Engineering topics

Mcbreen, B.

Publications and source records attributed to Mcbreen, B..

16 records

NASA NTRS1986

Multiband far-infrared observations of the NGC 6334 complex

Multiband far-infrared (20-155 microns) observations of the large H II region/molecular cloud complex NGC 6334 are presented. The observations were performed simultaneously in four bands with effective wavelengths 21, 42, 71, and 134 microns. Eight far-infrared sources were detected which cover the range from sources with little of no continuum radio emission to well-developed H II regions. Maps of dust temperature and far-infrared optical depth of the complex are presented which reveal large-scale variations in the color temperature and optical depth. Star formation in the complex is discussed and it is concluded that a Rayleigh-Taylor instability generated by the gravitational attraction of the galactic plane can explain the regular separation of the far-IR sources.

Loughran, L.↗

NASA NTRS1985

GeV gamma-ray astronomy telescopes with high angular resolution

Gamma-ray telescopes flown on satellites have poor angular resolution with typical point source error circles of a few square degrees. It is shown that a major improvement in angular resolution for the detection of gamma-rays in the GeV region can be obtained with a single crystal as converter. The electron produced by a gamma ray incident at a small angle to a major crystal axis or plane is captured into channeling and radiates gamma rays. The channeling radiation and the electron-positron pair can be detected and yield point source locations with a precision of 5 arcseconds at 10 GeV. This is an improvement of three orders of magnitude on the angular precision of telescopes sensitive to gamma-rays above 50 MeV flown on Satellites.

Mcbreen, B.↗

NASA NTRS1985

Far-infrared spectrum of IRC + 10216

Far-infrared observations of IRC + 10216 in the wavelength range 20-160 microns are presented. The observations were performed simultaneously in four bands with effective wavelengths of 21, 42, 73, and 135 microns, respectively. The scan profile across the source at 21 microns is found to be wider than that for a point source. Interpreting the far-infrared spectrum on the basis of a model in which circumstellar grains are heated by a central source, the radial density dependence is r exp -2, and the emissivity dependence is lambda exp -n, it is found that n = 1-1.2. Time variations of a smaller magnitude at longer wavelengths as compared to the variation at near-infrared wavelengths can also be understood on the basis of this model. Using the mass-loss rate derived from CO observations, the mass absorption coefficient of the grains at 100 microns is found to be not less than 40/sq cm g.

Rengarajan, T. N.↗

NASA NTRS1985

Far-infrared observations of two southern H II regions - RCW 122 and G 351.6-1.3

The luminosities in excess of 1,000,000 solar luminosities obtained in the present 1-arcmin resolution mapping of the two southern H II regions RCW 122 and G 351.6-1.3 requires the presence of OB star clusters. A luminosity/unit mass of the associated cloud of about 6 solar luminosities/solar mass is obtained by combining near-IR, far-IR, and CO-emission properties for RCW 122, and it is determined that the emitting dust grains are amorphous silicate-like. G 351.6-1.3 has very similar properties, although the fraction of 1-25 micron luminosity corrected for silicate absorption is about five times less than for RCW 122.

Mcbreen, B.↗

NASA NTRS1984

High-resolution far-infrared observations of the extended W51 complex

A far-IR map with 1 arcmin resolution was obtained of the W51 H II region molecular cloud complex. The 40-120 microns survey was performed to study embedded sources which excite the H II gas. The far-IR emission distribution overlapped radio emissions from the region, implying that the extended dust clouds were heated by the same sources as the H II regions. Four compact sources were characterized and associated with concentrations of luminosities that suggested a scarcity of low-mass stars. The brightest source, labeled W51-I, has a luminosity/mass ratio of 150, high enough to indicate a burst of massive O star formation. No triggering mechanism was identified for the burst of star formation.

