The Impact of Accurate Distances on UV Spectroscopy of White Dwarfs and Cataclysmic Variables

It is well known that the evolution of white dwarfs (WDs) depends sensitively on the question whether they have “thin” or “thick” envelopes of H and He (see Wood 1995). Standard evolutionary caluclations (e.g. Paczynksi 1971) show that at the tip of the Asymptotic Giant Branch the envelope masses are tightly correlated with the mass of the hydrogen exhausted core (≈ total mass). Accordingly, the masses of hydrogen, MH, and helium, MHe, on top of the degenerate C/O interiors decrease by orders of magnitudes with increasing stellar mass. In contrast, many applications of WD calculations consider only single values of qH,He = log(MH,He/M∗) asuming either “thick” or “thin” envelopes.

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Expected Scientific Performance of the Three Spectrometers on the Extreme Ultraviolet Explorer

International Astronomical Union Colloquium ◽

10.1017/s0252921100012549 ◽

1990 ◽

Vol 115 ◽

pp. 335-338

Author(s):

J. V. Vallerga ◽

P. Jelinsky ◽

P. W. Vedder ◽

R. F. Malina

Keyword(s):

Wavelength Range ◽

Spectral Resolution ◽

Line Source ◽

White Dwarfs ◽

Extreme Ultraviolet ◽

Cataclysmic Variables ◽

Effective Area ◽

Light Sources ◽

Scientific Performance ◽

Astronomical Satellite

AbstractThe expected in-orbit performance of the three spectrometers included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite is presented. Recent calibrations of the gratings, mirrors and detectors using monochromatic and continuum EUV light sources allow the calculation of the spectral resolution and throughput of the instrument. An effective area range of 0.2 to 2.8 cm2 is achieved over the wavelength range 70-600Å with a peak spectral resolution λ/Δλ (FWHM) of ~ 360 assuming a spacecraft pointing knowledge of 10 arc seconds (FWHM). For a 40,000 sec observation, the average 3σ sensitivity to a monochromatic line source is 3 × 103 photons cm-2 sec-1. Simulated observations of known classes of EUV sources such as hot white dwarfs and cataclysmic variables are also presented.

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The Effective Temperature Distribution Function of Cataclysmic Variable White Dwarfs

International Astronomical Union Colloquium ◽

10.1017/s0252921100104622 ◽

1987 ◽

Vol 93 ◽

pp. 47-51

Author(s):

E.M. Sion

Keyword(s):

Distribution Function ◽

Temperature Distribution ◽

Orbital Period ◽

White Dwarf ◽

White Dwarfs ◽

Cataclysmic Variables ◽

Cataclysmic Variable ◽

Term Evolution ◽

Effective Temperatures

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.

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The evolution of ultra-massive white dwarfs

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833822 ◽

2019 ◽

Vol 625 ◽

pp. A87 ◽

Cited By ~ 22

Author(s):

María E. Camisassa ◽

Leandro G. Althaus ◽

Alejandro H. Córsico ◽

Francisco C. De Gerónimo ◽

Marcelo M. Miller Bertolami ◽

...

Keyword(s):

Phase Separation ◽

White Dwarf ◽

White Dwarfs ◽

Outer Boundary ◽

Asymptotic Giant Branch ◽

Type Ia ◽

Chemical Profiles ◽

Supernova Explosions ◽

Carbon Burning ◽

The Impact

Ultra-massive white dwarfs are powerful tools used to study various physical processes in the asymptotic giant branch (AGB), type Ia supernova explosions, and the theory of crystallization through white dwarf asteroseismology. Despite the interest in these white dwarfs, there are few evolutionary studies in the literature devoted to them. Here we present new ultra-massive white dwarf evolutionary sequences that constitute an improvement over previous ones. In these new sequences we take into account for the first time the process of phase separation expected during the crystallization stage of these white dwarfs by relying on the most up-to-date phase diagram of dense oxygen/neon mixtures. Realistic chemical profiles resulting from the full computation of progenitor evolution during the semidegenerate carbon burning along the super-AGB phase are also considered in our sequences. Outer boundary conditions for our evolving models are provided by detailed non-gray white dwarf model atmospheres for hydrogen and helium composition. We assessed the impact of all these improvements on the evolutionary properties of ultra-massive white dwarfs, providing updated evolutionary sequences for these stars. We conclude that crystallization is expected to affect the majority of the massive white dwarfs observed with effective temperatures below 40 000 K. Moreover, the calculation of the phase separation process induced by crystallization is necessary to accurately determine the cooling age and the mass-radius relation of massive white dwarfs. We also provide colors in the Gaia photometric bands for our H-rich white dwarf evolutionary sequences on the basis of new model atmospheres. Finally, these new white dwarf sequences provide a new theoretical frame to perform asteroseismological studies on the recently detected ultra-massive pulsating white dwarfs.

