Diffusion in PG 1159 stars

Unglaub, K.; Bues, I.

doi:10.1007/3-540-59157-5_186

Cited by 81 publications

(155 citation statements)

References 7 publications

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“…The way out of this conundrum is similar to that proposed in the context of the DAO and sdB stars (e.g., Fontaine & Chayer 1997;Unglaub & Bues 2000): a weak wind that pervades the atmosphere and envelope of the DO and DB stars and competes efficiently with the ongoing downward settling of carbon. The preliminary investigations of winds along the PG 1159/ DO/ DB cooling track ( Fontaine & Brassard 2005) are based on fully evolutionary models that include a wind for which the massloss rate decreases in a manner inversely proportional to the age and turns off by the time the DB star reaches 20,000 K. In the DB range, the mass-loss rate is of the order of $10 À13 M yr À1 , a value consistent with the rates discussed by Unglaub & Bues (2000).…”

Section: The Origin Of Carbonsupporting

confidence: 65%

“…The preliminary investigations of winds along the PG 1159/ DO/ DB cooling track ( Fontaine & Brassard 2005) are based on fully evolutionary models that include a wind for which the massloss rate decreases in a manner inversely proportional to the age and turns off by the time the DB star reaches 20,000 K. In the DB range, the mass-loss rate is of the order of $10 À13 M yr À1 , a value consistent with the rates discussed by Unglaub & Bues (2000). At this rate, the mass-loss process impedes the downward settling of carbon and leads to photospheric C/ He ratios in the DB range, log (C/ He) $ À7, substantially larger than predicted in windless models but consistent with the abundances we measure in DB stars ( Fig.…”

Section: The Origin Of Carbonmentioning

confidence: 71%

“…14). While this is quite speculative, given our ignorance of the wind-driving mechanism and the fact that mass loss might be expected to turn off much before the star reaches 20,000 K (e.g., Unglaub & Bues 2000), the idea appears interesting and deserves to be explored in more detail.…”

Section: The Origin Of Carbonmentioning

confidence: 99%

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FUSEObservations of DB White Dwarfs

Petitclerc¹,

Wesemaël²,

Kruk³

et al. 2005

ApJ

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We present a comprehensive analysis of the far-ultraviolet spectra of three DB white dwarfs secured with the FUSE observatory. Transitions associated with various carbon ions are detected in all three objects. Atmospheric parameters are first redetermined on the basis of an analysis of archival data available, and the abundance of carbon, together with upper limits on the abundances of 11 other heavy elements, is determined from the FUSE spectra. The log (C/ He) ratios cover the range between À5.5 and À6.0. The presence of carbon, now detected in five DB stars with effective temperatures above 20,000 K, cannot be accounted for easily by physical processes currently thought to operate in the envelopes of DB stars. We suggest that a weak stellar wind threading the outer stellar layers of DB stars might sufficiently disrupt the settling of carbon left over from the PG 1159 phase to account for the carbon seen in the ultraviolet spectra of these objects.

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Section: The Origin Of Carbonsupporting

confidence: 65%

Section: The Origin Of Carbonmentioning

confidence: 71%

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FUSEObservations of DB White Dwarfs

Petitclerc¹,

Wesemaël²,

Kruk³

et al. 2005

ApJ

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“…In particular, those PG 1159 stars resulting from a LTP -low-mass remnants are more prone to experience a LTP episode -are expected to evolve into DA white dwarfs (near the winds limits shown in Fig. 12 with solid dashed lines), thus avoiding the DO stage, as shown by Unglaub & Bues (2000). This is so because, in contrast to a VLTP event, in a LTP, H is not burned, but instead diluted to low surface abundances (Miller Bertolami & Althaus 2006).…”

Section: Results From Detailed Calculationsmentioning

confidence: 97%

Evolutionary and pulsational properties of white dwarf stars

Althaus

Córsico

Isern

et al. 2010

Astron Astrophys Rev

369

372

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White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. Since the coolest white dwarfs are very old objects, the present population of white dwarfs contains a wealth of information on the evolution of stars from birth to death, and on the star formation rate throughout the history of our Galaxy. Thus, the study of white dwarfs has potential applications to different fields of astrophysics. In particular, white dwarfs can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow to use these stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. Last but not least, since many white dwarf stars undergo pulsational instabilities, the study of their properties constitutes a powerful tool for applications beyond stellar astrophysics. In particular, white dwarfs can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants.These potential applications of white dwarfs have led to a renewed interest in the calculation of very detailed evolutionary and pulsational models for these stars. In this work, we review the essentials of the physics of white dwarf stars. We enumerate the reasons that make these stars excellent chronometers and we describe why white dwarfs provide tools for a wide variety of applications. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.

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“…Effective temperature and luminosity of KPD 0005+5106 are so high that a very weak radiation driven wind prevents gravitational settling of heavy elements in the atmosphere (Unglaub & Bues 2000). It therefore must have descended from the AGB as an object with an already helium-dominated surface.…”

Section: Discussionmentioning

confidence: 99%

Metal abundances in the hottest known DO white dwarf (KPD 0005+5106)

Wassermann

Werner

Rauch

et al. 2010

A&A

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We present the analysis of ultraviolet and optical spectra of KPD 0005+5106. Redetermination of the atmospheric parameters is necessary because the recent discovery of highly ionised metals (Ne viii, Ca x) indicates that the effective temperature is significantly higher than previously thought. Here we announce the discovery of lines from highly ionised silicon, sulphur, and iron (Si vii, S vii, Fe x) which were never found before in any stellar photosphere. Our analysis of these lines and those from helium and several other metals gives T eff = 200 000 ± 20 000 K, log g = 6.7 ± 0.3. Mass and luminosity follow from a comparison with evolutionary tracks: M = 0.64 M and log L/L = 3.7, so that, strictly speaking, the star is a helium-burning pre-white dwarf. The mass fractions of the metals in the helium-dominated atmosphere are in the range 0.7−4.3 solar. Hydrogen is not detectable and we derive an upper abundance limit of 0.034 solar. This abundance pattern is probably unaffected by gravitational settling and radiative levitation. Its origin lies in previous evolutionary stages. We discuss the link of KPD 0005+5106 to RCrB stars and the possibility that it results from a double-degenerate merger event.

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Diffusion in PG 1159 stars

Cited by 81 publications

References 7 publications

FUSEObservations of DB White Dwarfs

FUSEObservations of DB White Dwarfs

Evolutionary and pulsational properties of white dwarf stars

Metal abundances in the hottest known DO white dwarf (KPD 0005+5106)

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