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Goldsmith, Paul F.

Publications and source records attributed to Goldsmith, Paul F..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

The Herschel Oxygen Project: Herschel Space Observatory Open Time Key Project

Topics include: Why oxygen and why at submillimeter wavelengths; gas phase chemistry for water, oxygen, and carbon monoxide is relatively simple; molecular oxygen structure; lower rotational levels and transitions of oxygen; oxygen abundance in interstellar clouds; SWAS spectra of terrestrial oxygen; what Herschel offers HOP; key regions for probing oxygen in the dense interstellar medium; HOP sources and strategy; and HOP data and analysis.

astrochemistry↗
NASA NTRS2008

Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Spatial Dynamic Range Spectral Line Mapping

Viewgraph topics include: optical image of Taurus; dust extinction in IR has provided a new tool for probing cloud morphology; observations of the gas can contribute critical information on gas temperature, gas column density and distribution, mass, and kinematics; the Taurus molecular cloud complex; average spectra in each mask region; mas 2 data; dealing with mask 1 data; behavior of mask 1 pixels; distribution of CO column densities; conversion to H2 column density; variable CO/H2 ratio with values much less than 10(exp -4) at low N indicated by UV results; histogram of N(H2) distribution; H2 column density distribution in Taurus; cumulative distribution of mass and area; lower CO fractional abundance in mask 0 and 1 regions greatly increases mass determined in the analysis; masses determined with variable X(CO) and including diffuse regions agrees well with the found from L(CO); distribution of young stars as a function of molecular column density; star formation efficiency; star formation rate and gas depletion; and enlarged images of some of the regions with numerous young stars. Additional slides examine the origin of the Taurus molecular cloud, evolution from HI gas, kinematics as a clue to its origin, and its relationship to star formation.

molecular clouds↗
NASA NTRS2006

Cold Atomic Hydrogen, Narrow Self-Absorption, and the Age of Molecular Clouds

This viewgraph presentation reviews the history, and current work on HI and its importance in star formation. Through many observations of HI Narrow Self Absorption (HINSA) the conclusions are drawn and presented. Local molecular clouds have HI well-mixed with molecular constituents This HI is cold, quiescent, and must be well-shielded from the UV radiation field The density and fractional abundance (wrt H2) of the cold HI are close to steady state values The time required to convert these starless clouds from purely HI initial state to observed present composition is a few to ten million years This timescale is a lower limit - if dense clouds being swept up from lower density regions by shocks, the time to accumulate material to get A(sub v) is approximately 1 and provide required shielding may be comparable or longer

star formation↗
NASA NTRS2006

Massive Quiescent Cores in Orion - The Core Mass Function

CMF studies to date have been largely restricted to low-mass star-forming regions. The present study focuses on a HIGH MASS star forming region, ORION, but observes positions sufficiently far from KL that effects of previously-formed massive stars are not overwhelming

molecular cloud cores↗
NASA NTRS2000

First Detection of Methanol in a Class O Protostellar Disk

We report the detection of emission from methanol in a compact source coincident with the position of the L1157 infrared source, which we attribute to molecules in the disk surrounding this young, Class O protostellar object. In addition, we identify a spectral feature in the outflow corresponding to an ethanol transition. Using the Caltech Owens Valley Millimeter Array with a synthesized beam size of 2", we detect spatially unresolved methanol in the 2(sub k) - 1(sub k) transitions at 3mm, which is coincident in position with the peak of the continuum emission. The gas phase methanol could be located in the central region (< 100 AU radius) of a flat disk, or in an extended heated surface layer (approx. 200 AU radius) of a flared disk. The fractional abundance of methanol X(CH3OH) is approx. 2 x l0(exp -8) in the flat disk model, and 3 x l0(exp -7) for the flared disk. The fractional abundance is small in the disk as a whole, but considerably larger in the warm portions. This difference indicates that substantial chemical processing probably takes place in the disk via depletion and desorption. The methanol desorbed from the grains in the warm surface layers returns to the icy grain mantles in the cooler interior of the disk, where it is available to become part of the composition of solar system-like bodies, such as comets, formed in the outer circumstellar region. This first millimeter-wavelength detection of a complex organic molecule in a young protostellar disk has implications for disk structure and chemical evolution and for potential use as a temperature probe. The research of TV and WL was conducted at the Jet Propulsion Laboratory, California Institute of Technology with support from the National Aeronautics and Space Administration.

