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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
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NASA NTRS1987

Cataclysmic variables. Recent multi-frequency observations and theoretical developments; Proceedings of the 93rd IAU Colloquium, Bamberg, West Germany, June 16-19, 1986

Papers are presented on the formation and evolution of low-mass close binaries with compact components, the periods of cataclysmic variables, multiwavelength observations of dwarf novae during outbursts, and radio emission from cataclysmic variables. Also considered are long-term optical photometry of the dwarf nova VW Hyi, periodic modulations in the optical light curves of EX Hydrae, and Echelle-Mepsicron time-resolved spectroscopy of the dwarf nova SS Cygni. Other topics include UV and X-ray observations of cataclysmic variables, new EXOSAT observations of TV Columbae, accretion disk evolution, and the boundary layer in cataclysmic variables.

Drechsel, H.↗
NASA NTRS1976

The nature of the X-ray nova A0620-00

A model is presented for the X-ray nova A0620-00. Identification with a nova can be ruled out on two counts. A binary consisting of a late-type subgiant near the Roche lobe, irradiated by an accreting compact companion is shown, however, to be in agreement with all known observations. Photometry of the optical object should be pursued since variability on an approximately eight hour period is expected.

Endal, A. S.↗
NASA NTRS1978

Extreme-ultraviolet observations of dwarf novae from Apollo-Soyuz

The paper reports on EUV observations of four dwarf novae (SS Cyg, Z Cha, VW Hyi, and AE Aqr) in July 1975 during the Apollo-Soyuz Test Project, which were performed by using pointed grazing-incidence optics and a channel-electron multiplier as a photon detector. An EUV flux in the range from 55 to 150 A was detected from SS Cyg during an optical outburst at an intensity level considerably below that of Rappaport et al. (1974). Upper limits are placed on the EUV fluxes from Z Cha, VW Hyi, and AE Aqr. Multicolor optical photometry of SS Cyg and AE Aqr is also examined which was obtained simultaneously with the EUV observations. It is concluded that intrinsic EUV flux variability is probably a characteristic of SS Cyg and that the same system exhibits an extremely large range of soft X-ray luminosities while remaining at about the same visible light level. Several models for the SS Cyg system are compared with the EUV data.

Margon, B.↗
NASA NTRS1979

The optical counterpart of GX 339-4, a possible black hole X-ray source

Optical studies of the galactic X-ray source GX 339-4 (4U 1658-48), which led to its recent identification as reported by Doxsey et al. (1979), are presented. Reddening and distance estimates are given, as well as evidence for optical variability on differing time scales. The emission-line spectra and UBV photometry suggest that GX 339-4 may be at about 8 kpc and have a main-sequence B star binary companion. Both the optical spectrum and optical/X-ray luminosity ratio for GX 339-4 may be similar to Cir X-1.

Grindlay, J. E.↗
NASA NTRS1987

CAL 83 - A puzzling X-ray source in the Large Magellanic Cloud

Spectroscopic observations of the X-ray point source no. 83 in the Columbia Astrophysics Laboratory Einstein survey of the Large Magellanic Cloud have been accumulated over 4 yr. The optical spectrum shows no stellar absorption features, but only emission lines typical of an accretion disk. Radial velocity measurements reveal a small (K = 30 km/s) velocity variation modulated at 0.93 d, which appears to be the orbital period. No strong constraints can be put on the mass of the collapsed object, but its companion must be a low-mass, evolved star. Evidence for a precessing disk with a possible period of 69 days is presented. Exosat X-ray observations reveal no short-term (less than 6 hr) periodicities, although erratic, random variations were observed. The X-ray spectrum is very soft, reminiscent of some of the candidate black-hole sources. IUE ultraviolet spectra show only weak emission lines of N V and He II. The UV flux is variable with a mean effective temperature of about 19,000 K. Optical B, V photometry during November 1985 showed random variations of about 0.2 mag with a mean V = 17.3 mag.

Crampton, David↗
NASA NTRS1985

Multifrequency observations of dwarf novae outbursts

Studies using EXOSAT and IUE data combined with ground-based optical and IR photometry, spectroscopy and polarimetry of the transition timescales and physical properties of the high accretion rate states of the disks in cataclysmic variables are discussed. Implications for dwarf novae stem from comparison of the timing and amplitude of the optical and IR rise with that of the UV and X-ray; the development of the optical and UV line profile changes as the outburst develops; and the similarity of the outburst flux distributions in different systems and different types of outbursts (standstills and supermaxima). These features of dwarf novae outbursts present interesting comparisons with the outbursts of systems like TV Col and GK Per.

