White Dwarf Temperature Research Articles

The Temperatures of White Dwarfs in Dwarf Novae

AbstractWe attempt to measure the temperature of all the quiescent dwarf novae that have been observed with IUE, by fitting the observed flux distribution of white dwarfs (WDs) with known temperatures. This approach gives results similar to those using much more sophisticated modelling, but allows us to investigate the relationship with system parameters and subclasses.

The ROSAT observations of classical novae

We observed a number of classical and recurrent novae in the Galaxy and the LMC with the ROSAT X-ray telescope and searched the archival data for other serendipitous observations. Preliminary results show that only 9 out of 37 observed objects were bright enough in X-rays to be detected with ROSAT, either in outburst or at quiescence.Three basic mechanisms can cause X-ray emission from classical or re-current novae. The first is hot hydrogen burning in a thin shell of the remnant envelope left on the white dwarf after the nova explosion. Hydrogen burning post-novae should be blackbody like emitters at nearly Eddington luminosity (as per the ‘supersoft’ X-ray sources). In our sample, only GQ Mus (Nova Mus 1983, see Ögelman et al. 1993; Shanley et al. 1995) and V1974 Cyg 1992 (Krautter et al. 1996) had these characteristics. Remarkably, among 10 LMC novae that had an outburst in the last 47 yr none was detected as a ‘supersoft’ X-ray source. The 3 σ upper limits for the black-body temperatures of the post-nova white dwarfs are mainly in the range 20… 30 eV. A post-nova can also emit X-rays because of shocks occurring in the ejected shell (e.g. O’Brien et al. 1994). Three out of four classical novae that were observed in outburst displayed a hard X-ray component in the ROSAT energy band, which might be due to a shocked shell. Finally, X-ray emission is expected from quiescent nearby novae because of accretion. Only four nearby accreting sources were detected; the ROSAT upper limits for the non-detected quiescent novae are Lx < 1031… 1032 ergs−1, assuming a thermal plasma at kT = a few keV.

VW Hyi: A Rapidly Cooling White Dwarf?

AbstractWe estimate the post-outburst cooling time-scale of the white dwarf in VW Hyi, using the available quiescent IUE spectra. The determination of the white-dwarf temperature close to the outburst is hampered because disc emission still contributes to the SWP flux.

Hopkins Ultraviolet Telescope Observations of U Geminorum Far from Outburst

The Hopkins Ultraviolet Telescope was used during the Astro-2 Space Shuttle mission to obtain a far-ultraviolet (820-1840 A) spectrum of the dwarf nova U Geminorum in its low state. At the time of the observation, U Gem had been at optical minimum for 185 days. The HUT spectrum is dominated by the white dwarf star, and shows (among other things) very strong, broad hydrogen Lyman absorption lines. A comparison with solar abundance white dwarf models indicates a temperature near ~30,000 K. Comparison to a similar spectrum obtained during the Astro-1 mission in 1990, only 10 days after U Gem had returned to the low state following a normal outburst, confirms that the average temperature of the white dwarf in U Gem drops substantially between outbursts. Furthermore, differences between the models and the data at the shortest wavelengths in both spectra support the hypothesis that the surface temperature is nonuniform and that a decrease in the relative importance of a hot region, possibly a belt, on the surface of the white dwarf causes the observed 30% decline in flux at 1450 A far from outburst.

RE 0044+09: A new K dwarf rapid rotator with a white dwarf companion

We report the discovery of a new K dwarf rapid rotator with a potential white dwarf companion. The white dwarf accounts for over 90% of the observed extreme ultraviolet flux detected from this system. Analysis of ROSAT Wide Field Camera (WFC) and IUE data both suggest a white dwarf temperature of approximately 28,700 K. Optical photometry and the IUE long wavelength prime (LWP) spectrum (with the white dwarf contribution removed) imply that the late-type star has a spectral type of K1-3 V, and a distance of 55 +/- 5 pc. Using this distance, the observed IUE SWP flux, and the best-fit temperature results in a white dwarf radius of 0.0088 solar radius. The estimated white dwarf mass is then approximately 0.91 solar mass; somewhat over-massive compared to field white dwarfs. Optical photometry of the K star reveals a 'spot' modulation period of approximately 10 hr (now observed over 3 yr). However, radial velocity observations have revealed no significant variations. Spectroscopic observations place a low limit on the lithium abundance, but do show rapid rotation with a v sin i of 90 +/- 10 km/s. The K star was detected as a radio source at 3.6 cm (on two occasions) and 6 cm by the Very Large Array (VLA). The most likely evolutionary scenario is that the K star and hot white dwarf from either a wide binary or common proper motion pair with an age of 0.1-0.1 Gyr-consistent with the evolutionary timescale of the white dwarf and the rapid rotation of the K star. However, from the proper motion of the K star, this system does not seem to be associated with any of the known young stellar groups.