Rengarajan, T. N.↗

NASA NTRS1984

Far-infrared and CO observations of the W33 complex

The giant H II region W33 is a strong radio continuum source. However, it has received little attention compared to the nearby M17 region. The present investigation is concerned with the results of 1 min resolution far-infrared (far-IR) and CO observations of the W33 region. The complex has been resolved into several components at the far-IR wavelengths, and information has been obtained regarding spectral characteristics in the range from 20 to 250 microns. An examination is conducted of the nature of the individual W33 sources and their relationship to the radio sources and the molecular clouds. Particular attention is given to the nature of the unusual source W33 A which has a very high ratio of far-IR to radio luminosity.

Stier, M. T.↗

NASA NTRS1984

Far-infrared observations of a star-forming region in the Corona Australis dark cloud

A high-resolution far-IR (40-250-micron) survey of a 0.9-sq-deg section of the core region of the Corona Australis dark cloud (containing very young stellar objects such as T Tauri stars, Herbig Ae and Be stars, Herbig-Haro objects, and compact H II regions) is presented. Two extended far-IR sources were found, one associated with the Herbig emission-line star R CrA and the other with the irregular emission-line variable star TY CrA. The two sources have substantially more far-IR radiation than could be expected from a blackbody extrapolation of their near-IR fluxes. The total luminosities of these sources are 145 and 58 solar luminosity, respectively, implying that the embedded objects are of intermediate or low mass. The infrared observations of the sources associated with R CrA and TY CrA are consistent with models of the evolution of protostellar envelopes of intermediate mass. However, the TY CrA source appears to have passed the evolutionary stage of expelling most of the hot dust near the central source, yielding an age of about 1 Myr.

Cruz-Gonzalez, I.↗

NASA NTRS1984

Far-infrared sources in the vicinity of the supernova remnant W28

The W28 supernova remnant molecular cloud complex has been surveyed in the 40-250 micron spectral range with a three-sigma sensitivity of 100-165 Jy per beam. Only two sources have been found. One, located near the center of the SNR, has a luminosity of 54,000 solar luminosities and can be identified with the thermal radio source G6.6-0.1. The energizing source is probably an O-type ZAMS star. The second source, which is near the boundary of the SNR at a sharp gradient of OH absorption, has a luminosity of 6000 solar luminosities and has no radio counterpart. It is best explained as a B1 ZAMS star or a pre-main sequence object presumably formed from the impact of an expanding SNR with a molecular cloud. No far-IR emission is observed at the position of the CO molecular cloud, which seems to have been impacted by the SNR.

Odenwald, S. F.↗

NASA NTRS1983

Far-infrared and CO observations of NGC 6357 and regions surrounding NGC 6357 and NGC 6334

Two 1.7 square degree sections of the galactic plane at 70 microns have been surveyed with one-arcminute resolution. The scanned areas included the giant southern H II region complexes NGC 6357 and NGC 6334. Nineteen far-infrared sources were observed. The sources range in luminosity from 16,000 to 550,000 solar masses. Far-infared continuum and CO line observations of NGC 6357 are presented. Four far-infrared sources were found in this complex and for one of these sources the exciting stars are identified. Far-infrared and CO observations of sources in the field surrounding NGC 6357 and NGC 6334 are presented. The far-infrared sources coincide frequently with CO line temperature peaks. The CO clouds which surround the far-infrared sources have similar CO-13 column densities. Two of the far-infrared sources in the field have associated OH and H2O maser emission and compact H II regions.

Mcbreen, B.↗

NASA NTRS1982

High resolution far-infrared observations of the evolved H II region M16

A balloon-borne telescope was used to map NGC 6611, and three far-IR sources embedded in an extended ridge of emission were detected. It is found that Source I is an unresolved far-IR source, embedded in a molecular cloud, which despite the association of an H2O maser with its source does not exhibit radio continuum emissions. Far-IR sources II and III are associated with ionized gas-molecular cloud interfaces, with the far-IR radiation arising from dust at the boundary heated by the OB cluster. These observations are consistent with models of the later stages of evolution of an H II region.

