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NASA NTRS1991

New low-resolution spectrometer spectra for IRAS sources

Low-resolution spectra of 486 IRAS point sources with F sub nu(12 microns) in the range 20-40 Jy are presented. This is part of an effort to extract and classify spectra that were not included in the Atlas of Low-Resolution Spectra and represents an extension of the earlier work by Volk and Cohen which covers sources with F sub nu(12 microns) greater than 40 Jy. The spectra have been examined by eye and classified into nine groups based on the spectral morphology. This new classification scheme is compared with the mechanical classification of the Atlas, and the differences are noted. Oxygen-rich stars of the asymptotic giant branch make up 33 percent of the sample. Solid state features dominate the spectra of most sources. It is found that the nature of the sources as implied by the present spectral classification is consistent with the classifications based on broad-band colors of the sources.

Volk, Kevin↗

NASA NTRS1992

IRAS observations of novae. III - The related objects

Results are presented on an analysis of IRAS observations of a selected sample of 116 objects that show properties similar to those of classical novae detected and modeled by Harrison and Gehrz (1988, 1991). These objects include dwarf novae, novalike variables, symbiotic stars, and planetary nebulae with close binary central-star systems. A high detection rate of 80 percent was found for this sample, as compared with about 50 percent detection rate found in the earlier examined sample. A reexamination of data showed that, at low galactic latitudes, source confusion can account for many of the detections of novae. The seemingly high detection rates of other objects and the many high-latitude novae are difficult to explain.

Harrison, Tom↗

NASA NTRS1993

The large-scale morphology of IRAS galaxies

At present, visual inspection is the only method for comparing the large-scale morphologies in the distribution of galaxies to those in model universes generated by N-body simulations. To remedy the situation, we have developed a set of three structure functions (S1, S2, S3) that quantify the degree of large-scale prolateness, oblateness, and sphericity/uniformity of a 3-D particle distribution and have applied them to a volume-limited (less than = 4000 km/s) sample of 699 IRAS galaxies with f sub 60 greater than 1.2 Jy. To determine the structure functions, we randomly select 500 galaxies as origins of spherical windows of radius R sub w, locate the centroid of the galaxies in the window (assuming all galaxies have equal mass) and then, compute the principal moments of inertia (I sub 1, I sub 2, I sub 3) about the centroid. Each S sub i is a function of (I sub 2)/(I sub 1) and (I sub 3)/I sub 1). S1, S2, and S3 tend to unity for highly prolate, oblate, and uniform distributions, respectively and tend to zero otherwise. The resulting 500 values of S sub i at each scale R sub w are used to construct a histogram.

Babul, Arif↗

NASA NTRS1993

IRAS studies of galactic supershells

Using IRAS Skyflux images and a new catalog of OB stars in the Cygnus region, a complete infrared supershell surrounding the Cyg OB1 Association was identified. This supershell is seen as a conspicuous, well-defined 2 deg x 5 deg region deficient of IR emission, with a limb-brightened edge and dimensions of about 50 x 130 pc at 1.5 kpc. The shell's elongated morphology is consistent with OB-star subclustering over the approximately 10(exp 6) yr age of the bubble. With a parent star cluster still visible (10 O stars between 25 and 45 solar mass, 3 - 4 Wolf-Rayet stars, and the possibility of 3 - 5 more massive stars that died as supernovae) the Cyg OB1 supershell is an excellent object for studying the formation and evolution of Galactic supershells. A discrepancy between the less than or equal to 1 Myr bubble age estimated from its size and the 5 Myr cluster turnoff age (45 solar mass) may require non-coeval massive star formation to explain the number of post-main-sequence stars and limit the number of past supernovae.

Saken, Jon M.↗

NASA NTRS1992

IRAS observations of young stellar objects in the Corona Australis dark cloud

The young stellar object (YSO) population associated with the dark cloud complex in Corona Australis is studied by synthesizing IRAS data with newly obtained near-IR and mid-IR photometry and previously published optical/IR data. Twenty-four YSOs in the Cr A complex are identified. The observed range of spectral energy distribution shapes and bolometric luminosities are consistent with those observed in other dark clouds. The duration and efficiency of star formation are found to be similar to the Rho Ophiuchi IR cluster. The low number of YSOs compared to other dark clouds is understood by a reevaluation of the molecular mass of the R Cr A cloud which shows it to be much less massive than previously assumed.