Szkody, P.↗
NASA NTRS1974

Nonperiodic optical flickering in HZ Herculis

High-speed simultaneous dual-channel photometry of HZ Her and a nearby comparison star reveal nonperiodic optical flickering in the HZ Her system on a time scale of 15 to 300 sec. The amplitude of the flickering appears to be correlated with orbital phase. Optical emission from a hot spot in a disk of material around the X-ray source cannot account for the flickering.

Moffett, T. J.↗
NASA NTRS1983

Observations of suspected low-mass post-T Tauri stars and their evolutionary status

The results of a study of five X-ray discovered weak emission pre-main-sequence stars in the Taurus-Auriga star formation complex are presented. All are of spectral type K7-M0, and about 1-2 mag above the main sequence. One is a double-lined spectroscopic binary, the first spectroscopic binary PMS star to be confirmed. The ages, masses, and radii of these stars as determined by photometry and spectroscopy are discussed. The difference in emission strength between these and the T Tauri stars is investigated, and it is concluded that these 'post-T Tauri' stars do indeed appear more evolved than the T Tauri stars, although there is no evidence of any significant difference in ages.

Mundt, R.↗
NASA NTRS1978

Ultraviolet observations and the extended spectrum of NGC 4151

Five-channel ultraviolet photometry of the Seyfert galaxy NGC 4151 was obtained at three epochs with the ANS. These data are combined with other recent results to illustrate the spectrum of the nucleus of NGC 4151 from 34 microns to 20 MeV, with corrections for galaxy contamination. It is found that no other part of the spectrum has a slope like the best-fitting power law for the X-rays. The C IV emission-line flux is measured; the C IV/H-beta ratio is between 5 and 8, which is similar to the ratio in quasars.

Wu, C.-C.↗
NASA NTRS1976

Simultaneous X-ray and optical observations of X Persei

Photoelectric photometry of X Persei was obtained on five out of seven consective nights in January 1975, from the Lick and Leuschner Observatories. The observations yield B = 6.848 + or - 0.002, B-V = 0.139 + or - 0.001, with no strong evidence for variability during the observing run. These are the faintest and bluest photoelectric magnitudes and colors ever reported for X Per; this change apparently occured relatively uniformly during 1973-74 and is reminiscent of behavior last observed in approximately 1900. The suggested association of X Persei with the weak X-ray source 3U 0352+30 raises the possibility of detection of X-ray/optical covariability. On January 21, 1975, 7 hours of data were obtained from both observatories simulataneous with OAO Copernicus X-ray observations of 3U 0352+30. The X-ray data varied during this period by a factor of two, but there is no obviously correspondent optical activity, to a level of 0.02 mag. The optical data are also used to limit to 0.01 mag variations coincident with the X-ray periodicity.

Margon, B.↗
NASA NTRS1982

BL Lac objects and their associated galaxies

CCD photometry of five BL Lac objects indicates that at least three, and possibly four, are located at the centers of giant elliptical galaxies. The redshift for one of these objects, 1218+304, is estimated. A lower limit is placed on the redshift of 1219+28, for which no associated galaxy has been detected. Separation of the galaxy emission from the total observed flux makes possible comparison of the optical - far red flux from the point source alone with radio and X-ray data. This comparison suggests the emission from 1727+50 and 1218+304 can be interpreted as due to direct synchrotron emission. Observations of a small group of galaxies associated with the BL Lac object 1400+162 are also discussed.

Weistrop, D.↗
NASA NTRS1981

Extremely red compact radio sources - The empty field objects

Radiation of 10 microns has been detected from 1413+135, one of the very red objects discovered by Rieke, Lebofsky, and Kinman (1979) at near-infrared wavelengths. The spectrum of this object flattens at wavelengths longer than 2.2 microns. Upper limits are also given for the 10-micron emission from 2255+14, 0026+34, and 0406+121. Photometry between 1.25 and 2.2 microns confirms the variability of 1413+135, 2255+41, and 0406+121. Five percent resolution spectra of 1413+135 and 0406+121 between 1.5 and 2.4 microns show no emission or absorption lines. The spectral data rule out the possibility that 1413+135 is a quasar with normal line strengths and a redshift less than 1.3 and greater than 4. The lack of features of the 1.5-2.4-micron spectra, the rapid variability, and the overall shape of the radio, infrared, and X-ray energy distributions are consistent with a BL Lac nature for these objects.

