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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 127 records · Page 7
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NASA NTRS1985

Niobium in R And (S6, 6e) and HR 1105 (S5, 3)

Lines of the first multiplet of niobium are strong in R And and HR 1105. These lines are also present in other S stars: HR 8714, R Cam, V Cnc, R CMi, and T Sgr. They are also visible in the M stars, Beta-Peg and Mu-UMa. An approximation to the abundance ratio, Nb/Fe, has been deduced from pairs of lines having nearly equal intensity. In R And, the ratio is about 200 times the solar value. It is hoped that good plates will soon be obtained for the near infrared region, so that the significant Nb/Rb abundance ratio may be determined.

Davis, D. N.↗
NASA NTRS1986

IUE observations of the dwarf novae OY Car in superoutburst

The May 1985 superoutburst of OY Car, an eclipsing member of the SU UMa subclass of dwarf novae, was observed extensively with IUE to obtain phase-resolved spectra throughout several orbital cycles, when the superhump was well developed and lay close in phase to the eclipse. The UV lines and continuum vary with orbital phase and show a strong UV eclipse coincident with the optical eclipse. This implies that the superhump source at eclipse is not a strong contributor in the ultraviolet. The UV emission line spectrum and lack of X-ray eclipse suggest the presence of an extended coronal region. The flux evolution observed is unusual in that gross changes occur during the decline from superoutburst. The later spectra actually appear hotter than spectra earlier in the decline, and suggest that, early on, the inner disk is obscured from view.

Hassall, B. J. M.↗
NASA NTRS1986

A spectroscopic study of the cataclysmic binary star SU Ursae Majoris

Spectroscopic observations of SU UMa, the prototype of a class of short-period cataclysmic binaries, are reported. The orbital period is found to be 0.076351 + or - 4.3 x 10 to the -5th days. The velocity amplitude of the emission line source is 58 + or - 4 km/s, leading to a mass function of about 0.0015 solar mass and implying a moderately low inclination. The line cores in H-alpha and H-beta lead the wings slightly in orbital phase, contrary to the predictions of simple hot spot models of the line core. The velocity widths of the Balmer series increase toward higher members of the series, suggesting that pressure broadening may contribute nonnegligibly to the emission line widths.

Thorstensen, John R.↗
NASA NTRS1987

BE Ursae Majoris - A detached binary with a unique reprocessing spectrum

New infrared photometry, optical and UV spectrophotometry, and a photographic ephemeris are presented for the detached binary BE UMa. Results show the primary to be a DO white dwarf with an effective temperature of 80,000 + or - 15,000 K and a mass of 0.6 + or - 0.1 solar masses. No evidence is found for variability of the primary. The main-sequence secondary star is shown to be of early-M spectral type, with a formal range of M1-M5 being possible. A reflection effect in reprocessed line and continum radiation is produced by EUV radiation from the primary incident on the secondary atmosphere. It is suggested that the temperature of the reprocessed component of the secondary's atmosphere is in the 5000-8500 K range, and that emission lines of decreasing ionization form deeper in the irradiated envelope. Relatively narrow He II and high-excitation metal lines are formed from recombination and continuum fluorescence processes.

Ferguson, Donald H.↗
NASA NTRS1987

BE Ursae Majoris: A detached binary with a unique reprocessing spectrum

New infrared photometry, optical and UV spectrophotometry, and a photographic ephemeris are presented for the detached binary BE UMa. Results show the primary to be a DO white dwarf with an effective temperature of 80,000 + or - 15,000 K and a mass of 0.6 + or - 0.1 solar masses. No evidence is found for variability of the primary. The main sequence secondary star is shown to be of early M spectral type, with a formal range of M1 to M5 being possible. A reflection effect in reprocessed line and continuum radiation is produced by EUV radiation from the primary incident on the secondary atmosphere. It is suggested that the temperature of the reprocessed component of the secondary's atmosphere is in the 5000 to 8500 K range, and that emission lines of decreasing ionization form deeper in the irradiated envelope. Relatively narrow He II and high excitation metal lines are formed from recombination and continuum fluorescence processes.

