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NASA NTRS1986

The space density of classical novae

A survey for Galactic plane ultraviolet-excess objects has been performed to obtain a statistically complete sample of cataclysmic variables from which to derive a space density. Six previously cataloged objects were recovered in the survey area of about 1000 sq deg, while one new nova was found, and two candidate cataclysmic variables were discovered. The resultant space densities of dwarf and novalike variables are consistent with previous determinations, while the nova space density is in good agreement with the recent determination of Patterson (1984), but is considerably lower than that of Bath and Shaviv (1978). However, if novae fade considerably between outbursts, as seems to be the case for the oldest recovered nova, CK Vulpeculae (1670), then the space density derived here may be greatly underestimated.

Downes, R. A.↗
NASA NTRS1986

First optical candidate for a recovered classical nova in a globular cluster - Nova 1938 in M14

U, B, V, R, and H-alpha CCD frames of the field of the nova which appeared in the globular cluster M14 in 1938 have been compared with the nova discovery images. On the basis of positional coincidence, brightness, and blue color, a candidate nova was identified and its right ascension and declination to within 1 arcsec each. Confirmation of the candidate and detailed study of the quiescent nova will probably require Hubble Space Telescope observations.

Shara, Michael M.↗
NASA NTRS1987

Numerical modelling of the classical nova outburst

A mechanism is described that promises to explain how nova outbursts take place on white dwarf of 1 solar mass or less and for accretion rates of 4 x 10 to the -10 solar mass/yr or greater.

Kutter, G. S.↗
NASA NTRS1988

Observations of classical novae in outburst

The IUE obtained ultraviolet data on novae in outburst. The characteristics of every one of the outbursts are different. Optical and infrared data on many of the same novae were also obtained. Three members of the carbon-oxygen class of novae are presented.

Starrfield, S.↗
NASA NTRS1990

Late stages in the evolution of classical novae

We have begun a study of the long term evolution of novae in outburst in order to determine the means by which they return in quiescence when nuclear burning has ended. This project involves both IUE and optical observations and theoretical predictions. Recently, in the initial observational part of this project, we have obtained IUE Short Wavelength Prime (SWP) spectra of GQ Mus 1983 and QU Vul 1984. Each spectrum was a 16 hour exposure using a combined US1 plus Vilspa shift. No novae have been studied in the UV for as long as QU Vul and GQ Mus and observations of their spectral evolution are providing unique data on the turn-off time scale. We have also obtained the spectra of old novae from the IUE archives in order to compare and contrast the existing spectra with those of GQ Mus and Qu Vul. The theoretical prediction is that a nova should be very hot just before turnoff but x ray observations from EXOSAT do not confirm this prediction.

Starrfield, S.↗
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

PW Vul: A classical nova with nearly solar abundances

Ultraviolet and optical spectrophotometric data are combined in order to determine the physical parameters in the expanding shell of Nova PW Vul 1984. Ultraviolet data obtained with the International Ultraviolet Explorer (IUE) satellite from August 2, 1984 (a few days after discovery) until it became too faint to study with the satellite is presented. The last IUE exposure was obtained in June 1988 but it was continually followed with ground based optical telescopes. A plot showing the variation of electron density and temperature as a function of time is presented. Analysis of the emission line intensities show that the abundances of this very slow nova are solar for helium, carbon, and oxygen while nitrogen is 50 times solar. The CLOUDY code of Ferland is used to model the emission line intensities and find good agreement with the observations. Plots representative of IUE and optical spectra are displayed.

Saizar, P.↗
NASA NTRS1990

Late stages in the evolution of classical novae

The long term evolution of novae in outburst is studied in order to determine the means by which they return to quiescence when nuclear burning has ended is described. The project involves both International Ultraviolet Explorer (IUE) and optical observations and theoretical predictions. In the initial observational part of this project, IUE SWP (Short Wavelength Prime) spectra of GQ Mus 1983 and QU Vul 1984 are obtained. Each spectrum was a 16 hour exposure using a combined US1 plus Vilspa shift. No novae were sudied in the UV for as long as QU Vul and GQ Mus and observations of their spectral evolution provides unique data on the turnoff time scale. The spectra of old novae from the IUE archives are used to compare the existing spectra with those of GQ Mus and QU Vul. The theoretical prediction is that a nova should be very hot just before turnoff but x ray observations from EXOSAT do not confirm this prediction.

Starrfield, Sumner G.↗
NASA NTRS1990

Near-infrared spectroscopy of classical novae in the coronal phase

Spectroscopic observations of V1819 Cyg, V827 Her, and V2214 Oph, obtained at 1-2.5 microns using a 32-channel InSb array detector at the Cassegrain focus of the 2.7-m telescope at McDonald Observatory during 1986-1989, are reported. The data are presented in extensive tables and graphs and characterized in detail, with a focus on the nature of the 'coronal' emission. The ratios of Br-gamma (2.167 microns) and forbidden Si VI (1.960 microns) are found to be consistent with coronal gas temperatures of about 10,000 K and with photoionization as the primary mechanism of origin for the coronal species. Severe constraints on theoretical models involving shock heating and collisional ionization are inferred.

