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Lada, C. J.

Publications and source records attributed to Lada, C. J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The bipolar molecular outflow of V645 Cygni

A map is presented of the CO J = 3-2 line emission from the cloud associated with V645 Cygni. Line wings extending to 15 km/s on either side of the central velocity can be attributed to a bipolar outflow over a region 1 arcmin in angular extent. The redshifted and blueshifted emission peaks are separated by 20 arcsecs along an axis that is approximately perpendicular to the polarization vector of the visible light. The outflow is of relatively low velocity, low mass, and low mechanical luminosity.

Schulz, A.↗
NASA NTRS1985

The W3 molecular cloud

Extensive J = 1 to 0 (C-12)(O-16) and (C-13)(O-16) observations of the W3 molecular cloud and the surrounding region are presented and discussed. The velocity structure in the region is strongly suggestive of a model of large-scale, externally induced star formation. It is shown that star formation occurred in W3 and the nearby star-forming region W3(OH) after the gas within which they lie was swept up by the expanding W4 ionization front. Two condensations dominate the mass structure of the core of W3, one associated with IRS 4 and the other with IRS 5 and 1. A velocity difference between the two condensations is interpreted as indicating the two sources actually are discrete knots.

Thronson, H. A., Jr.↗
NASA NTRS1984

The nature of the embedded population in the Rho Ophiuchi dark cloud - Mid-infrared observations

In combination with previous IR and optical data, the present 10-20 micron observations of previously identified members of the embedded population of the Rho Ophiuchi dark cloud allow determinations to be made of the broadband energy distributions for 32 of the 44 sources. The majority of the sources are found to emit the bulk of their luminosity in the 1-20 micron range, and to be surrounded by dust shells. Because they are, in light of these characteristics, probably premain-sequence in nature, relatively accurate bolometric luminosities for these objects can be obtained through integration of their energy distributions. It is found that 44 percent of the sources are less luminous than the sun, and are among the lowest luminosity premain-sequence/protostellar objects observed to date.

Lada, C. J.↗
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

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

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 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

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 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 NTRS1984

The formation of massive stars along the W5 ionization front

Far-infrared, near-infrared, millimeter-wave, and optical data are presented for two of the large molecular clouds which border the W5 (IC 1848) giant H II region. These data are combined to identify three B0-B2 zero-age main-sequence stars which are forming in these clouds and to study the density distribution and kinematic structure of their surrounding molecular gas. This investigation into the environment in which massive stars have formed in these clouds, when considered alongside similar studies of the W5A/S201 molecular cloud, leads to the conclusion that the expanding W5 H II region has played an important role in initiating the formation of these massive stars.

Wilking, B. A.↗
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 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

The energetic molecular outflow near AFGL 961 - Millimeter-wave and infrared observations

Sensitive millimeter-wave C-12O line observations and near-infrared hydrogen recombination line observations of AFGL 961 are reported and analyzed. The observations show that the high-velocity flow has a maximum extent of at least six arcmin or 1.9 pc at the distance of AFGL 961. The flow is anisotropic and the emission profiles are asymmetric in velocity. The mass of the gas involved in the flow is determined to be approximately 19 solar masses, and the kinetic energy of this gas is estimated to be about 8 x 10 to the 46th ergs. These observations are interpreted as evidence that an energetic bipolar outflow of molecular gas is occurring near AFGL 961. Comparison of infrared recombination line data, radio continuum, and CO observations shows that a strong, ionized, stellar wind would not be a sufficient force to drive the outflow. The effects of the outflow on the surrounding molecular cloud was also investigated.

Lada, C. J.↗