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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

The Solar Neighborhood. XXV. Discovery of New Proper Motion Stars with 0.40 sec/yr > mu > or = 0.18 sec/yr Between Declinations -47 deg and 00 deg

We present 2817 new southern proper motion systems with 0.40 sec/yr > mu > or = 0.18 sec/yr and declination between 47 deg and 00 deg. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main-sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems--SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc--are anticipated to be within 10 pc. We also find 23 new white dwarf (WD) candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with mu > or = 0.18 sec/yr and R(sub 59F) < or = 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (9 within 10 pc), 46 WDs (10 within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.

LOW MASS STARS↗
NASA NTRS2021

Detection of an extremely strong magnetic field in the double-degenerate binary merger product HD 144941

HD 144941 is an extreme He (EHe) star, a rare class of subdwarf OB star formed from the merger of two white dwarf (WD) stars. Uniquely amongst EHe stars, its lightcurve has been reported to be modulated entirely by rotation, suggesting the presence of a magnetic field. Here we report the first high-resolution spectropolarimetric observations of HD 144941, in which we detect an extremely strong magnetic field both in circular polarization (with a line-of-sight magnetic field averaged over the stellar disk〈Bz〉 ∼ −8 kG) and in Zeeman splitting of spectral lines (yielding a magnetic modulus of〈B〉 ∼17 kG). We also report for the first time weak Hαemission consistent with an origin an a Centrifugal Magnetosphere (CM). HD 144941’s atmospheric parameters could be consistent with either a subdwarf or a main sequence (MS) star, and its surface abundances are neither similar to other EHe stars nor to He-strong magnetic stars. However, its Hαemission properties can only be reproduced if its mass is around 1 M⊙, indicating that it must be a post-MS object. Since there is no indication of binarity, it is unlikely to be a stripped star, and was therefore most likely produced in a WD merger. HD 144941 is therefore further evidence that mergers area viable pathway for the generation of fossil magnetic fields.

M E Shultz↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - Cool stars with hot secondaries

A hot companion to the G5 III star HR 3080, a single-line spectroscopic binary, has been discovered from spectra in the vacuum-ultraviolet. The companion must be a subdwarf or pre-white dwarf. A list of previously known systems of the zeta Aur and VV Cep type observed with the ultraviolet spectrograph on Skylab is also given.

Parsons, S. B.↗
NASA NTRS1976

The astrometric binary Mu Cassiopeiae - Photographically almost resolved

Photographic observations of the Population II subdwarf astrometric binary Mu Cas are described which almost resolve the components and permit an estimate of their magnitudes and separation. Red- and blue-light photographs of the system were taken during an observing period when the component separation was maximum. The separation of the two components is estimated to be about 1.5 arcsec, position angles of about 194 and 201 deg are determined for the two years of the observing period, and the apparent magnitude of the faint companion is found to be approximately 10.

Feibelman, W. A.↗
NASA NTRS1978

A hot subluminous star - HDE 283048

The star HDE 283048 located at alpha = 3(h)50(m)3, delta = +25 deg 36 min shows a strong ultraviolet continuum. Ground-based observations indicate a hot-dominated composite spectrum. Several lines of evidence suggest that the hot component is a hot subdwarf.

Laget, M.↗
NASA NTRS1978

IUE observations of hot stars - HZ43, BD +75 deg 325, NGC 6826, SS Cygni, Eta Carinae

During the commissioning phase of IUE observations were made of a selection of hot stars: the white dwarf HZ43, the hot subdwarf BD +75 deg 325, the nucleus of the planetary nebula NGC 6826, the dwarf nova SS Cygni, and the peculiar object Eta Carinae. The observations were made in the low dispersion mode and the data have been reduced using a preliminary calibration. The results are presented and discussed for each object.

Heap, S. R.↗
NASA NTRS1981

Discovery of the molecular hydrogen ion (h2(+)) in the planetary nebulae

Low-dispersion spectra of fifteen planetaries and hot subdwarfs were obtained with the short wavelength prime camera on IUE and continuous flux distributions corrected for interstellar extinction were derived. Several planetaries, particularly the young planetaries of high surface brightness, show anomalous flux distributions. The most anomalous case is NGC 6210. These anomalies may be explained as absorption by H2+ H2(+) in the nebula.