The effect of the white dwarf temperature on nova outburst characteristics

The effect of the white dwarf temperature on nova outburst characteristics

RE1016 - 05: a white dwarf binary discovered with the ROSAT Wide Field Camera

We present new data on the extreme-ultraviolet source RE1016−05, discovered in the ROSAT Wide Field Camera All-Sky Survey. Spectroscopy of possible optical counterparts reveals an object with a composite DA white dwarf and M dwarf spectrum, only 19 arcsec distant from the Wide Field Camera (WFC) source coordinates. The spectra exhibit hydrogen Balmer line emission in the cores of wide Balmer absorption lines arising from the white dwarf, together with weaker He I line emission. There is evidence for variability in the optical emission-line flux on time-scales of hours, but no variation in EUV output is detected. We classify the cool companion in the range dM1-dM3, and determine the white dwarf temperature to be in the range 37 000-47 000 K

IUE spectra of the eclipsing binary NN Serpentis

Low-resolution SWP and LWP IUE spectra are used to fit the temperature and angular radius of the white dwarf in the detached eclipsing binary NN Ser. It is found that the redenning to the system has E(B-V) of 0.05 +/-0.05, the white dwarf temperature is 60,000 +/-10,000 K, and the age of the white dwarf is less than 10 exp 7. The shape of eclipse and the K-magnitude of the secondary star are used to constrain the inclination of the binary and the masses and radii of the two stars. The size of the secondary star relative to its Roche lobe and the age of the white dwarf indicate that mass transfer has not yet occurred and that the system is a precataclysmic variable rather than a cataclysmic variable which has entered the period gap. Fitting the observed magnitude of the sinusoidal modulation with a reprocessing model shows that only when i is approximately equal to 90 deg is the required temperature of the secondary star consistent with these results. For this solution the white dwarf temperature is also consistent with those obtained from the IUE spectra.

The Temperatures of White Dwarfs in Accreting Binaries

Through the use of accreting binary systems, it is possible to study the effects of the deposition of matter and energy on the surface of a white dwarf. The observed atmospheric properties of composition and temperature obtained from direct observation of the spectral lines and the continuum flux can be used to compare with those of single white dwarfs to understand the consequences of mass accretion on binary evolution.Cataclysmic variables provide one of the best targets for this type of study because a) the primaries are all white dwarfs b) the level and the timescale of the accretion cover a large range from the high rate, relatively steady novalike accretors to the dwarf novae systems which are modulated on short timescales in a quasi-periodic manner. Unfortunately, due to the mass transfer process, an accretion disk builds up to the point where its radiation overwhelms the white dwarf light in most cases. Thus, to study the effects on the stellar primary, systems must be found which have low mass transfer rates (generally the short orbital period systems (Patterson 1984)) and/or high inclinations (since most of the disk flux emerges perpendicular to the plane of the disk). The best identification of the white dwarf emerges from IUE spectra which show a broad Lyman α absorption profile (in contrast to the normal emission lines from a disk at quiescence). The shape of this profile provides a sensitive indicator of the temperature and gravity. In some cases, broad absorption lines are also evident in the optical Balmer lines, although the broad emission lines from the disk usually make these difficult to detect. The steeply falling flux distribution of a white dwarf throughout the optical region, combined with a flat disk distribution usually means that the white dwarf contributes a minor amount to the optical flux. However, in the ultraviolet, the rising energy distribution of the white dwarf easily dominates the falling energy distribution of a low accretion rate disk (Mateo and Szkody 1984). White dwarfs are generally acknowledged to be prominent in the dwarf novae U Gem (Panek and Holm 1984), VW Hyi (Mateo and Szkody 1984) and Z Cha (Marsh, Horne and Shipman 1987) and suggested in EK TrA and WZ Sge (Verbunt 1987). In addition, the white dwarf has been seen in some novalike systems which sporadically turn off their mass transfer, (resulting in the disappearance of most of the disk and the resulting appearance of the white dwarf). This has been the case in TT Ari (Shafter et al. 1985) and some limits have been determined for MV Lyr (Szkody and Downes 1982) and V794 Aql (Szkody, Downes and Mateo 1988). Several magnetic white dwarfs have also been seen when the mass transfer ceases in the AM Her systems (summarized in Szkody, Downes and Mateo 1988).

WHITE DWARFS IN CATACLYSMIC VARIABLES: LOW STATE IUE OBSERVATIONS OF V794 AQUILAE, MR SERPENTIS, AND AN URSAE MAJORIS

ABSTRACT The authors have obtained IUE low dispersion observations of one nova-like system (V794 Aql) and two AM Her systems (MR Ser and AN UMa) during low or intermediate low accretion rate states. 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.

