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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
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NASA NTRS1994

The origin of the far-infrared luminosity within the spiral galaxy M101

High resolution 60 and 100 micron images obtained with the Infared Astronomical Satellite (IRAS) are compared with H alpha images in order to investigate the origin of the far-infrared luminosity within the late-type spiral galaxy M101. There is a good correspondence between the far-infrared and H-alpha morphology. The far-infrared and H-alpha luminosities have been measured at 129 independent locations on the star forming disk of M101. After correcting the H-alpha luminosity for extinction and extrapolating the IRAS (40-120 microns) luminosity to 1000 microns we find that the far-infrared luminosity is commensurate with that expected from the O and B stars which are required to ionize the hydrogen gas, at all locations within M101. Additionally, the IRAS HiRes 60 and 100 micron images reveal that the dust temperature peaks coincide identically with the location of H II regions. The far-infrared luminosity of M101 is radiated primarily by dust with temperatures well in excess of that expected for cirrus, but similar to that observed for Galactic and extragalactic H II regions.

Devereux, Nicholas A.↗
NASA NTRS1988

The small scale structure of the interstellar medium in the Orion association: The flotsam of star formation

The small scale dynamics and structure of the interstellar medium of the Orion OB1b, c association was studied using IUE high dispersion SWP and LWR/LWP spectra. The area surveyed centers on the Belt and encompasses the Orion Cloak. The dynamics and abundances of the ionized and warm neutral gas surrounding the central parts of the association are determined using 35 B stars. Results are compared with the picture of the Orion interstellar medium gained using COPERNICUS, especially for the structure and dynamics of the Orion Cloak.

Sonneborn, G.↗
NASA NTRS1985

The enigmatic star EZ Pegasi - A mystery solved?

EZ Peg, a ninth-magnitude G star that has been classified by various authors as an irregular variable, a U Gem system, and a contact binary, is shown to have all the spectroscopic and photometric characteristics of an active-chromosphere RS CVn binary. It is suggested that the reported outburst of 1943, when the spectrum appeared to be that of a B star, never occurred. The strong Ca II H and K reversals, viewed with low spectral resolution, caused the photospheric Ca II absorption to appear abnormally weak, mimicking a much earlier spectral type.

Howell, S. B.↗
NASA NTRS1981

Distribution of hot stars and hydrogen in the Large Magellanic Cloud

Far-UV brightness distribution data for the face of the Large Magellanic Cloud (LMC) are derived from calibrated electrographic imagery in the 1050-1600 and 1250-1600 A ranges, and far-UV fluxes for individual hot-star groupings in the LMC are compared with H-alpha measurements and with a 21-cm survey. It is found that large clouds of interstellar hydrogen contain smaller concentrations revealed by H-alpha emission and other clear regions where hot O-B stars excite no H II regions. Either (1) four of these associations lie behind the large interstellar clouds, or (2) the clouds may be very diffuse and extended in the line of sight. Six other peaks in far-UV flux not previously cataloged are also indicated.

Page, T.↗
NASA NTRS1987

Synthetic uvby-beta photometry of HD 12856 and HD 13890

Stromgren and H-beta colors have been measured from spectrophotometric observations of two Be stars without published photometry in Per OB1: HD 12856 (B0 pe) and HD 13890 (B1 III:pe). Stellar parameters and improved spectral types are then derived from the color indices and the calibrations of Jakobsen (1986). These are compared with the parameters of normal B stars and are used to estimate the evolutionary status of the stars.

Torres, A. V.↗
NASA NTRS2012

Wide-field Infrared Survey Explorer

We present WISE (Wide-field Infrared Survey Explorer) mid-infrared photometry of young stellar object candidates in the Canis Majoris clouds at a distance of 1 kpc. WISE has identified 682 objects with apparent 12 and 22 micron excess emission in a 7 deg x 10 deg field around the CMa Rl cloud . While a substantial fraction of these candidates are likely galaxies, AGB stars, and artifacts from confusion along the galactic plane, others are part of a spectacular cluster of YSOs imaged by WISE along a dark filament in the R1 cloud. Palomar Double Spectrograph observations of several sources in this cluster confirm their identity as young A and B stars with strong emission lines. In this contribution, we plot the optical -mid-infrared spectral energy distribution for the WISE YSO candidates and discuss potential contaminants to the sample . The data demonstrate the utility of WISE in performing wide-area surveys for young stellar objects.

Padgett, Deborah↗
NASA NTRS2006

Physical Conditions of Eta Car Complex Environment Revealed From Photoionization Modeling

The very massive star, Eta Carinae, is enshrouded in an unusual complex environment of nebulosities and structures. The circumstellar gas gives rise to distinct absorption and emission components at different velocities and distances from the central source(s). Through photoionization modeling, we find that the radiation field from the more massive B-star companion supports the low ionization structure throughout the 5.54 year period. The radiation field of an evolved O-star is required to produce the higher ionization . emission seen across the broad maximum. Our studies utilize the HST/STIS data and model calculations of various regimes from doubly ionized species (T= 10,000K) to the low temperature (T = 760 K) conditions conductive to molecule formation (CH and OH). Overall analysis suggests the high depletion in C and O and the enrichment in He and N. The sharp molecular and ionic absorptions in this extensively CNO - processed material offers a unique environment for studying the chemistry, dust formation processes, and nucleosynthesis in the ejected layers of a highly evolved massive star.

