the consistency of these two methods to trace the column density structure of molecular clouds. A good general correlation is found between the 1300-micron continuum, which traces the column density of dust, and the C(O-18) J = 2-1 line emission, which traces the column density of molecular gas, when the effects of source temperature are taken into consideration. Moreover, nominal values for the gas and dust abundances and the dust properties reproduce the observed continuum-to-line ratios. Thus, no strong C(O-18) abundance gradients within sources has been found, and it appears that either the C(O-18) emission lines or the submillimeter dust emission may used to derive the mass column density within molecular clouds accurately.

Schloerb, F. Peter↗
NASA NTRS1985

Pedestal features in dark clouds - A search for radio emission

Radio emission associated with broad-winged CO sources in B335, L1527, L1455, and L732 was searched for. No detections were made in three of the sources, B335, L1527, and L732. A nonthermal double radio source was found near the focus of the L1455 flow. This source is probably associated with the flow, and may represent a new aspect of the molecular flow phenomenon.

Schwartz, P. R.↗
NASA NTRS1985

Possible seasonal variability of mesospheric water vapor

Ground-based spectral line measurements of the 22.2 GHz water vapor line in atmospheric emission were made at the Jet Propulsion Laboratory, which have been used to deduce the mesospheric water vapor profile. The measurements were made nearly continuously in the spring and early summer of 1984. The results indicate a temporal increase in the water vapor mixing ratio in the upper mesosphere from April through June. At 75 km, this increase is nearly by a factor of 2. Comparison of the present results with the results of a similar series of measurements made at the Haystack (radio astronomy) Observatory indicate that this temporal increase is part of a seasonal variation.

Bevilacqua, R. M.↗
NASA NTRS1985

Active star formation in NGC 2264

The region of NGC 2264 near the cone nebula is the site of active star formation in a rotating ring seen nearly edge on as a two lobed source. Allen's infrared source (IRS 1) surrounds a B3V star still embedded in the southern lobe of the cloud. The northern lobe, IRS 2, also probably contains young stars.

Schwartz, P. R.↗
NASA NTRS1985

Seasonal variability of mesospheric water vapor

Ground-based spectral line measurements of the 22.2 GHz atmospheric water vapor line in emission were made at the JPL in order to obtain data in a dry climate, and to confirm similar measurements made at the Haystack Observatory. The results obtained from March 1984 to July 1984 and from December 1984 to May 1985, were based on data recorded by a HP9816 microcomputer. The instrument spectrometer was a 64 channel, 62.5 kHz resolution filter bank. Data indicates the existence of a seasonal variation in the abundance of water vapor in the upper mesosphere, with mixing ratios higher in summer than in spring. This is consistent with recent theoretical and observational results. In the area of semiannual oscillation, Haystack data are more consistent than those of JPL, indicating an annual cycle with abundances at maximum in summer and minimum in winter.

Schwartz, P. R.↗
NASA NTRS1984

Multi-spectral Observations of the Star Formation: the Role of Far Infrared Photometry

The study and analysis of complex astrophysical process requires a multispectral approach employing many of the tools of modern astronomy. The study of the interaction of early type stars with the interstellar medium is an example of this point. Two examples of multi-spectral studies of individual objects are reviewed. The predominent theme is the combination of high resolution far infrared photometry, radio images and millimeter-wave spectroscopy with the radio sensitive to the ionization, the millimeter-wave lines showing the structure and excitation of the gas and the far infrared providing a picture of the energetics of the dust which connects the star to the interstellar medium. Multispectral observations of FIRSSE and IRAS objects are discussed.

Schwartz, P. R.↗
NASA NTRS1984

The Orion Molecular Cloud at Far-infrared Wavelengths

A new, 34 in resolution far-infrared continuum map of Orion Molecular Cloud 1 and its environs, including M43 is presented. The source is dominated by a single, bright peak at the position of the embedded infrared cluster, with the 60 micro m flux density falling off steeply in all directions away from it. A total luminosity for IRc2 of 20,000 L(solar) is estimated, although this may be a lower limit, depending upon the transfer of radiation in the vicinity of the object. Several condensations appear in this map, which, along with radio molecular observations, support the view that significant fragmentation has taken place within the cloud.

Thronson, H. A., Jr.↗
NASA NTRS1984

NGC 2024: Multi-wavelength Infrared and Radio Observations

A series of far-infrared maps obtained on the KAO find the total IR luminosity of NGC 2024 is to the 4th power L, and show a peak in flux density and optical depth about 1' south of IRS 2. High resolution spectra of IRS 2 in Brackett alfa and Pfund gamma indicate the presence of an optically thick wind with M approx. 7 x 10 to the minus 7 power M sub yr to minus 1 power, from which we infer that IRS 2 is unable to supply the luminosity observed. A six centimeter continuum map peaks near the location of the far-infrared peak and confirms it as a likely site for a source to provide this luminosity. Maps in HCN, CS, and H2CO show the gas is dense in the direction of the far IR peak. Velocity analysis shows the H2 region created by the far IR source and IRS 2 forms an expanding bubble in front of which the H2CO is seen in absorption, and which is bounded in the south and behind by dense material.