Wilking, Bruce A.↗

NASA NTRS1992

IRAS observations and the stellar content of H II regions in the Large Magellanic Cloud

IRAS far-infrared fluxes are presented for six H II regions in the LMC. These regions are the sites of recent, massive star formation where the radiative heating source is young stars rather than the general interstellar radiation field. As such, the observations become building blocks for the interpretation of far-infrared emission from spatially unresolved galaxies. In addition, the multiwavelength luminosities of the region then probe the young stellar upper initial mass function. With the long-range goal of determining the stellar content of unresolved star-forming regions, we present the results of a simple model which combines the infrared data with existing H-alpha/H-beta and thermal radio data. For the two OB associations where the mass function has been determined directly, the model correctly 'predicts' a solar neighborhood upper mass function within the uncertainties. No evidence is found for upper mass functions significantly different from that in the solar neighborhood.

Degioia-Eastwood, Kathleen↗

NASA NTRS1992

A survey of small-scale extremes in extinction at low Galactic latitudes using IRAS galaxies

Optical CCD and 21 cm H I data are combined here via the Tully-Fisher relation to study the Galactic extinction in the V an I bands over an angular scale of a few arcmin at absolute Galactic latitudes between 2 and 16 deg. Extinctions in V and I bands are found to be linearly correlated with A(I) about 0.58 A(V), with no noticeable environmental dependence and consistent with existing results of Galactic reddening. There is a large scatter in the simple linear relation with csc /b/, confirming the existence of 'holes' and patches at low Galactic latitudes. The mean correlation between Galactic extinction and H I column density over a comparable angular scale is also found to be consistent with those at high latitudes over large angular scales. Correlation is also found between optical extinction and the IRAS 100 micron sky brightness, and this sky brightness is only slightly worse than H I column density as an indicator for optical extinction.

Lu, N. Y.↗

NASA NTRS1992

Multiple jets from the young star IRAS 21334 + 5039

The source IRAS 21334 + 5039, a young stellar object (YSO) with broad CO outflow velocity profiles, was imaged in the 1-2 micron region with broad-band J, H, and K filters, and with a Fabry-Perot set to the molecular hydorgen v = 1-0 S(1) line, the hydrogen Br-gamma recombination line, and the neighboring continua. At 2 microns the source has an elongated continuum emission structure centered on the star. The structure has very blue tips, with a weak VLA 6 cm continuum source coincident with one of them. Strong molecular hydrogen emission appears as bow-shaped arcs oriented along an axis perpendicular to the continuum emission, and as a weaker structure aligned with it. Both the continuum and the molecular hydrogen emission are most likely produced by jets, possibly emanating in multiple directions from the central source at large angles to each other. While jets are a common feature of young stars, this source provides solid evidence for multiple jet structures.

Smith, Howard A.↗

NASA NTRS1992

High spatial resolution continuum and H-alpha imaging of the high-redshift IRAS source FSC 10214+4724

New observations are reported which support the view that the high-redshift IRAS source FSC 10214+4724 is a rare extreme example of the class of ultraluminous infrared galaxies observed in the local universe. The presence of two continuum components and a compact H-alpha source suggests that a merger between two or more gas-rich systems has triggered the production of a powerful dust-enshrouded quasar which is responsible for the bulk of the luminosity.

Soifer, B. T.↗

NASA NTRS1992

Spectral irradiance calibration in the infrared. II - Alpha Tau and the recalibration of the IRAS low resolution spectrometer

A general process for creating complete, continuous, and absolutely calibrated 1-35 micron stellar spectra is described. The method is demonstrated by constructing an absolutely calibrated 1-35 micron spectrum of Alpha Tau and the method is independently validated using new observations. The absolute calibration of the IRAS low resolution spectrometer (LRS) data base is investigated by comparing the observed spectrum of Alpha Tau with that assumed in the original LRS calibration scheme. An analysis of asteroidal LRS spectra results in an independent assessment of the calibration problems with the LRS and provides a natural complement to the effort based on Alpha Tau. A direct comparison of LRS stellar spectra with independently calibrated long-wavelength airborne and ground-based spectra is made.

Cohen, Martin↗

NASA NTRS1991

Implications of the IRAS survey for Galactic gamma-ray astronomy

Using the results of the IRAS far-infrared survey of the Galaxy, we have obtained the large-scale radial distributions of Galactic far infrared emission independently for both the Northern and Southern Hemisphere sides of the Galaxy. We find the dominant feature in these distributions to be a broad peak coincident with the '5 kpc' molecular gas cloud ring. We also find evidence of spiral arm features. Strong correlations are evident between the large scale Galactic distributions of far infrared emission, gamma-ray emission and CO emission. We find a particularly tight correlation between the distribution of warm molecular clouds and far-infrared emission on a Galactic scale.