Ferguson, Donald H.↗
NASA NTRS1987

Chromospheric-coronal activity at saturated levels

High-resolution IUE observations of Mg II emission lines in W Ursae Majoris were obtained. In addition, estimates of the Mg II emission for other F-type contact binaries were obtained using archival high-resolution k line spectra and some nonstandard methods; the available data were compiled for Mg II, C IV, and X-ray emission in main-sequence F, G, K, and M dwarfs in order to determine the upper levels of radiation from their chromospheric-coronal plasma. The high-resolution IUE observations of Mg II h and k emission lines in W UMa indicate that both components of the contact binary have similar chromospheres, confirming the many earlier low-resolution light curve studies. The Mg II emission (L Mg II)/Lbol) of contact binaries correlates with the Rossby number (R0), forming an extension of single G-K dwarfs.

Vilhu, Osmi↗
NASA NTRS1988

White dwarfs in cataclysmic variables - Low state IUE observations of V794 Aquilae, MR Serpentis, and AN Ursae Majoris

IUE low-dispersion observations of one novalike system (V794 Aql) and two AM Her systems (MR Ser and AN UMa) during low or intermediate-low accretion-rate states are reported. The decreased UV emission during these times was used to place limits on the white dwarf temperatures. When these results are added to the existing data on white dwarf temperatures, it appears that the white dwarfs in systems with normal high accretion rates and only occasional low-accretion-rate states remain hotter than the white dwarfs in systems with low average accretion rates.

Szkody, Paula↗
NASA NTRS1988

Simultaneous Exosat and VLA observations of the contact binaries VW Cephei and XY Leonis - Quiescent emission and a flare on VW Cephei

Two W UMa-type contact binaries, XY Leo and VW Cep, were observed simultaneously with Exosat, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P about 0.27 days); however, no orbital modulation of either the X-ray or 6 cm data was seen for either star, indicating large emitting regions. A large flare from VW Cep was detected, the best such simultaneous flare data ever obtained from a star other than the sun. Its behavior before, during, and after the flare was remarkably similar to that found in solar flares, although at 6 cm this flare on VW Cep was about 10,000 times more luminous than typical strong solar flares. For both stars, it is demonstrated that the 6 cm emission cannot be the result of bremsstrahlung radiation of the X-ray emitting plasma; in fact, it is shown, in the case of the VW Cep flare, that the 6 cm emission is consistent with gyrosynchrotron radiation from a source region of order of the system separation.

Vilhu, Osmi↗
NASA NTRS1988

Millisecond optical photometry of the DQ Herculis objects

The results of millisecond optical photometry of the DQ Herculis stars EX Hya, H2252-035, V1223 Sgr, and AE Aqr obtained at the Las Campanas Observatory and Cerro Tololo Inter-American Observatory during the years 1985, 1986, and 1987 are reported. The data for coherent and incoherent features are searched for. Coherent features (other than those previously known) were not detected for frequencies between 0.1 and 250 Hz at 4-sigma upper limits of 0.05-0.4 percent. Evidence is not found for 1-3 s, quasi-coherent features. Such features have been detected in the optical emission of the AM Her objects AN UMa, EF Eri, and E1405-451. Because of the similarities between AM Her and DQ Her objects, it was suggested that such quasi-coherent features might also be found in the DQ Her objects.

Imamura, James N.↗
NASA NTRS1988

Modulated mass-transfer model for superhumps in SU Ursae Majoris stars

The response of a circular accretion disk to rapid modulation of the mass-transfer rate into the disk is explored in order to model superhumps in SU UMa stars. It is proposed that periodically enhanced flow may disrupt or heat up the outer disk and produce the dips noted just before the superhump peaks. The elliptical accretion-disk model with extended vertical disk structure can account for the observed characteristics of superhumps in these stars.

Mineshige, Shin↗
NASA NTRS1989

500-3200 A observations of the interacting binary stars V356 Sgr and Beta Lyr

Results on VG356 Sgr and Beta Lyr are presented from the Voyager UV spectrometers and the IUE. The observations of V356 Sgr cover two eclipses in which the total strength of the UV emission lines were invariant. At wavelengths shorter than 1600 A, an uneclipsed UV continuum was found. A model for the origin of the circumstellar matter in V356 Sgr is given. The UV observations of Beta Lyr show a strong far-UV continuum down to 912 A. The spectral shape fo the far-UV continuum closely resembles that of a UX Uma-type cataclysmic variable. Analysis of the Beta Lyr data indicates that the central object is small, with a radius on the order of 1 solar radius or less.