Velusamy, T.↗
NASA NTRS2000

Implications of SWAS Observations for Interstellar Chemistry and Star Formation

A long standing prediction of steady state gas-phase chemical theory is that H2O and O2 are important reservoirs of elemental oxygen and major coolants of the interstellar medium. Analysis of SWAS observations has set sensitive upper limits on the abundance Of O2 and has provided H2O abundances toward a variety of star forming regions. Based on these results, we show that gaseous H2O and O2 are not dominant carriers of elemental oxygen in molecular clouds. Instead the available oxygen is presumably frozen on dust grains in the form of molecular ices, with a significant portion potentially remaining in atomic form, along with CO, in the gas phase. H2O and O2 are also not significant coolants for quiescent molecular gas. In the case of H2O, a number of known chemical processes can locally elevate its abundance in regions with enhanced temperatures, such as warm regions surrounding young stars or in hot shocked gas. Thus, water can be a locally important coolant. The new information provided by SWAS, when combined with recent results from the Infrared Space Observatory, also provide several hard observational constraints for theoretical models of the chemistry in molecular clouds and we discuss various models that satisfy these conditions.

Bergin, Edwin A.↗
NASA NTRS2000

An Analysis of Water Line Profiles in Star Formation Regions Observed by SWAS

We present spectral line profiles for the 557 GHz 1(sub 1,0) yields 1(sub 0,1) ground-state rotational transition of ortho-H2(16)O for 18 galactic star formation regions observed by SWAS. 2 Water is unambiguously detected in every source. The line profiles exhibit a wide variety of shapes, including single-peaked spectra and self-reversed profiles. We interpret these profiles using a Monte Carlo code to model the radiative transport. The observed variations in the line profiles can be explained by variations in the relative strengths of the bulk flow and small-scale turbulent motions within the clouds. Bulk flow (infall, outflow) must be present in some cloud cores, and in certain cases this bulk flow dominates the turbulent motions.

Ashby, Matthew L. N.↗
NASA NTRS1994

The giant molecular cloud Monoceros R2. 1: Shell structure

We have obtained a 45 sec resolution, Nyquist-sampled map in CO J = 1-0 covering approximately a 3 deg x 3 deg region of the giant molecular cloud Monoceros R2. The map consists of 167,000 spectra observed with the 15 element focal-plane array system on the FCRAO 14 m telescope. The data reveal that the large-scale structure of Mon R2 is dominated by a is approximately 30 pc diameter largely hemispherical shell containing approximately 4 x 10(exp 4) solar mass of molecular material and expanding at approximately 3-4 km s(exp -1) with symmetric axis roughly along the line of sight. The dynamical timescale of the shell is estimated to be approximately 4 x 10(exp 6) yr, which is consistent with the age of main-sequence stars powering the clusters of reflection nebulea in this region. There is no evidence for a redshifted shell on the far side of the interior 'bubble,' which is largely devoid of molecular material. Distortions of the shell are obvious, suggesting inhomogeneity of the cloud and possible presence of a magnetic field prior to its formation. Dense clumps in Mon R2, including the main core and the GGD 12-15 core, appear to be condensations located on the large shell. The reflection nebulea with their illuminating stars as well as embedded IRAS sources suggest that triggered star formation has taken place over a large part of the Mon R2 shell.

Xie, Taoling↗
NASA NTRS1993

Cometary globules in the southeast quadrant of the Rosette nebula

We present a study of newly identified cometary globules in the southeast quadrant of the Rosette nebula using the J = 1-0 transition of carbon monoxide. The globules are found to be blueshifted by about 6 km/s with respect to the adjacent Rosette molecular cloud. The masses of the globules vary from 50 to 300 solar masses, and their sizes are between 1 and 3 pc. Two of the globules have cometary morphology and show velocity gradients of about 1.5 km/s/pc along their symmetry axes. These globules are associated with the IRAS sources 06314+0421, X0632+043, 06322+0427, and 06327+0423 which coincide with local maxima in the (C-13)O emission. The derived physical parameters of the globules are found to be consistent with those predicted by recent theoretical models of photoevaporating cometary clouds. We suggest that star formation induced by radiation driven implosion has occurred.

Patel, Nimesh A.↗
NASA NTRS1993

Dust temperature distributions in star-forming condensations

The FIR spectra of the central IR condensations in the dense cores of molecular clouds AFGL 2591. B335, L1551, Mon R2, and Sgr B2 are reanalyzed here in terms of the distribution of dust mass as a function of temperature. FIR spectra of these objects can be characterized reasonably well by a given functional form. The general shapes of the dust temperature distributions of these objects are similar and closely resemble the theoretical computations of de Muizon and Rouan (1985) for a sample of 'hot centered' clouds with active star formation. Specifically, the model yields a 'cutoff' temperature below which essentially no dust is needed to interpret the dust emission spectra, and most of the dust mass is distributed in a broad temperature range of a few tens of degrees above the cutoff temperature. Mass, luminosity, average temperature, and column density are obtained, and it is found that the physical quantities differ considerably from source to source in a meaningful way.