Stecker, F. W.↗

NASA NTRS1993

Magnetic field in a low-mass protostar disk - Millimeter polarimetry of IRAS 16293-2422

We have measured the millimeter polarization of IRAS 16293-2422, a low-mass protostar candidate embedded in the east streamer of the Rho Ophiuchi dark cloud. The source has a linear polarization at 1.1 mm of (2.8 +/- 0.5) percent at a position angle of 144 deg +/- 5 deg with a 19 arcsec beam. If this polarization is due to thermal emission from magnetically aligned nonspherical grains in a dust disk around the central (proto)star, then the magnetic field threads across the disk at a position angle of 54 deg +/- 5 deg projected on the sky. This direction is the same as that of the minor axis of the elongated circumstellar gas disk (of scale 1600 AU) and of the direction of one of the quadratic outflows. There is no positive evidence for a twisted magnetic field in the dust disk, which constrains the hydromagnetic models for molecular outflows, at least for this source.

Tamura, Motohide↗

NASA NTRS1993

High-resolution study of luminous infrared galaxies. I - The composite nature of the Seyfert 1 galaxy IRAS 20044-6114 (NGC 6860)

The physical conditions in the ionized gas, the stellar population, and the kinematics of the Seyfert 1 galaxy IRAS 20044-6114 (NGC 6860) are studied by high spatial resolution optical imaging and optical and near-IR spectroscopy of this luminous IR source. The broadband images show a compact nucleus, two weak spiral arms, a bar, a bulge, an inner ring, and a possible outer ring. The I-alpha image reveals bright emission-line regions associated with the Seyfert nucleus and an inner ring of intense star formation. The forbidden O III 5007-A image shows that the high-excitation gas is elongated perpendicularly to the direction of the bar, and reveals a bright compact object at about 40 arcsec NE of the nucleus which is undetectable in the broadband images. This object is interpreted as a dwarf young H II galaxy. The optical, near-IR, and FIR results show clear evidence that the nuclear and circumnuclear regions have composite and complex structure: a variable Seyfert 1 nucleus embedded in an intense and dusty star formation. environment.

Lipari, Sebastian↗

NASA NTRS1993

Omega from the anisotropy of the redshift correlation function in the IRAS 2 Jansky survey

Peculiar velocities distort the correlation function of galaxies in redshift space. In the linear regime, the distortion has a characteristic quadrupole plus hexadecapole form, with amplitude depending on the cosmological density parameter Omega. I report here measurements of the anisotropy of the correlation function in the IRAS 2 Jy redshift survey. The inferred value of Omega is Omega = 0.5 + 0.5 or - 0.25.

Hamilton, A. J. S.↗

NASA NTRS1993

Molecular gas in powerful radio galaxies detected by IRAS

The present CO(J = 1 to 0) line survey of powerful radio galaxies has led to the detection of five sources in eight IRAS-determined radio galaxies. The range of the computed molecular gas masses is 1-7 times the H2 mass of the Milky Way and strikingly contrasts with the low molecular gas masses found in radio-quiet FIR-selected elliptical galaxies. These new CO observations lend support to the hypothesis that powerful radio galaxies result from disk galaxy collisions that evolve into gas-rich, peculiar E/S0 galaxies in the course of their merging.

Mazzarella, J. M.↗

NASA NTRS1993

Circumstellar shells resolved in IRAS survey data. II - Analysis

IRAS survey data for 512 red giant stars and young planetary nebulae were processed using a computer program which fitted the data to an idealized model of a circumstellar shell. Seventy-six of these stars were found to have circumstellar shells resolved in the 60-micron survey data. Forty pct of the 76 stars are carbon stars. Thirteen are Mira variables. The evolution of these shells, involving the interaction of the expelled material with the ISM, is modeled, and the results suggest that the period during which Mira variables lose mass lasts for approximately 10 exp 5 yr. Carbon stars are found to shed mass for about 2 x 10 exp 5 yr. The expansion velocity of the outer shell for the largest shells will normally be lower by a factor of 3-5 than the expansion velocity obtained from CO observations.

Young, K.↗

NASA NTRS1993

Circumstellar shells resolved in the IRAS survey data. I - Data processing procedure, results, and confidence tests

We have examined the IRAS 60 and 100 micron survey data covering 512 evolved stars and young planetary nebulae for evidence of spatially resolved structure. A simple model, consisting of a central unresolved source surrounded by a resolved isothermal shell, was fitted to the data for each star. Seventy-six stars were found to be resolved in the 60 micron data. Tests have been performed to verify that the extended structure seen is not an artifact of the data-processing algorithm.

Young, K.↗

NASA NTRS1993

Magnetic fields in massive cloud cores - Comparison of MILLIPOL and IRAS results

The MILLIPOL polarimeter has been used to obtain 30-arcsec resolution 1300-micron data toward 10 cloud cores; the seven that were detected are associated with compact H II regions in massive molecular clouds. Cloud-core axis ratios and position angles were derived by examining the morphologies of IRAS-traced dust opacity structures. The MILLIPOL-detected cloud cores exhibit 1.5-3.2 core axis ratio values. The magnetic field is found to be generally perpendicular to the core dust distributions.

Kane, Brian D.↗