Beichman, C. A.↗
NASA NTRS1980

Phase variability in the rapid optical oscillations of SS Cygni

High-speed photometry of SS Cygni on four nights during the 1978 September eruption revealed a small-amplitude optical oscillation with period 8.23 s and mean semiamplitude 0.0005 mag on September 21 and period 8.50 s and mean semiamplitude 0.0006 mag on September 23. If the observed periods present orbital periods near the surface of the white dwarf, then the white dwarf mass must exceed 0.92 solar mass. Phase variability of the oscillation is analyzed quantitatively and found to be less than that observed in 1978 June for soft X-ray pulsations from SS Cygni.

Horne, K.↗
NASA NTRS1988

Design of the Extreme Ultraviolet Explorer long-wavelength grazing incidence telescope optics

Designing optics for photometry in the long-wavelength portion of the EUV spectrum (400-900) A) poses different problems from those arising for optics, operating shortward of 400 A. The available filter materials which transmit radiation longward of 400 A are also highly transparent at wavelengths shortward of 100 A. Conventional EUV optics, with grazing engles of less than about 10 deg, have very high throughput in the EUV, which persists to wavelengths shortward of 100 A. Use of such optics with the longer-wavelength EUV filters thus results in an unacceptably large soft X-ray leak. This problem is overcome by developing a mirror design with larger graze angles of not less than 20 deg, which has high throughput at wavelengths longer than 400 A but at the same time very little throughput shortward of 100 A.

Finley, David S.↗
NASA NTRS1983

Infrared observations of RS CVn stars

The paper presents infrared photometry of the RS CVn binary stars AR Lac (1.2-10 microns) and MM Her (1.2-3.5 microns) as they egressed from their primary and secondary eclipses; of the eclipsing systems RS CVn and Z Her at maximum light (1.2-10 microns) and of the non-eclipsing systems UX Ari and HR 1099 (1.2-10 microns). An analysis of these and published V data based on flux ratio diagrams (linear analogues of color-color diagrams) shows that G and K stars supply the infrared light of these systems. In AR Lac, the combined light of a G5-K0 subgiant and either a late F dwarf or an early F subgiant can account for the observed visual and infrared light curves. None of these systems shows infrared emission from circumstellar matter. This result is simply understood: dust grains would not be expected to form in the physical conditions surrounding the subgiant, and the corona and chromosphere (whose properties have been deduced from spectroscopic X-ray observations) should not produce appreciable infrared emission.

Berriman, G.↗
NASA NTRS1978

The nature of Aquila X-1

Photometry in the UBV spectra was used to observe Aquila X-1. This X-ray source, usually producing flux on the order of 1-10% that of the Crab Nebula, often behaves in a manner resembling the behavior of galactic X-ray stars. A description of the calibration methods used in the observations is presented, with attention to photoelectric-photographic methods. These observations suggest a quiescent spectral class near Ko, i.e., a dwarf at a distance of 1.6 kpc. The more intense X-ray emissions are said to be generated from internal heating of the stellar atmosphere, with additional energy supplied by a low-mass companion star. This explaination is at variance with the semi-detached Roche model.

Margon, B.↗
NASA NTRS1979

Support for joint infrared and Copernicus X-Ray observations of Cygnus X-3

Simultaneous X-ray and infrared measurements were carried out of the flares from Cygnus X-3 from the Copernicus spacecraft observatory. The detectors, InSb, were arranged so that 1.65 and 2.2 micrometer broadbend photometry was performed through a common diaphragm. The measurements were used to determine the energy distribution during a flare and thus learn about the infrared spectrum and its changes during the flare.

Source record↗
NASA NTRS1979

UBV photometry of SMC X-2

UBV measurements of the proposed optical counterpart of the X-ray source SMC X-2 show no variability. We suggest that SMC X-2 is similar to the galactic transient sources with early-type counterparts.

Schlosser, W.↗