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Helium Abundance in the Photospheres of Hot Da White Dwarfs

International Astronomical Union Colloquium ◽

10.1017/s0252921100099553 ◽

1989 ◽

Vol 114 ◽

pp. 188-193 ◽

Cited By ~ 2

Author(s):

J. B. Holberg ◽

K. Kidder ◽

J. Liebert ◽

F. Wesemael

Keyword(s):

White Dwarfs ◽

Uv Spectroscopy ◽

Helium Abundance ◽

Apparent Contradiction ◽

X Ray ◽

Upper Limits

AbstractWe have used optical and UV spectroscopy to determine He abundances and upper limits to He abundances in the photospheres of a selected sample of very hot hydrogen-rich white dwarfs. He abundances in the range log(He/H) -3 to -1.5 are observed in several of these DAs and upper limits of -3 determined for the remainder. In apparent contradiction to the relatively large He abundances inferred from soft X-ray observations for the hot DA G191 B2B, we find no evidence of He in the optical and UV.

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Family links between Planetary Nebulae nuclei and cataclysmic variables, binary white dwarfs, R CrB stars, and SNe IA

Symposium - International Astronomical Union ◽

10.1017/s0074180900129869 ◽

1997 ◽

Vol 180 ◽

pp. 85-90

Author(s):

L.R. Yungelson ◽

A.V. Tutukov

Keyword(s):

White Dwarfs ◽

Cataclysmic Variables ◽

Planetary Nebulae ◽

Close Binaries ◽

Symbiotic Stars

We analyse the population of PNe and links between binary PNNi and stars which are in the later evolutionary stages. In a model which assumes that all stars are born in binaries, about 16% of PN result from ejection of common envelopes in close binaries, 85% of single PNNi are formed by merger of components of binaries. In the model, 5% of PNNi may be precataclysmic binaries, 5% may be precursors of symbiotic stars, 0.4% may be pre-SN Ia, 0.1% - precursors of hydrogen-deficient giants. About 0.1% of all PNe may be hydrogen-deficient.

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Physical Interpretation of Dwarf Nova Primary Effective Temperatures

International Astronomical Union Colloquium ◽

10.1017/s0252921100152431 ◽

2004 ◽

Vol 194 ◽

pp. 192-193

Author(s):

Dean M. Townsley ◽

Lars Bildsten

Keyword(s):

Gravitational Radiation ◽

Accretion Rate ◽

Thermal State ◽

Cataclysmic Variables ◽

Theoretical Work ◽

Dwarf Novae ◽

Radiation Losses ◽

Accretion Rates ◽

The Masses ◽

The Impact

AbstractWe have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10–11 – 10–8M⊙ yr–1. These accretion rates are most, appropriate to WDs in cataclysmic variables (CVs) of (Porb ≲ 7 hr), many of which accrete sporadically as Dwarf Novae. Over twenty Dwarf Novae have been observed in quiescence, when the accretion rate is low and the WD photosphere is detected and Teff measured. Comparing our theoretical work to these observations allows us to constrain the WD mass and the time averaged accretion rate, ⟨Ṁ⟩. If ⟨Ṁ⟩ is that given by gravitational radiation losses alone, then the WD masses are > 0.8 M⊙. An alternative conclusion is that the masses are closer to 0.6M⊙ and ⟨Ṁ⟩ is 3-4 times larger than that expected from gravitational radiation losses.

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Pulsating white dwarfs in cataclysmic variables: The marriage of ZZ Cet and dwarf nova

International Astronomical Union Colloquium ◽

10.1017/s0252921100010988 ◽

2004 ◽

Vol 193 ◽

pp. 382-386 ◽

Cited By ~ 3

Author(s):

Brian Warner ◽

Patrick A. Woudt

Keyword(s):

White Dwarf ◽

Large Amplitude ◽

White Dwarfs ◽

Cataclysmic Variables ◽

Sloan Digital Sky Survey ◽

Dwarf Novae ◽

Dwarf Nova ◽

Sky Survey

AbstractThere are now four dwarf novae known with white dwarf primaries that show large amplitude non-radial oscillations of the kind seen in ZZ Cet stars. We compare the properties of these stars and point out that by the end of the Sloan Digital Sky Survey more than 30 should be known.

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