Polidan, R. S.↗
NASA NTRS1990

Masses and radii for thirteen chromospherically active ellipsoidal variables

The amplitude of the ellipticity effect, the mass function, and the V sin i in ten long-period RS CVn SB1 binaries are used to compute limits on the masses of the two stars and the radius of the primary: zeta And, UV CrB, V1764 Cyg, V826 Her, V350 Lac, GX Lib, V1197 Ori, AP Psc, 33 Psc, and EE UMa. Explicit masses and radii are computed for three SB2 systems: BL CVn, V1817 Cyg, and TZ Tri. The primary in several is found to fill 95 percent or more of its Roche lobe. The two minima produced by the ellipticity effect are unequal in depth, with the effect largest when i is near 90 deg and the primary nearly fills its Roche lobe. The greatest inequality found, in UV CrB, was 0.08 mag.

Hall, Douglas S.↗
NASA NTRS1991

PG0027 + 260 - An example of a class of cataclysmic binaries with mysterious, but consistent, behavior

This paper reports extensive optical observations on the PG0027 + 260 binary, carried out on August 1984 with the 1.3 McGraw-Hill telescope and Mark II spectrometer at Michigan-Dartmouth-MIT Observatory on Kitt Peak. It is shown that this object is an eclipsing novalike variable with an orbital period of 3.51 hr. The PG0027 + 260 displays several unexplained phenomena which are remarkably similar to those of the SW Sex, DW UMa, and V1315 Aql, which are eclipsing novalike stars with periods between 3 and 4 hrs. The eclipse of the PG0027 + 260 is modeled, and it is shown that, while the mean eclipse light curve is easy to match, there is no simple explanation for the variable depth.

Thorstensen, John R.↗
NASA NTRS1990

IRAS observations of extended dust envelopes around evolved stars

Deconvolved IRAS profiles, with resolution 2-3 time better than detector sizes 1.5 and 3 arcmin at 60 and 100 microns, are presented for a number of evolved stars with extended emission. These include VY UMa, Mu Cep, S Sct, U Hya, Y CVn, U Ant, alpha Ori, Y Pav, UU aur, IRC + 10216, RZ Sgr, and R Lyr. Simple models suggest that extended IRAS emission results from stars which greater mass loss rates in the past, rather than from stars with large current mass loss rates.

Hawkins, George↗
NASA NTRS1991

Digging in the coronal graveyard - A Rosat observation of the red giant Arcturus

A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream.

Ayres, Thomas R.↗
NASA NTRS1992

Periodic variability in the optical counterpart of X-ray Nova Muscae 1991

Analysis of over 1000 CCD images of the optical counterpart of the black hole candidate Nova Muscae 1991, taken 3-5 months after the initial outburst, reveal the existence of a luminosity hump of about 0.2 mag which recurs every 10.5 hr. This period presumably either is, or is closely related to, the orbital period, which is thus similar to that of the confirmed black hole system A0620 - 00. The light-curve shape, the lack of significant color variations, and marginal evidence for a change in the recurrence period suggest that the luminosity humps in Nova Muscae may be related to the superhump phenomenon in the SU UMa subclass of dwarf novae. Other implications of the analogy between soft X-ray transients and dwarf novae are discussed.

Bailyn, Charles D.↗
NASA NTRS1993

IUE observations of cataclysmic variable

Twenty two approved International Ultraviolet Explorer (IUE) programs were studied over a 14 year period. These programs are listed. The observations and subsequent analysis centered on cataclysmic variables (close binaries with a late main sequence star transferring material to a primary white dwarf via an accretion disk). The early studies highlighted the flux distribution of the accretion disk at outburst and quiescence, while later studies accomplished time-resolved observations throughout the orbital cycles, the study of the outflowing winds present at outburst, the study of the white dwarf in those systems with low accretion rate. There are 39 publications resulting from this work which are listed. These results include those for individual systems (Stepanian's star, Lanning 10, AM Her, MV Lyr, TV Col, VW Hyi, T Leo, IR Gem, TT Ari, Z Cam, BV Pup, IP Peg, PG1030+590, V1315 Aql, SW UMa, V426 Oph, WZ Sge, BY Cam, and U Gem) as well as review articles in journals and publications from reviews at meetings that summarize the impact of IUE on the study of accretion disks, white dwarfs, and hot spots resulting from stream impact as well as magnetic accretion columns.

Szkody, Paula↗