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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 469 records · Page 26
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NASA NTRS1988

The 1985 May superoutburst of the dwarf nova OY Carinae. II - IUE and Exosat observations

Ultraviolet (IUE) and X-ray (Exosat) observations of the eclipsing dwarf nova OY Carinae during the superoutburst of May 1985 are presented. From the lack of X-ray eclipse and UV behavior, it is deduced that the X-ray flux originates in an optically thin corona comparable in size to the Roche lobe, and not directly from the white dwarf or boundary layer. The asymmetric UV line emission originates partly in the accretion disk and partly in a wind. There is a strong modulation of the UV continuum flux that is thought to be caused by extended vertical disk structure shadowing the inner regions.

Naylor, T.↗
NASA NTRS1987

Hydrodynamic studies of oxygen, neon, and magnesium novae

Results are presented from recent theoretical studies that have examined the properties of nova outbursts on ONeMg white dwarfs. These outbursts are much more violent and occur much more frequently than outbursts on CO white dwarfs. Hydrodynamic simulations of both kinds of outbursts are in excellent agreement with the observations.

Starrfield, Sumner↗
NASA NTRS1988

Photometry and spectroscopy of a newly discovered polar - Nova Cygni 1975 (V1500 CYG)

The paper reports photometric and spectroscopic observations which led to the conclusion that Nova Cygni 1975 (V1500 Cyg) is a polar (of AM Her-type).The CCD photometry confirms the constancy of the photometric period which is again interpreted as an orbital cycle. The time-resolved MMT spectra make it possible to reconstruct, under several assumptions, the basic system parameters: M1=0.9M solar mass and M2=0.31M solar mass.

Kaluzny, Janusz↗
NASA NTRS1988

Optical and ultraviolet observations of nova Vul 1987

The outburst for a nova discovered in Nov. 1987 and followed since then is summarized. Although it was possible to observe it with the IUE at maximum, its ultraviolet energy faded rapidly, and after the first 2 weeks it was impossible to observe it at IUE wavelengths. It is observed to form a thick dust shell and is in the nebular stage.

Starrfield, S.↗
NASA NTRS1988

IUE observations of the 1987 superoutburst of the dwarf nova Z Cha

Low resolution IUE observations of the dwarf nova Z Cha during superoutburst are presented. These cover most of the development of the outburst and have sufficient time resolution to probe continuum and line behavior on orbital phase. The observed modulation on this phase is very similar to that observed in the related object OY Car. The results imply the presence of a cool spot on the edge of the edge of the accretion disk, which periodically occults the brighter inner disk. Details of the line behavior suggest that the line originated in an extended wind-emitting region. In contrast to archive spectra obtained in normal outburst, the continuum is fainter and redder, indicating that the entire superoutburst disk may be geometrically thicker than during a normal outburst.

Harlaftis, E.↗
NASA NTRS1989

Analysis of NOVA-1 Doppler data

The intent is to prepare a set of Doppler tracking data for the NOVA-1 Satellite to be included in a data base of satellite tracking data. This data base is to be used in a solution for the gravity field of the Earth. This new gravity field model is needed so that the orbit of the proposed TOPEX (Ocean TOPography EXperiment) satellite can be determined accurately enough for the satellite's missions to be accomplished.

Felsentreger, T. L.↗
NASA NTRS1988

On the outburst recurrence time for the accretion disk limit cycle mechanism in dwarf novae

An attempt is made here to elucidate the dwarf nova outburst time scale in terms of basic physics, and to place limits on the model by using the observed recurrence times. A simple analytical model is developed to describe the limit cycle process, and an expression is obtained for the interval between eruptions. It is shown that the smallness of the amount of mass accreted onto the central white dwarf during eruption can be explained in terms of the propagation of heating and cooling fronts. The dependency of the fraction of the disk mass accreted on the model parameters is derived, and the result is used to construct a semianalytic expression for the recurrence time.

Cannizzo, John K.↗
NASA NTRS1989

Slow expansion of the shell of the recurrent nova T Pyxidis and detection of a faint extended envelope

New H-alpha narrow-based CCD imaging of the recurrent nova T Pyxidis and the detection of a very faint, extended H-alpha halo surrounding the already known shell are reported. A forbidden O III image containing an emitting shell with a morphology different from that of the H-alpha shell is presented, and measurements of the H-alpha shell expansion are reported which rule out the 1966 eruption date for the shell origin, assuming uniform expansion. It is proposed that the observed shell consists of slowly moving, solar abundance ejecta which are photoionized.

Shara, Michael M.↗
NASA NTRS1988

On a polar Nova Cygni 1975 (V1500 Cyg)

Einstein X-ray observations of Nova Cygni 1975 (V1500 Cyg) are reported, including the discovery that this system is a polar. It is suggested that AM Her-type systems (polars) and DQ Her-type systems (intermediate polars) are the extremes of a continuum of magnetic binaries. Such objects as BG CMi, EX Hya and V1500 Cyg and possibly TV Col, AE Aqr, and CP Pup, whose appearance depends on individual properties and geometry, are intermediate between the two classes.

Chlebowski, Tomasz↗
NASA NTRS1989

Evidence for a high-mass white dwarf in nova V1500 Cygni 1975

Time-resolved spectroscopy of V1500 Cyg are presented from 1981, when the nebular lines from the nova ejecta had faded sufficiently to permit reliably radial velocity measurements on emission lines from the binary remnant. The spectra possess a typical AM Herculis signature. The wavelength region 3800-5100 A contains a number of strong lines, in particular the Balmer series and He II 4686 A. All lines show periodic velocity changes with the same period as the photometric variations. On the first night the lines are relatively weak and narrow, are in phase with the photometric cycle, and suffer extreme modulation; two months later they are strong and broad, are roughly 90 deg out of phase with the photometric cycle, and have relatively less variation in their line fluxes. These features support the suggestion that the remnant is an AM Her system. The observed radial velocity of the secondary is 193 + or - 9 km/s. Various constraints suggest that the magnetic white dwarf in this system has a mass over 0.9 solar.