Mcbreen, B.↗

NASA NTRS1982

Far-infrared observations of the evolved H II region M16

The results of far infrared (FIR) observations of the larger H II region M16, associated with the young open star cluster NGC 6611, are discussed. Three FIR sources detected on an extended ridge of FIR emission within the scanned region are described. The observations confirm that M16 is an H II region in a late stage of evolution. The H II region has expanded and is now extremely density bounded, consisting of an extended region of ionized gas and a series of ionization fronts located at the surrounding molecular cloud boundaries nearest to the exciting OB star cluster. The FIR radiation arises from heated dust at these boundaries.

Mcbreen, B.↗

NASA NTRS1980

The far-infrared size of IRC +10216

IRC +10216, a carbon star undergoing extensive mass loss, has been observed with a broad-band far-infrared (40-250 micron) photometer on the CFA/UA 102 cm balloon-borne telescope. From repeated scans, the deconvolved FWHM size of IRC +10216 was determined to be 0.92 arcmin plus or minus 0.15 arcmin. Based on this size, models for the density distribution of the dust in the surrounding cloud indicate that there is more dust at large radii than would be predicted by a 1/r-squared density distribution and that the mass-loss rate of the central source was twice its current value only 2000 years ago.

Fazio, G. G.↗

NASA NTRS1979

Evidence for a variable far-infrared source in NGC 6334

NGC 6334 has been mapped with a 40-250 micron photometer with 1 arcmin resolution. Six sources of far-infrared radiation have been detected. The second-strongest source was not detected in an earlier (2.7 years) 40-350 micron survey of the same region. This source is interpreted as a variable far-infrared source. The new source, located at the position of OH and H2O maser sources, is extended (0.7 arcmin FWHM) and has a bolometric luminosity of 190,000 solar luminosities and may represent a hitherto unobserved transient stage of protostellar collapse.

Mcbreen, B.↗

NASA NTRS1975

Change in the high-energy radiation from the Crab

On 1973 July 23, the Cornell gamma-ray telescope had a second exposure to the Crab Nebula and pulsar via balloon flight from Palestine, Texas. On the previous flight, 1971 October 6, the signal from the pulsar had been unmistakably clear, especially at the highest energies (above 800 MeV), and an unpulsed component of similar average power had also been discernible. On the second flight, despite higher altitude, longer exposure, and improved electronics, the pulsed signal was barely detectable and the dc component not observable at all. The drop in intensity seems to increase with energy, being only a factor of 2 at 200 MeV but an order of magnitude at 1 GeV. There is some indication (not compelling) that the gamma-ray flux may have changed even within the 6-hour exposure. The first flight may have viewed the Crab in a state of enhanced high-energy emission correlated with the glitches that occurred on 1971 August 1 and October 25.

Greisen, K.↗

NASA NTRS1975

Upper limits of hard gamma-ray emission from six X-ray sources

The Cornell 100-inch gamma-ray telescope has been used to set upper limits for the gamma-ray flux above 400 MeV from the X-ray sources Cyg X-1, Cyg X-2, Cyg X-3, Cas A, Cas B, and Per X-1. An upper limit for the diffuse flux of the galactic disk was set which is consistent with OSO-3 and SAS-2 data. A new measurement of the atmospheric gamma-ray generation rate is presented.

Campbell, M.↗

NASA NTRS1973

Pulsed high-energy gamma rays from the Crab Nebula.

Review of recorded data on the pulsed radiation detected by the Cornell 100-inch gas-Cerenkov gamma-ray telescope within 1 degree of the Crab Nebula in direction, at hundreds of MeV up to more than 1 GeV, coincident in time with optical pulses from NP 0532. A main pulse and a secondary pulse are shown to contain about an equal number of events and display evidence of being narrower than at lower energies. There is weak evidence for further pulse structure in the interval between these two peaks, and also for an unmodulated gamma-ray component about equal to the time-averaged pulsed flux.

Mcbreen, B.↗