Heap, S. R.↗
NASA NTRS1979

Middle- and far-ultraviolet observations of hot white dwarfs

Observations of HD 149499 B, the previously unrecognized white dwarf star found by the Skylab ultraviolet objective-prism survey, are discussed. Spectra of the binary HD 149499 AB were obtained by the short wavelength and long wavelength cameras of the IUE, and converted into fluxes. The absorption line strengths of the white dwarf secondary indicate a He/H composition ratio greater than or equal to 1. Comparison with model atmospheres of the IUE data suggests a temperature of around 93,000 K for HD 149499 B, while comparison with visual magnitude data indicates a temperature of 82,000 K. Either temperature value would make the star the hottest white dwarf for which reasonably reliable temperature estimates are available. Future work intended includes the repetition of the Skylab ultraviolet experiment on Spacelab for the detection of a complete sample of hot white dwarfs and subdwarfs.

Parsons, S. B.↗
NASA NTRS1981

Anomalous extinction in the planetary nebula Abell 30

The stellar continuous energy distribution from 8000 to 1250 A in Abell 30 is quite peculiar. The observed flux can be understood if a hot central star (approximately 200,000 K) is immersed in an absorbing dust cloud which has anomalous absorption with its peak near 2470 A. The dust nebula is a strong infrared source, maintained by conversion of the stellar UV flux. The internal reddening is E(B - V) = 0.30 mag and reaches 2.5 mag at 2470 A; it is best matched not by graphite but by laboratory observations of carbon smoke. Intense P Cygni lines show that a strong stellar wind exists. The central star may be an O subdwarf, approaching more nearly a helium-carbon degenerate DO.

Greenstein, J. L.↗
NASA NTRS1982

Special types of B stars

The properties of the Beta Cephei stars are examined with emphasis on spectral types, luminosities, periods, and light and velocity variations. Typical members of the group and their position in the observational and theoretical HR diagram are discussed. Those B stars with anomalous spectra (chemically peculiar) are considered including hot subdwarfs, extreme helium, weak helium, strong helium, helium variable, magnetic and mercury-manganese stars.

Lesh, J. R.↗
NASA NTRS1982

An ultraviolet investigation of the unusual eclipsing binary system FF AQR

A series of seven low dispersion IUE exposures in ultraviolet and wavelength regions obtained on December 6, 1981 during the eclipse of the subdwarf, during egress, and out of eclipse is analyzed. These observations and the binary phase at which they were made are shown on a schematic representation of the V-band light curve obtained in 1975. The depth in V is 0.15 mag. The circles are IUE V magnitudes from FES measures obtained during the observing run. They indicate an eclipse depth some 0.05 mag lower than expected, possibly due to difficulties with the color term in the FES calibration. The eclipse depths of Dworetsky in U, B and V were assumed in the calculations.

Dorren, J. D.↗
NASA NTRS1982

Ultraviolet observations of four symbiotic stars

Observations were obtained with the International Ultraviolet Explorer (IUE) of four symbiotic stars. The UV spectra of YY Her, SY Mus, CL Sco, and BX Mon are characterized by varying degrees of thermal excitation. These low resolution spectra have been analyzed in terms of line-blanketed model atmospheres of early A, B, and F type stars in order to identify the nature of the hot companion in these systems. The expected emission from early main sequence stars does not fully explain the observed distribution of UV continuum energy over the entire IUE spectral range (1200-3200 A). More likely the observed continuum may be originating from an accretion disk and/or hot subdwarf that photoionizes circumstellar material, and gives rise to the high excitation lines that have been detected. The Bowen fluorescent excited lines of O III in SY Mus exhibit slightly broadened profiles that suggest possible turbulent motions in an extended circumstellar cloud with characteristic velocities of approximately 300 km/s.