Xie, Taoling↗
NASA NTRS1992

High angular resolution far-infrared observations of Sagittarius B2

High-angular-resolution FIR observations of the continuum emission from the Sagittarius B2 molecular cloud core are reported. Evidence is found for a significantly spatially extended component of the FIR emission at 50- and 100-micron wavelength, which has an angular extent of 1 x 2 arcmin. Its approximate spatial coincidence with a low-level extended component of the radio free-free emission and with the portion of the SGR B2 core having densities not less than 10 exp 5 cu cm derived from molecular observations suggests that the ionizing radiation from the massive stars in the compact sources is diffusing through a region with a beam-averaged visual extinction not less than a few hundred mag. It is inferred that the gas and the dust in the central portion of the cloud surrounding the compact radio free-free/FIR sources are highly clumped.

Goldsmith, Paul F.↗
NASA NTRS1992

Coherent systems in the terahertz frequency range: Elements, operation, and examples

The topics are presented in viewgraph form and include the following: terahertz coherent systems applications; a brief overview of selected components; radiometry and spectroscopy--astronomy; radiometry--aircraft all weather landing system; radiometry--atmospheric remote sensing; plasma diagnostics; communications; radar systems; and materials measurement and manufacturing process control.

Goldsmith, Paul F.↗
NASA NTRS1992

Zone plate lens antennas for millimeter and submillimeter wavelengths

Zone plate lenses are a type of focusing element which function essentially as differential phase shifters, having a relatively few, coarsely quantized phase delays across the incident beam of radiation. The major advantages are ease of fabrication and much reduced thickness, compared to conventional refractive focusing elements. These considerations are both of particular importance for the submillimeter range, in which manufacturing tolerances for curved optical elements can pose significant problems, and where the absorption of readily available dielectric materials is quite large. In this presentation we briefly review the theory of zone plate lens operations, present a relatively simple method for calculating the aperture efficiency of zone plate lenses used as antennas, and show some theoretical and measured results in the 100 GHz range.

Goldsmith, Paul F.↗
NASA NTRS1991

A new method for analyzing IRAS data to determine the dust temperature distribution

In attempting to analyze the four-band IRAS images of interstellar dust emission, it is found that an inversion theorem recently developed by Chen (1990) enables distribution of the dust to be determined as a function of temperature and thus the total dust column density, for each line of sight. The method and its application to a hypothetical IRAS data set created by assuming a power-law dust temperature distribution, which is characteristic of the actual IRAS data for the Monoceros R2 cloud, are reported. To use the method, the wavelength dependence of the dust emissivity is assumed and a simple function is fitted to the four intensity-wavelength data points. The method is shown to be very successful at retrieving the dust temperature distribution in this case and is expected to have wide applicability to astronomical problems of this type.

Xie, Taoling↗
NASA NTRS1989

Dust emission in the Sagittarius B2 molecular cloud core

A model is presented for the dust emission from the Sagittarius B2 molecular cloud core which reproduces the observed spectrum between 30 and 1300 micron, as well as the distribution of the emission at 1300 micron. The model is based on the assumption that Sgr B2(N) continuum source is located behind the dust cloud associated with Sgr B2(M) continuum source. The fact that Sgr B2(N) is stronger at 1300 micron can be attributed to a local column density maximum at the position of this source. Absence of a 53 micron emission peak at the position of Sgr B2(N) suggests that the luminosity of the north source is lower than that of the middle source.

Lis, Dariusz C.↗
NASA NTRS1988

Identification of RNO 43 and B335 as two highly collimated bipolar flows oriented nearly in the plane of the sky

An analysis of CO and CS line observations shows that RNO 43 and B335 are single highly collimated bipolar flows oriented nearly in the plane of the sky. The angle between the line of sight and the flow axis is estimated to be 85 deg in RNO 43 and 82 deg in B335. The results indicate that each of these flows must have a significant expansion velocity perpendicular to its axis, and that the flow in B335 must be driven by a mostly nonmolecular wind component.

Cabrit, Sylvie↗
NASA NTRS1986

Variations in the HCN/HNC abundance ratio in the Orion molecular cloud

Observations of the rare isotopes of HCN and HNC have been used to determine the relative abundance of these two chemical isomers along the central ridge of the Orion molecular cloud. The abundance ratio HCN/HNC decreases by more than an order of magnitude from the relatively warm plateau and hot core sources toward the KL nebula to the colder, more quiescent clouds to the north and south. Even in the cooler regions, however, the ratio is an order of magnitude larger than that found in previous investigations of cold dark clouds. The kinetic temperature in the regions studied is determined from new observations of methylacetylene (CH3CCH), together with other recent estimates of the gas temperature near KL. The results suggest that the warmer portions of the cloud are dominated by different chemical pathways that those in the general instellar cloud material.

Goldsmith, Paul F.↗