Horne, Keith↗
NASA NTRS1989

The 1989 outburst of V404 Cygni: A very unusual x ray nova

On May 22, 1989, the Japanese Ginga Team discovered a new x ray source that was cataloged as GS 2023+338. This source was subsequently identified as coincident in position with a previously known nova cataloged as V404 Cygni. Its last recorded outburst was in 1938 when it rose to about 12th mag. Spectroscopic data were obtained and confirmed the nature of the outburst. Additional ground based data were obtained by us at CTIO and the VLA. The x ray behavior of this object was reported to be very unusual and it reached a peak of about 17 crab about one week after discovery. Since then it has varied widely in magnitude at all wavelengths at which it has been studied. A brief summary of the observations that were obtained up to the time of the meeting and shortly thereafter is presented.

Wagner, R. M.↗
NASA NTRS1989

Viscous evolution of accretion discs in the quiescence of dwarf novae

Viscous evolution of accretion disks in the quiescence of dwarf novae is investigated semi-analytically. There are two key factors: the inward flow of the initial mass in the disk and the diffusion of the material added into the disk. The results are compared with the brightness temperature distributions obtained by the eclipse mapping of Z Cha and OY Car. The functional form of the viscosity parameter a, its values, the types of outbursts, and the application to soft X-ray transients are discussed.

Mineshige, Shin↗
NASA NTRS1990

Orbital periods of recurrent novae

The class of recurrent novae (RN) with thermonuclear runaways contains only three systems (T Pyx, U Sco, and V394 CrA), for which no orbital periods are known. This paper presents a series of photometric observations where the orbital periods for all three systems are discovered. T Pyx is found to have sinusoidal modulation with an amplitude of 0.08 mag and a period of 2.3783 h (with a possible alias of 2.6403 h). U Sco is found to be an eclipsing system with an eclipse amplitude of roughly 1.5 mag and an orbital period of 1.2344 days. V394 CrA is found to have sinusoidal modulation with an amplitude of 0.5 mag and a period of 0.7577 days. Thus two out of three RN with thermonuclear runaways (or five out of six for all RN) have evolved companions.

Schaefer, Bradley E.↗
NASA NTRS1989

Sublimating icy planetesimals as the source of nucleation seeds for grain condensation in classical novae

The problem of grain nucleation during novae outbursts is a major obstacle to our understanding of dust formation in these systems. How nucleation seeds can form in the hostile post-outburst environment remains an unresolved matter. It is suggested that the material for seeding the condensation of ejecta outflow is stored in a primordial disk of icy planetesimals surrounding the system. Evidence is presented that the requisite number of nucleation seeds can be released by sublimation of the planetesimals during outbursts.

Matese, John J.↗
NASA NTRS1990

Model atmospheres for the early stages of novae in outburst

For the photospheres of classical novae during the early stages of their outbursts, continuum and line blanketed models are presented. The expanding envelopes are characterized by small density gradients that lead to very large geometrical extensions and large temperature differences between inner and outer parts. The spectra show large excesses in the IR and small Balmer jumps which may either be in absorption or emission. For the parameters considered most lines are in absorption if powerlaw density distributions and radiative equilibrium are assumed. The effects of modifications in the temperature structure (e.g., heating from shock fronts) and in the density stratifications as well as changes in the abundances are discussed.

Wehrse, R.↗
NASA NTRS1990

Doppler imaging of the dwarf nova U Geminorum

Doppler tomography is applied to time-resolved spectra of the dwarf nova U Geminorum, and it is found that emission from the bright-spot region has neither the velocity of the gas stream nor the velocity of the disk along the stream but lies roughly midway between. It is shown that earlier observations of U Gem were consistent with the present results, and it is concluded that the line emission arises immediately after the shock as the gas from the stream mixes with the disk. The data also show evidence for Balmer emission from the secondary star which, together with the bright spot's emission, produces a complicated S-wave in trailed spectra.

Marsh, Thomas R.↗
NASA NTRS1991

Spectral transformation of the unusual variable star MWC560 to resemble a nova

A dramatic change has occurred in the ultraviolet spectrum of the emission-line star MWC560, so that it now closely resembles the spectrum of a nova shortly after outburst. This event may signal a major mass-ejection episode such as presumably occurred in past centuries in the symbiotic star R Aquarii to produce the well-known bipolar nebula, and it may herald the emergence of a standard symbiotic-star emission-line spectrum in MWC560, corresponding to a change in evolutionary state.

Maran, Stephen P.↗
NASA NTRS1992

TT Crateris - A long-period, double-lined dwarf nova

Time-resolved CCD photometry and spectroscopy of the dwarf nova TT Crt during quiescence are presented. The spectra reveal Balmer emission as well as absorption features of a K5-M0 secondary. The B, V, R light curves are dominated by a periodic variation of full amplitude 0.35 mag in V, which are interpreted as the ellipsoidal variation of the secondary star. The remarkably large amplitude indicates a high inclination (50-65 deg) and a massive white dwarf M greater than 0.8 solar mass. The ratio of the radial velocity semiamplitudes of the primary to the secondary is 0.5-1.4. The best period that can be determined from the observations is 438.17 minutes, with a possible alias at 445 minutes.

Szkody, Paula↗