Michalitsianos, A. G.↗
NASA NTRS1981

Mass loss from interacting close binary systems

The three well-defined classes of evolved binary systems that show evidence of present and/or past mass loss are the cataclysmic variables, the Algols, and Wolf-Rayet stars. It is thought that the transformation of supergiant binary systems into the very short-period cataclysmic variables must have been a complex process. The new evidence that has recently been obtained from the far ultraviolet spectra that a certain subclass of the Algols (the Serpentids) are undergoing fairly rapid evolution is discussed. It is thought probable that the remarkable mass outflow observed in them is connected with a strong wind powered by accretion. The origin of the circumbinary clouds or flat disks that probably surround many strongly interacting binaries is not clear. Attention is also given to binary systems with hot white dwarf or subdwarf components, such as the symbiotic objects and the BQ stars; it is noted that in them both components may be prone to an enhanced stellar wind.

Plavec, M. J.↗
NASA NTRS1982

IUE observations of the peculiar star RX Puppis

The first set of high-dispersion UV observations of RX Pup are presented. Anomalous line profile structure observed in a number of high-excitation emission lines is discussed in context with a model that includes streams and complex mass motions in the system. Anomalies in high-excitation lines suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The continuum in low dispersion is fairly flat around 1200-2000 and rises toward longer wavelengths, and cannot be due to a star earlier than A0 II. Alternatively, it may be from an accretion disk. Photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature 75,000-90,000 K. Alternatively, it may be due to an accretion disk around a secondary with boundary layer temperature about 100,000 K.

Kafatos, M.↗
NASA NTRS1982

A large scale height galactic component of the diffuse 2-60 keV background

The diffuse 2-60 keV X-ray background has a galactic component clearly detectable by its strong variation with both galactic latitude and longitude. This galactic component is typically 10 percent of the extragalactic background toward the galactic center, half that strong toward the anticenter, and extrapolated to a few percent of the extragalactic background toward the galactic poles. It is acceptably modeled by a finite radius emission disk with a scale height of several kiloparsecs. The averaged galactic spectrum is best fitted by a thermal spectrum of kT about 9 keV, a spectrum much softer than the about 40 keV spectrum of the extragalactic component. The most likely source of this emission is low luminosity stars with large scale heights such as subdwarfs. Inverse Compton emission from GeV electrons on the microwave background contributes only a fraction of the galactic component unless the local cosmic ray electron spectrum and intensity are atypical.

Iwan, D.↗
NASA NTRS1982

The peculiar star RX Puppis

The first high dispersion observations of RX Puppis in the wavelength region 1200-3200 A were obtained with the International Ultraviolet Explorer. The anomalies observed in lines such as He II, semiforbidden C III, C IV, semiforbidden N III, semiforbidden N IV, semiforbidden O III, and semiforbidden Si III, which show split line profiles and Doppler displaced components, suggest dynamic activity in circumstellar material that probably has the form of rings and/or gas streamers between the cool giant and the hot companion. The Mg II lines show P-Cygni structure arising in the Mira primary. The continuum cannot be due to a star earlier than AO II and it may arise in an accretion disk around the hot secondary. Moreover, the line emission requires photoionization either from a hot subdwarf or the inner accretion disk.

Kafatos, M.↗
NASA NTRS1982

The symbiotics as binary stars

According to the original definition, symbiotic stars have combination spectra, in which the high-excitation emission lines regularly found in planetary nebulae are superposed on a low-temperature absorption spectrum. In connection with this investigation, the coexistence of a He II emission with the TiO absorption bands is also postulated. Attention is given to a summary of observed properties of symbiotics, binaries with a late-type giant component, possible models for the symbiotics, models with an accreting main-sequence star (Algol symbiotics), T Coronae borealis as a possible cataclysmic Algol-type symbiotic, binaries with rejuvenated degenerate dwarfs (novalike symbiotics), questions regarding the existence of PN symbiotics or subdwarfs unpowered by accretion, and related binary systems which are not symbiotics.

Plavec, M. J.↗
NASA NTRS1983

Secondary standard stars for absolute spectrophotometry

Based on an adopted absolute spectral energy distribution for the primary standard star Alpha Lyrae, absolute fluxes are given for the four very metal-deficient F type subdwarfs HD 19445, HD 84937, BD + 26.2606 deg, and BD + 17.4703 deg. Somewhat inferior data are also given for HD 140283. The data are given for 40-A bands and cover the wavelength range from 3080 A to 12,000 A. The four stars, all near magnitude 9 and distributed around the sky, are intended as secondary standards for absolute spectrophotometry.

Oke, J. B.↗