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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The UV resonance lines of three hot Ap stars: HD 133029, HD 175362 and HD 219749

High resolution spectra of the Ap stars HD 133929, HD 175329 and HD 219749 were obtained during two 16 hour shifts with the IUE satellite at Goddard Space Flight Center. Stellar wind, extended atmosphere in rigid corotation with the stellar surface, and the influence of the strong magnetic field on the upper part of the atmosphere would explain the shape and the strength of the resonance lines. The resonance lines of HD 175362 in particular show very peculiar behavior. The necessary driving forces for the expanding envelope are not compatible with the diffusion theory of the Ap atmospheres.

Rakos, K. D.↗
NASA NTRS1992

The nature of dust around the post-asymptotic giant branch objects HD 161796 and HD 179821

Ground-based 7.4-24-micron spectra of two post-AGB objects, HD 161796 and HD 179821, are reported, and they are compared to those of other preplanetary nebulae. HD 161796 and HD 17982 show emission features at 10-12 microns and at 10 microns, and they exhibit a very rapid increase in flux between 13 and 15.5 microns. In view of the O-rich photosphere of HD 161796 and the presence of OH maser emission around all three objects, these features are ascribed to various oxides. The observed spectral features are quite different from the canonical silicate features observed in most O-rich giants. It is argued that HD 161796 and the bipolar nebulae Roberts 22 and NGC 6302 have all undergone the third dredge-up, with most of the dredged-up carbon having been converted to nitrogen by envelope-burning. It is concluded that carbon-rich grain material, produced during the interval between the end of the third dredge-up and the moment when envelope burning finally reduced the C/O ratio below unity again, could be responsible for the UIR bands now being excited in Roberts 22 and NGC 6302.

Justtanont, K.↗
NASA NTRS1988

HD 115781 and HD 116204 - Two RS CVn binaries

HD 115781 and HD 116204 (BL CVn and BM CVn) are shown to be RS CVn binaries with periods near 20 days. HD 115781 is double-lined. The primary type is about K1 III, while the secondary is probably a late-type subgiant. The masses of the two components are equal within observational error. HD 116204 is also of type K1 III. It shows exceptionally strong Ca II H and K emission, together with an emission-line spectrum typical of RS CVn stars in the IUE ultraviolet region, but H-alpha is an absorption line. The secondary star in the HD 116204 system has not been detected.

Griffin, R. F.↗
NASA NTRS1979

The total scattering cross sections for H2 + H2, D2 + D2, and HD + HD for relative collision energies below 10 meV

Relative total scattering cross sections for normal H2 + normal H2, para-H2 + para-H2, normal D2 + normal D2, ortho-D2 + ortho-D2, and HD + HD were measured at energy below 10 meV by colliding particles from two inclined nozzle beams. Cross sections for the H2 + H2 pairs were measured over a relative velocity range of 200-1450 m/s; the normal H2 + normal H2 results suggest a l = 3 orbiting resonance near 375 m/s while the para-H2 + para-H2 results have a l = 4 orbiting resonance near 585 m/s. This latter resonance has a peak energy of 1.79 meV and a FWHM of 1.05 meV. The D2 + D2 cross sections were measured over the velocity range of 190 to 1000 m/s and a minimum between the l = 4 and l = 5 orbiting resonances was observed. Some preliminary measurements on HD + HD over the range of 250-1250 m/s indicate a possible l = 4 orbiting resonance near 300 m/s. The experimental work compares favorably to cross sections calculated from a theoretical potential.

Johnson, D. L.↗
NASA NTRS1985

HD 160538 and HD 185510 - Two active-chromosphere stars with hot companions

Short-wavelength ultraviolet spectra of two active-chromosphere giants, HD 160538 and HD 185510, show hot stellar continua and L-alpha absorption features. The hot companion of HD 160538 is a white dwarf whose ultraviolet spectrum is matched best to the energy distribution of a T(eff) = 30,000 K and log g = 8 model atmosphere. The ultraviolet spectrum of HD 185510 shows numerous absorption features and is identified as a B subdwarf. Since the giant star of each of these binary systems has no known abundance anomalies, these systems appear to be consistent with the mass-transfer scenario of barium-star formation.

Fekel, F. X.↗
NASA NTRS1990

High-velocity interstellar gas in the lines of sight to the Wolf-Rayet stars HD 97152 and HD 96548

The interstellar medium was studied in the direction to the WR stars HD 96548 and HD 97152, and the results are reported. New observational data on the UV spectra of several field stars near both these WR stars are presented. The high-velocity gas seen in the spectra of these stars suggests that the detected expanding interstellar gas structure consists of two OB cluster supershells. The presence of high-velocity absorption components in one of five field star spectra in the direction of the more isolated WR star HD 96548 suggests that this expanding gas does not originate from the optical ring nebula RCW 58 surrounding HD 96548, as previously believed, but instead indicates the detection of a previously unknown expanding interstellar shell in this line of sight.