The effective temperature distribution function of cataclysmic variable white dwarfs

With the recent detection of direct white dwarf photospheric radiation from certain cataclysmic variables in quiescent (low accretion) states, important implications and clues about the nature and long-term evolution of cataclysmic variables can emerge from an analysis of their physical properties. Detection of the underlying white dwarfs has led to a preliminary empirical CV white dwarf temperature distribution function and, in a few cases, the first detailed look at a freshly accreted white dwarf photosphere. The effective temperatures of CV white dwarfs plotted versus orbital period for each type of CV appears to reveal a tendency for the cooler white dwarf primaries to resisde in the shorter period systems. Possible implications are briefly discussed.

The Effective Temperature Distribution Function of Cataclysmic Variable White Dwarfs

AbstractWith the recent detection of direct white dwarf photospheric radiation from certain cataclysmic variables in quiescent (low accretion) states, important implications and clues about the nature and long-term evolution of cataclysmic variables can emerge from an analysis of their physical properties. Detection of the underlying white dwarfs has led to a preliminary empirical CV white dwarf temperature distribution function and, in a few cases, the first detailed look at a freshly accreted while dwarf photosphere. The effective temperatures of CV white dwarfs plotted versus orbital period for each type of CV appears to reveal a tendency for the cooler white dwarf primaries to reside in the shorter period systems. Possible implications are briefly discussed.

On the observed properties and long-term structure and evolution of white dwarfs in cataclysmic variables

An attempt is made to explain the observed surface temperatures and luminosities of cataclysmic variable white dwarfs based on the cooling physics and time-averaged structure of the white dwarf in response to accretion. The evolutionary changes in core temperature and core luminosity as an accreting white dwarf evolves quasi-statically are compared with the cooling evolution of a nonaccreting, one solar mass, pure C-12 core. Then, the evolutionary behavior of the white dwarf envelope in mass and temperature, in response to long-term accretion, is used to predict temperatures and luminosities of white dwarfs during quiescent intervals between nova outbursts. It is shown that the observed luminosities and effective temperatures of the bare white dwarfs detected in some cataclysmic variables are the expected intrinsic values associated with classical nova thermonuclear outburst cycles. Two alternate interpretations of their observed surface temperatures and luminosities are assessed.

Hot Subluminous Stars

Extensive mass loss is observed for hot subluminous stars, through P Cygni lines in the ultraviolet. This persists in some sub-dwarf 0 stars, but is generally not observed in white dwarfs. The ultraviolet provides determination of effective temperatures. Among nine sdO’s, the maximum temperature reported is definitely below 60, 000 K; an object at 100, 000 K would be distinguishable. The sdO’s show a wide variety of line strengths, notably in N V, C IV and Si TV, as well as He II. One halo sdB is reported as rich in peculiar elements; it shows anomalous N V for its temperature. The comparison of effective temperatures of white dwarfs observed from space and from the ground gives excellent agreement. The hottest white dwarfs are near 60, 000 K, although one (helium-rich) reaches 80, 000 K. Another helium-rich close binary probably has an accretion disk; it is the only white dwarf to show the expanding shell of N V, C IV, Si IV characteristic of some subdwarfs. Two magnetic white dwarfs have been observed; one has strong unidentifiable features and the smallest known radius.

Discovery of a nonsolar extreme-ultraviolet source

view Abstract Citations (97) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a nonsolar extreme-ultraviolet source. Lampton, M. ; Margon, B. ; Paresce, F. ; Stern, R. ; Bowyer, S. Abstract Results are reported for observations of EUV emission from an extrasolar object which were made with a grazing-incidence telescope during the Apollo-Soyuz mission. The total energy flux in the spectral band between 170 and 620 A is estimated to be approximately 4 by 10 to the -9th power erg/sq cm per sec. It is shown that the data support the identification of the EUV object with the ultrasoft X-ray source in Coma Berenices. The source of both emissions is suggested to be the hot white dwarf HZ 43, located at right ascension 13 hr 43 min and declination +29 deg 22 min (1950). The temperature of HZ 43 is estimated as 110,000 K, giving it the highest temperature of any known white dwarf. Publication: The Astrophysical Journal Pub Date: January 1976 DOI: 10.1086/182022 Bibcode: 1976ApJ...203L..71L Keywords: Far Ultraviolet Radiation; Radiation Sources; Stellar Spectrophotometry; X Ray Sources; Apollo Soyuz Test Project; Apollo Telescope Mount; Black Body Radiation; Extraterrestrial Radiation; Grazing Incidence Telescopes; Spectral Energy Distribution; White Dwarf Stars; Astronomy full text sources ADS | data products SIMBAD (2) Related Materials (1) Part 2: 1976ApJ...209..525M

Effective Temperatures of White Dwarfs

Of all the fields of stellar astronomy, the study of white dwarfs has been most influenced by work done on proper motions. From proper motion studies, particularly by Luyten and Giclas in recent years, many white dwarf candidates have been found. These candidates have been studied intensively, particularly by Greenstein who has obtained spectra and Eggen who has measured magnitude and colors. As a result, many new white dwarfs have been discovered, and we now have many examples of most types of white dwarfs. It is, therefore, possible to study each group separately and to find relationships between the various types of white dwarfs.