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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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NASA NTRS1993

RE 1016-053 - A pre-cataclysmic binary, and the first extreme ultraviolet and X-ray detections of a DAO white dwarf

Photometric observations and analysis of the optical, UV, EUV, and X-ray spectra are presented for the EUV/X-ray source RE 1016-53. Multiwavelength observations of RE 1016-53 point out that it is a precataclysmic binary. Optical spectra exhibit the steep blue continuum and Balmer absorption typical of a hot white dwarf, but there are bright, narrow emission lines of H I, He I, and Ca II superimposed on this. The white dwarf component, with T (eff) = 55,800 +/- 1000 K and log g = 7.81 +/- 0.007, dominates the spectrum from the optical to the EUV/X-ray. An He II 4686 A absorption line suggests that the white dwarf is a hydrogen-helium (DAO) hybrid star. Four of the five precataclysmic binaries with white dwarfs with T(eff) greater than 40,000 K appear to be DAOs. A mass of 0.57 +/- 0.003 solar mass has been derived.

Tweedy, R. W.↗
NASA NTRS1994

The pre-cataclysmic binary EUVE 2013+400

New optical spectroscopy shows a 0.706 d orbital period for Extreme Ultraviolet Explorer (EUVE) 2013+400 and confirms its membership in a class of close binary systems emerging from common-envelope evolution. This binary, like the prototype Feige 24, consists of an extreme ultraviolet (EUV) emitting hot white dwarf and a late-type dwarf. Bergeron et al.'s (1994) optical spectroscopy and ultraviolet spectrophotometry indicate that the white dwarf is hot (T(sub eff) approximately equals 50 000 K) and therefore very young (t(sub age) less than or equal 5 x 10(exp 6) yr), and extreme ultraviolet photometry places EUVE 2013+400 along a neutral hydrogen column density in the interstellar medium of n(sub H) approximately equal to 10(exp 19)/sq cm. The white dwarf is a DAO type and we obtained two independent estimates of the helium abundance from EUV photometric measurements (log(y) approximately equal to -3.2) and from the He II lambda-4686 line profile (log(y) approximately equal to -2.8). The data possibly indicate a level of heterogeneity expected in the context of on-going chemical separation in the photospheric layers. The Balmer lines show narrow emission that varies with binary phase with the equivalent widths of the emission trailing the radial velocities by 1/4 cycle: this phasing shows that most of the emission arises on the EUV-illuminated face of the red dwarf. A spectrophotometric decomposition shows that the secondary's spectral type is near M3 and that it contributes about 15%-25% of the total light near 6500 A; the resulting H-alpha emission is twice as strong as in Feige 24, with an equivalent width of 37-61 A with respect to the red dwarf continuum. EUVE 2013+400 is an important addition to the class of close binary stars discovered in EUV all-sky surveys.

Thorstensen, John R.↗
NASA NTRS1994

The ultraviolet pulsations of the cataclysmic variable AE Aquarii as observed with the Hubble Space Telescope

We present the results of high time resolution UV spectroscopy and simultaneous high-speed UBVR photometry of AE Aqr. The UV spectra were obtained with the Faint Object Spectrograph aboard the Hubble Space Telescope (HST), and the photometry was carried out with the 82 sec telescope at McDonald Observatory. Our study focuses on the coherent 33 sceond oscillations, whose amplitude is found to be very large in the UV (40% of the mean quiescent level). The mean pulse profile has two broad unequal peaks spaced by half an oscillation cycle. The pulse profiles in the UV and optical bands appear quite similar in shape, with no discernible shifts. The orbital delay curve of the UV pulses establishes the white dwarf as their origin. The (UV+optical) spectrum of the pulsations is well described by a white dwarf atmosphere model with a temperature of about 26,000 K. We find no oscillations in the UV emission-line fluxes, nor in their velocities, down to a limit of 800 km/s. Based on the properties of the UV and optical pulsations we suggest that they originate in the X-ray heated magnetic polar caps of the white dwarf. Under this assumption we produce maximum entropy maps of the brightness distribution of the white dwarf surface. Using this model we are able to reproduce the observed mean pulse profile and interpret fluctuations in the oscillation amplitude as small fluctuations in the accretion rate. We find that the amplitudes and profiles of the pulses are not strongly affectd by the large aperiodic flares exhibited by the system. This suggests that the large flares are not related to the process of depositing material onto the white dwarf and argues against models that place their origin at the white dwarf magnetosphere.