Smith, H. A.↗
NASA NTRS1984

The nature of AFGL 2591 and its associated molecular outflow Infrared and millimeter-wave observations

The results of infrared photometry from 2 to 160 microns of AFGL and CO(12) observations of its associated molecular cloud and high velocity molecular outflow are presented and discussed. The observed solar luminosity is 6.7 x 10(4) at a distance of 2 kpc. The spectrum of AFGL 2591 is interpreted in the context of a model in which a single embedded object is the dominant source of the infrared luminosity. This object is determined to be surrounded by a compact, optically thick dust shell with a temperature in excess of several hundred degrees kelvin. The extinction to this source is estimated to be between 26 and 50 visual magnitudes. The absolute position of the infrared sources at 10 microns was determined to an accuracy of + or - 1 in. This indicates for the first time that the IR source and H2O source are not coincident. The CO(12) observations show the high-velocity molecular flow near AFGL 2591 to be extended, bipolar and roughly centered on the infrared emission. The observations suggest that the red-shifted flow component extends beyond the boundary of the ambient cloud within which AFGL 2591 is embedded. The CO(12) observations also show that AFGL 2591 is embedded in a molecular cloud with an LSR velocity of -5 km/s.

Lada, C. J.↗
NASA NTRS1984

W3 North - Far-infrared and radio molecular observations

The results of far-infrared and radio molecular CO observations of the W3 North star-forming region are reported. The object shows extended dust and gas emission, which is interpreted as the result of fairly advanced disruption of a molecular cloud. This idea is supported by an estimate for the age of the embedded H II region. It is possible that W3 North is the oldest object among the W3 complex of sources.

Thronson, H. A., Jr.↗
NASA NTRS1984

VLA observations of T Tauri stars. II - A luminosity-limited survey of Taurus-Auriga

The results of a 4.885-GHz VLA survey of 46 T Tau stars and Herbig-Haro objects with log L 0.2 or greater in the Taurus-Auriga dark clouds, performed in February 1982, with 40-60-min observation times, are presented in tables and contour maps and discussed. Upper limits are given for objects not detected at 4.885 GHz; additional observations at 1.465, 14.965, and 22.485 GHz are included for the objects detected; and spectral indices are derived for 10 objects. The individual objects are characterized in detail, and it is concluded that detectable radio emission is more likely for T Tau stars with associated Herbig-Haro objects than for those without. The implications of the nonthermal spectra identified in several objects for theories of theoretical models of radio emission are indicated.

Bieging, J. H.↗
NASA NTRS1984

NGC 2024: Far-infrared and radio molecular observations

Far infrared continuum and millimeter wave molecular observations are presented for the infrared and radio source NGC 2024. The measurements are obtained at relatively high angular resolution, enabling a description of 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. Maps of the source using the high density molecules CS and HCN confirm this picture and allow a description of 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' south of the bright mid infrared source IRS 2. The data presented here allows a presentation of a model for the source.

Thronson, H. A., Jr.↗
NASA NTRS1984

The nature of AFGL 2591 and its associated molecular outflow: Infrared and millimeter-wave observations

The results of infrared photometry from 2 to 160 microns of AFGL and CO(12) observations of its associated molecular cloud and high velocity molecular outflow are presented and discussed. The observed solar luminosity is 6.7 x 10(4) at a distance of 2 kpc. The spectrum of AFGL 2591 is interpreted in the context of a model in which a single embedded object is the dominant source of the infrared luminosity. This object is determined to be surrounded by a compact, optically thick dust shell with a temperature in excess of several hundred degrees kelvin. The extinction to this source is estimated to be between 26 and 50 visual magnitudes. The absolute position of the infrared sources at 10 microns was determined to an accuracy of + or in. This indicates for the first time that the IR source and H2O source are not coincident. The CO(12) observations show the high-velocity molecular flow near AFGL 2591 to be extended, bipolar and roughly centered on the infrared emission. The observations suggest that the red-shifted flow component extends beyond the boundary of the ambient cloud within which AFGL 2591 is embedded. The CO(12) observations also show that AFGL 2591 is embedded in a molecular cloud with an LSR velocity of -5 km/s.

Lada, C. J.↗
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 NTRS1982

VLA observations of mass loss from T Tauri stars

Six of 24 pre-main sequence stars surveyed with the VLA have been found to emit at 4.885 GHz. Radio maps of the six stars, V410 Tau, T Tau, DG Tau, LkH-alpha 101, L1551 IRS5, and Z CMa, show unresolved cores of less than 0.5 arcsec in most cases, along with 1-2 arcsec, faint, extended structures. Mass loss rates, derived under the assumption of uniform spherical winds, range from approximately 3 x 10 to the -7th to about 4 x 10 to the -5th solar masses/year. Because the flows are highly anisotropic, however, these estimates are to be taken only as likely upper limits.

Cohen, M.↗
NASA NTRS1981

Diurnal variations of mesospheric ozone using millimeter-wave measurements

In March 1979, millimeter-wave observations of the ozone emission line at 101737 MHz were made to measure the diurnal variations in mesospheric ozone. Changes in mesospheric ozone were measured diurnally for a 10-day period. The ozone column above approximately 76 km rapidly decreased after sunrise to half value within 1 hour and was then followed by a slower (approximately 8 hours) decrease to an absolute minimum at 1600 hours. At sunset, the ozone column above approximately 76 km increased rapidly to its maximum value within 2 hours. In the 48-68 km altitude range, the ozone changes were gradual with a minimum near local noon (1200 hours).

Wilson, W. J.↗