Verner, E. M.↗
NASA NTRS1992

Elemental abundances of the B and A stars Gamma Geminorum, 7 Sextantis, HR 4817, and HR 5780

Fine analyses of the B and A stars, Gamma Geminorum, 7 Sextantis, HR 4817, and HR 5780 are performed. Although the data cover rather limited spectral regions, still useful results were obtained. The data were mostly obtained at the KPNO coude feed telescope with CCD TI No. 3, camera 5, and grating A. The He/H ratio of HR 4817 confirms the similarity of many abundance values with those of the peculiar Mn star 53 Tauri. For the most part Gamma Gem, 7 Sex, and HR 5780 have derived abundances similar to those of other normal sharp-lined stars of similar effective temperature.

Adelman, Saul J.↗
NASA NTRS1982

Results from the Orbiting Astronomical Observatory. XLI - Photometry of M31 and M33

Filter photometry observations from the Orbiting Astronomical Observatory, in six wavelength bands between 1550 and 4250 A, are reported for several positions along the major and minor axes in M31 and at some positions in M33. The spatial resolution is 10 arcmin. The colors along the major axis of M31 within about 20 arcmin of the nucleus are similar to the nucleus; at 45 arcmin the colors are much bluer, indicating a spiral arm population. This behavior is expected from other observations of H I, CO, and early-type stars, which are all concentrated in a ring of material whose inner edge is about 7 kpc (= 35 arcmin) from the nucleus. The center of M33 is bluer than the ring of M31, and the arms of M33 even bluer. There are no colors too blue to be explained (within observational error) by unreddened B stars.

Davis, J.↗
NASA NTRS1987

Recurrent episodic mass loss in a B2e star - 66 Ophiuchi, 1982-1985

The results of three intensive ultraviolet monitoring campaigns for 66 Oph in September-October 1982, September 1983, and September 1984, supplemented by the available IUE archival data from April, 1982 to June, 1985 are reported. The stellar wind went through at least two and probably three episodes of weak-wind absorption. At wind minimum, the resonance profiles and equivalent widths of C IV, Si IV, Si III, and Al III are similar to those observed in normal B stars of comparable luminosity, effective temperature, and v sin i. The strong-wind absorption profiles show one or more shortward-shifted discrete components superposed upon the weak-wind absorption profiles. Significant profile variations are seen on time scales spanning over two orders of magnitude, ranging from small-amplitude changes detected on time scales of hours to the transitions from wind minimum to maximum, which take months.

Grady, C. A.↗
NASA NTRS1987

Synthetic filter photometry and evolutionary status of two Be stars in the association Per OB1

Stromgren and H-beta colors have been determined from spectrophotometric observations for two Be stars without published photometry in the association Per OB1: HD 12856 (B0 pe) and HD 13890 (B1 III:pe). Stellar parameters and improved spectral types are then derived from the color indices using the calibrations of Jakobsen (1986), and independently from the BCD classification method. The intrinsic properties of HD 12856 and HD 13890 are compared with those of normal B stars and are used to estimate their evolutionary status.

Torres, Ana V.↗
NASA NTRS1984

Absorption and Emission of EUV Radiation by the Local ISM

The Berkeley extreme ultraviolet radiation (EUV) telescope flown on the Apollo Soyuz mission in July, 1975 established the existence of a measurable flux of EUV (100 lambda or = or = 1000 A) originating from sources outside the solar system. White dwarfs, flare stars and cataclysmic variables were dicovered to be relatively intense compact sources of EUV photons. Moreover, this and other subsequent experiments have strongly suggested the presence of a truly diffuse component of the FUV radiation field possibly due to thermal emission from hot interstellar gas located in the general vicinity of the Sun. Closer to the H1, 912 A edge, the effect of a few hot O and B stars has been shown to be very important in establishing the interstellar flux density. All these results imply that the local interstellar medium (ISM) is immersed in a non-negligible EUV radiation field which, because of the strong coupling between EUV photons and matter, will play a crucial role in determining its physical structure. The available information on the local ISM derived from the limited EUV observations carried out so far is assembled and analyzed. These include measurements of the spectra of bright EUV sources that reveal clear evidence of H photo absorption at lambda 400 A and of the He ionization edge at 228 A.

Paresce, F.↗
NASA NTRS1983

Synthesis maps of ultraviolet observations of neutral interstellar gas

Copernicus and IUE measurements of neutral hydrogen column densities have been taken for about 140 stars distributed between 10 and 3000 pc from the sun and plotted in several maps to directly yield estimates of contours of neutral hydrogen column density in the 5-500 x 10 to the 17th/sq cm range. These maps show that low column density neutral hydrogen is asymmetrically distributed around the sun with a 'hole' in the neutral hydrogen located in the third quadrant. This distribution mirrors that of nearby B stars associated with the Gould belt. The maps clearly show the directions in which observations at wavelengths less than 912 A will be most successful.