Eracleous, Michael↗
NASA NTRS1993

Superhumps in cataclysmic variables: I. T. Leonis

We report photometry of the dwarf nova T Leonis during its 1993 supermaximum. The principle outburst lasted approximately 20 days, during which large-amplitude superhumps were consistently seen in the light curve. The mean period was 86.7 + or - 0.1 min, about 2.4% longer than the orbital period determined from radial-velocity measurements. Analysis of data obtained during the 1987 supermaximum implies that the superhump period decreased slowly, with dP/dt = - 6 x 10(exp -5), or dP/dm = -0.6 min. mag. These are typical values for SU Ursae Majoris-type dwarf novae. At the end of the outburst, the star suddenly brightened again to magnitude 13, from which it declined on a time scale of about 1 day and without superhumps. It is possible that this event was a normal outburst. This suggests that superoutbursts can trigger normal outbursts, and may explain the 'bump' frequently found in the light curves of SU UMa stars very late in a superoutburst.

Lemm, Kristi↗
NASA NTRS1992

Variability in the x-ray emission of H0538+608: An unusual AM Her-type cataclysmic variable

The x-ray emissions of AM Herculis-type object H0538+608 were observed using the ROSAT satellite. Evidence was found for a highly varying soft x-ray component with a much lower intensity than is typical for this class. The spectrum was well fit by a thermal bremsstrahlung model (exponential plus gaunt factor) of 35 +/- 5 KeV plus a 0.05 +/- 0.01 KeV blackbody component, with absorption by interstellar medium with a neutral hydrogen column density of log N(sub H) (atoms/sq cm) = 20.2. No obvious periodic variations were found. There was very little correlation between the hard and soft x-ray bands.

Catelli, Jennifer↗
NASA NTRS2001

ASCA Observations of the Dwarf Novae SS Cyg and VW Hyi And Observations of the Precessing Disk Cataclysmic Variable TV Col

The observations for both SS Cyg and VW Hyi were to be scheduled as Targets of Opportunity jointly with other satellites. The VW Hyi observation was obtained jointly with EUVE during a superoutburst. The XTE data were initially processed, revealing no detection. However, the XTE team improved the instrumental background model and distributed it in July 1998. A further improvement was made in August 1999. The improved models allow a better background subtraction, thereby detecting previously un-detected sources.

Schlegel, E.↗
NASA NTRS2002

The Disk Wind Model of the Broad Line Regions in Active Galactic Nuclei and Cataclysmic Variables

This is the final progress report for our Astrophysics Theory Program (NRA 97-OSS12) grant NAG5-7723. We have made considerable progress on incorporating photoionization calculations with a 2.5D hydrodynamical code to model disk winds in AGNs. Following up on our simultaneous broad band monitoring campaign of the type I Seyfert galaxy NGC 5548, we have investigated the constraints imposed on models of accretion in Seyfert galaxies by their optical, UV, and X-ray spectral energy distributions (SEDs). Using results from thermal Comptonization models that relate the physical properties of the hot inner accretion flow to the thermal reprocessing that occurs in the surrounding colder thin disk, we find that we can constrain the central black hole mass, accretion rate and size scale of the hot central flow. We have applied our model to observations of Seyfert galaxies NGC 3516, NGC 7469 and NGC 5548. Our mass and accretion rate estimates for these objects roughly agree with those found using other methods.

Begelman, Mitchell↗
NASA NTRS2004

FUSE Observations of the Bright, Eclipsing Nova-like Cataclysmic Variable, UX UMa (FUSE 2000)

This was a project to study the disk and wind of the eclipsing nova-like variable UX UMa, in order to better define the wind geometry of the system, including the nature of the transition region between the disk photosphere and the supersonic wind. We proposed to use phase resolved spectroscopy of the system, taking advantage of the fact that UX UMa is an eclipsing system, to isolate different regions of the wind and to use a Monte Carlo radiative transfer code to simulate the spectra through the eclipse.