Benjamin, Robert A.↗
NASA NTRS1992

Eclipse maps of the accretion disk in the classical nova V Persei

The surface brightness distribution in the accretion disk of V Per is reconstructed using a maximum entropy technique. The resulting brightness temperature gradient is much less steep than that from a standard steady state, optically thick disk for all reasonable mass accretion rates. A model including a rim which obscures part of the disk does not resolve this discrepancy. However, if the inner disk is disrupted out to about 0.15-0.25R sub L1 (for example by a magnetic field), the brightness temperature gradient can be very close to T sub b varies as R exp -3/4 (1-b(Rin/R)exp 1/2) law. The value of Rin needed to match this steady state distribution depends on the distance to the system, its size and brightness, and the rotation rate of the white dwarf.

Wood, Janet H.↗
NASA NTRS1993

Evolution of the symbiotic binary system AG Pegasi - The slowest classical nova eruption ever recorded

We present an analysis of new and existing photometric and spectroscopic observations of the ongoing eruption in the symbiotic star AG Pegasi, showing that this binary has evolved considerably since the turn of the century. Recent dramatic changes in both the UV continuum and the wind from the hot component allow a more detailed analysis than in previous papers. AG Peg is composed of a normal M3 giant and a hot, compact star embedded in a dense, ionized nebula. The hot component powers the activity observed in this system, including a dense wind and a photoionized region within the outer atmosphere of the red giant. The hot component contracted in radius at roughly constant luminosity from 1850 to 1985. Its bolometric luminosity declined by a factor of about 4 during the past 5 yr. Both the mass loss rate from the hot component and the emission activity decreased in step with the hot component's total luminosity, while photospheric radiation from the red giant companion remained essentially constant.

Kenyon, Scott J.↗
NASA NTRS1993

Typical examples of classical novae

Because of the very complicated individualistic behavior of each nova, we think it necessary to review the observations of a few well-observed individuals. We have selected a few objects of different speed classes, which have been extensively observed. They are: V1500 Cygni 1975, a very fast nova; V603 Aql 1918, fast nova; CP Pup 1942, fast nova; GK Per 1901, fast nova; V 1668 Cyg 1979, moderately fast nova; FH Ser 1970, slow nova; DQ Her 1934, slow nova; T Aur 1891, slow nova; RR Pic 1925, slow nova; and HR Del 1967, very slow nova.

Hack, Margherita↗
NASA NTRS2015

Suzaku Observation of the Classical Nova V2491 Cyg in Quiescence

We present Suzaku XIS observation of V2491 Cyg (Nova Cyg 2008 No. 2) obtained in quiescence, more than two years after the outburst. The nova was detected as a very luminous source in a wide spectral range from soft to hard X-rays. A very soft blackbody-like component peaking at 0.5 keV indicates that either we observe remaining, localized hydrogen burning on the surface of the white dwarf, or accretion onto a magnetized polar cap. In the second case, V2491 Cyg is a candidate "soft intermediate polar". We obtained the best fit for the X-ray spectra with several components: two of thermal plasma, a blackbody and a complex absorber. The later is typical of intermediate polars. The X-ray light-curve shows a modulation with an approximately 38 min period. The amplitude of this modulation is strongly energy dependent and reaches maximum in the 0.8-2.0 keV range. We discuss the origin of the X-ray emission and pulsations, and the likelihood of the intermediate polar scenario.

cataclysmic variables: general aEuro" nova: indivi↗
NASA NTRS2012

X-Ray Emission from an Asymmetric Blast Wave and a Massive White Dwarf in the Gamma Ray Emitting Nova V407 CYG

Classical nova events in symbiotic stars, although rare, offer a unique opportunity to probe the interaction between ejecta and a dense environment in stellar explosions. In this work, we use X-ray data obtained with Swift and Suzaku during the recent classical nova outburst in V407 Cyg to explore such an interaction. We find evidence of both equilibrium and non-equilibrium ionization plasmas at the time of peak X-ray brightness, indicating a strong asymmetry in the density of the emitting region. Comparing a simple model to the data, we find that the X-ray evolution is broadly consistent with nova ejecta driving a forward shock into the dense wind of the Mira companion. We detect a highly absorbed soft X-ray component in the spectrum during the first 50 days of the outburst that is consistent with supersoft emission from the nuclear burning white dwarf. The high temperature and short turn off time of this emission component, in addition to the observed breaks in the optical and UV lightcurves, indicate that the white dwarf in the binary is extremely massive. Finally, we explore the connections between the X-ray and GeV-ray evolution, and propose that the gamma ray turn-off is due to the stalling of the forward shock as the ejecta reach the red giant surface.

Nelson, Thomas↗