Nichols-Bohlin, Joy↗
NASA NTRS2007

Variability of Disk Emission in Pre-Main Sequence and Related Stars. I. HD 31648 and HD 163296 - Isolated Herbig Ae Stars Driving Herbig-Haro Flows

Infrared photometry and spectroscopy covering a time span of a quarter century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the exception of a major increase in emitted flux in a broad wavelength region centered near 3 pm in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 pm region throughout this span of time. In both stars the changes in the 1-5 pm flux indicate structural changes in the region of the disk near the dust sublimation zone, possibly causing its distance from the star to vary with time. Repeated thermal cycling through this region will result in the preferential survival of large grains, and an increase in the degree of crystallinity. The variability observed in these objects has important consequences for the interpretation of other types of observations. For example, source variability will compromise models based on interferometry measurements unless the interferometry observations are accompanied by nearly-simultaneous photometric data.

Sitko, Michael L.↗
NASA NTRS2008

Variability of Disk Emission in Pre-main-sequence and Related Stars. I. HD 31648 and HD 163296: Isolated Herbig Ae Stars Driving Herbig-Haro Flows

Infrared photometry and spectroscopy covering a time span of a quarter-century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the exception of a major increase in emitted flux in a broad wavelength region centered near 3 micron in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 micron region throughout this span of time. In both stars, the changes in the 1-5 micron flux indicate structural changes in the region of the disk near the dust sublimation zone, possibly causing its distance from the star to vary with time. Repeated thermal cycling through this region will result in the preferential survival of large grains, and an increase in the degree of crystallinity. The variability observed in these objects has important consequences for the interpretation of other types of observations. For example, source variability will compromise models based on interferometry measurements unless the interferometry observations are accompanied by nearly simultaneous photometric data.

Sitko, Michael L.↗
NASA NTRS1990

The discovery of magnetically controlled circumstellar matter in the helium-weak stars HD 5737 and HD 79158

The paper reports the discovery, using combined IUE spectroscopy and Zeeman polarimetric magnetic field measurements, of magnetically controlled circumstellar material in two helium-weak stars. HD 5737 = Alpha Sculptoris is, except for its extreme helium deficiency, similar to the He weak sn star HD 21699. A unique period for the magnetic and C IV and Si IV variations of 21.65 days is reported. The effective (longitudinal) field nulls coincide extremely well with C IV line strength maxima. The magnetic field and equatorial trapped plasma are highly oblique to the rotation axis (about 70 deg), and the line variations appear to be stable. Similar magnetospheric variations in HD 79158 = 36 Lyncis have been discovered, for which no period had been previously available. The period is 3.84 days, yet it too displays magnetic-equatorial plasma. The magnetospheric axis is highly oblique to the rotation axis, around 80 deg.

Shore, Steven N.↗
NASA NTRS1981

Far-ultraviolet energy distributions of the metal-poor A stars HD 109995 and HD 161817

Low-resolution IUE spectra at wavelengths between 1300 and 3400 A of the metal-poor stars HD 109995 (A1p) and HD 161817 (A4p) have been compared with model-atmosphere energy distributions computed by Kurucz (1979). Good overall agreement is found. Effective temperatures, metal abundances, and angular diameters could be determined. Assuming an absolute visual magnitude of 0.7, the previously determined gravity log = 3 yields masses of 0.5 solar masses for both stars. It is found that the theoretical UBV colors calculated earlier agree reaonably well with the ones observed for these stars.

Boehm-Vitense, E.↗
NASA NTRS1984

Variable polarization in X-ray binaries - HD 153919 (= 4U1700 - 37) and HD 152667 (= OAO1653 - 40?)

Variable linear polarization has been observed in the optical radiation from two presumed X-ray binary systems, HD 153919 (= 4U1700 - 37) and HD 152667 (probably not OAO1653 - 40). This intrinsic polarization appears correlated with the orbital phase of the binary, but the polarimetric light curve shows variations from year to year. The Stokes parameter q, u light curves are consistent with the polarization being caused by the Rayleigh scattering of light from the primary by gas streams in the vicinity of the secondary. Several orbital and physical parameters of the binary systems are derived from the polarimetric observations.

Dolan, J. F.↗
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 NTRS1990

HD 43246 and HD 127208 - Two unusual F-G + B binary systems

New optical spectroscopic observations along with ultraviolet IUE observations have been obtained for the two interacting F or G III + B V binaries: HD 43246 and HD 127208. Photometric observations indicate random changes superimposed on regular ellipsoidal light variations, the latter probably the result of tidal distortion of the giant primaries. Mass transfer and loss is apparent in inverted mass ratios derived from orbital analysis, strong wind features present in the spectra, and the presence of circumsystem shells. Regular and irregular changes in the spectral features are discussed in this context.

Dempsey, Robert C.↗
NASA NTRS1999

Cometary Dust in the Debris Disks of HD 31648 and HD 163296: Two "Baby" (BETA) Pictoris Stars

The debris disks surrounding the pre-main-sequence stars HD 31648 and HD 163296 were observed spectroscopically between 3 and 14 microns. Both stars possess a silicate emission feature at 10 microns that resembles that of the star beta Pictoris and those observed in solar system comets. The structure of the band is consistent with a mixture of olivine and pyroxene material, plus an underlying continuum of unspecified origin. The similarity in both size and structure of the silicate band suggests that the material in these systems had a processing history similar to that in our own solar system prior to the time that the grains were incorporated into comets.

Sitko, Michael L.↗