Long, Knox↗
NASA NTRS2010

Computing Cosmic Cataclysms

The final merger of two black holes releases a tremendous amount of energy, more than the combined light from all the stars in the visible universe. This energy is emitted in the form of gravitational waves, and observing these sources with gravitational wave detectors requires that we know the pattern or fingerprint of the radiation emitted. Since black hole mergers take place in regions of extreme gravitational fields, we need to solve Einstein's equations of general relativity on a computer in order to calculate these wave patterns. For more than 30 years, scientists have tried to compute these wave patterns. However, their computer codes have been plagued by problems that caused them to crash. This situation has changed dramatically in the past few years, with a series of amazing breakthroughs. This talk will take you on this quest for these gravitational wave patterns, showing how a spacetime is constructed on a computer to build a simulation laboratory for binary black hole mergers. We will focus on the recent advances that are revealing these waveforms, and the dramatic new potential for discoveries that arises when these sources will be observed.

Centrella, Joan M.↗
NASA NTRS2012

V344 Lyrae: A Touchtone SU UMa Cataclysmic Variable in the Kepler Field

We report on the analysis of the Kepler short-cadence (SC) light curve of V344 Lyr obtained during 2009 June 20 through 2010 Mar 19 (Q2-Q4). The system is an SU UMa star showing dwarf nova outbursts and superoutbursts, and promises to be a touchstone for CV studies for the foreseeable future. The system displays both positive and negative super humps with periods of 2.20 and 2.06-hr, respectively, and we identify an orbital period of 2.11-hr. The positive super humps have a maximum amplitude of approximately 0.025-mag, the negative super humps a maximum amplitude of approximately 0.8 mag, and the orbital period at quiescence has an amplitude of approximately 0.025 mag. The quality of the Kepler data is such that we can test vigorously the models for accretion disk dynamics that have been emerging in the past several years. The SC data for V344 Lyr are consistent with the model that two physical sources yield positive superhumps: early in the superoutburst. the superhump signal is generated by viscous dissipation within the periodically flexing disk. but late in the superoutburst, the signal is generated as the accretion stream bright spot sweeps around the rim of the non-axisymmetric disk. The disk super humps are roughly anti-phased with the stream/late superhumps. The V344 Lyr data also reveal negative super humps arising from accretion onto a tilted disk precessing in the retrograde direction, and suggest that negative superhumps may appear during the decline of DN outbursts. The period of negative superhumps has a positive P(raised dot) in between outbursts.

Smale, Alan P.↗
NASA NTRS2012

The Vestal Cataclysm

The currently operating Dawn mission shows asteroid 4 Vesta to be an extensively cratered body, with craters in a variety of morphologies and preservation states The crater size-frequency distribution for Vesta, modeled using the lunar chronology and scaled to impact frequencies modeled for Vesta, shows that both the north and south pole areas are ancient in age [1]. We have in our meteorite collection products from 4 Vesta in the form of the HED (howardite, eucrite, diogenite) meteorites. The HED parent body globally differentiated and fully crystallized by approx.4.56 Ga; subsequently, the eucrites were brecciated and heated by large impacts into the parent body surface, reflected in their disturbance ages [2, 3]. Dawn images have also shown that Vesta is covered with a well-developed regolith that is spectrally similar to howardite meteorites [4, 5]. Howardites are polymict regolith breccias made up mostly of clasts of eucrites and diogenites, but which also contain clasts formed by impact into the regolith. Impact-melt clast ages from howardites extend our knowledge of the impact history of Vesta, expanding on eucrite disturbance ages and helping give absolute age context to the observed crater-counts on Vesta.

Cohen, Barbara A.↗
NASA NTRS2017

The Onset of the Cataclysm: In Situ Dating of a Nearside Basin Impact-Melt Sheet Or, There and Not Back Again

Impact-melt samples from Apollo Luna are 3.85-4.1 Ga, tied to Imbrium, Serenitatis, Crisium, Nectaris, plus other craters? May have been caused by destabilization of material in early solar system by dynamic forces such as gas drag and gravitational interactions Coincident with the oldest rocks on the Earth and later than the earliest isotopic signs of life on Earth. Earth was already a planet with oceans, plate tectonics, and single celled life What was happening on the Moon before 3.9 Ga affected the course of life on Earth, the structure of our Solar System, and the dynamics of extra solar planetary systems.

Cohen, Barbara A.↗