Frisch, P. C.↗
NASA NTRS1995

10 micron spectroscopy of younger stars in the rho Ophiuchi cloud

Spectra in the 10 micrometer region were obtained of 14 young stars associated with the central core of the rho Oph dark cloud complex. Silicate dust emission and absorption features can be fairly well reproduced with simple models using the emissivity of the silicates in the Orion Trapezium region, believed to be typical of molecular cloud dust. A spectrum of the Trapezium star theta(sup 1) Ori D was obtained to define the emissivity more precisely. The emissivity of silicate dust around the late-type giant Mu Cep does not improve the fits to the absorption features and provides a poorer match to the emission features. None of the sources display a strong 11.2 micrometer peak like that seen in comet Halley and attributed to crystalline olivine. A broad weak feature near 11.2 micrometer, possibly related to the comet feature, may be present in the emission spectrum of the Herbig Ae star HD 150193. Absorption features toward two of the objects are narrower than would be expected from Trapezium-like silicates, suggesting differences in the composition of the silicates. The relation between the silicate extinction band depth and H2O ice band depths is determined for the deeply embedded objects. One late-type object, Elias 14, clearly shows the 11.25 micrometer aromatic hydrocarbon emission feature, possibly excited by the nearby B star, HD 147889, though the latter does not exhibit the feature.

Hanner, M. S.↗
NASA NTRS1981

The ultraviolet properties of dust in the Orion Nebula

The continuum in the Orion Nebula was observed with the IUE at 16 positions varying from 30 arcsec to 5 arcmin in angular separation from the central star Theta(1) Orionis C. The atomic continuum was estimated from the H-beta brightnesses. The remaining scattered starlight was analyzed by multiple-scattering models in which the main parameters are: (1) the albedo of the dust; (2) the scattering phase function parameter, the averaged cosine of the angle of scattering; and (3) the density of dust grains at small distances from the star. It is found that (a) dust must be depleted near the star; (b) the albedo is fairly well determined and is constant across the 2200 A extinction feature; and (c) grains are quite forward-throwing at 1300 A, as they have been found at 4600 A earlier. The scattering is more isotropic at 2400 A. However, the absolute value of the scattering phase function parameters at all wavelengths is quite uncertain because it depends sensitively upon the density of grains close to the star.

Mathis, J. S.↗
NASA NTRS1984

The resonance lines of Hg II in IUE spectra of chemically peculiar stars

Twenty IUE images of chemically peculiar (CP) stars are analyzed to demonstrate that the previously detected Hg II overabundances in CP stars is real. Attention was focused on the Hg II resonance lines at 1650 and 1942 A. A total of eight stars were scanned and spectrum synthesis computations were performed to characterize the model atmospheres for each object. The 1942 A line was found to be insensitive to effective temperature, microturbulence and isotopic mixture influences, and therefore well-suited to abundance analyses. A non-LTE process was ruled out as a source of the Hg anomaly. Finally, it is suggested that diffusion-type processes be attributed to Hg enhancements in main sequences B stars.

Leckrone, D. S.↗
NASA NTRS1981

Distribution of hot stars and hydrogen in the Large Magellanic Cloud

Imagery of the Large Magellanic Cloud (LMC), in the wavelength ranges 1050 to 1600 A and 1250 to 1600 A, was obtained by the S201 far ultraviolet camera during the Apollo 16 mission. These images were reduced to absolute far-UV intensity distributions over the area of the LMC, with 3 to 5 arc min angular resolution. Comparison of these far-UV measurements in the LMC with H sub alpha and 21 cm surveys reveals that interstellar hydrogen in the LMC is often concentrated in 100 pc clouds within 500 pc clouds. Furthermore, at least 25 associations of O-B stars in the LMC are outside the interstellar hydrogen clouds; four of them appear to be on the far side. Far-UV and mid-UV spectra were obtained of stars in 12 of these associations, using the International Ultraviolet Explorer. Equivalent widths of L alpha and six other lines, and relative intensities of the continuum at seven wavelength from 1300 A to 2900 A, were measured. These spectra are also discussed.

Page, T.↗
NASA NTRS1994

An IUE survey of interstellar H I Ly alpha absorption. 1: Column densities

We measure Galactic interstellar neutral hydrogen column densities by analyzing archival interstellar Ly alpha absorption line data toward 554 B2 and hotter stars observed at high resolution with the IUE satellite. This study more than doubles the number of lines of sight with measures of N(H I) based on Ly alpha. We have included the scattered light background correction algorithm of Bianchi and Bohlin in our data reduction. We use the correlation between the Balmer discontinuity (c sub 1) index and the stellar Ly alpha absorption in order to assess the effects of stellar Ly alpha contamination. Approximately 40% of the B stars with measured (c sub 1) index, exhibit serious stellar Ly alpha contamination. One table contains the derived values of the interstellar N(H I) for 393 stars with at most small amounts of stellar contamination. Another lists the observed values of total N(H I) for 161 stars with suspected stellar Ly alpha contamination and/or uncertain stellar parameters.

Diplas, Athanassios↗