The Pulsating White Dwarf Stars

Fontaine, G.; Brassard, P.

doi:10.1086/592788

Cited by 313 publications

(327 citation statements)

References 166 publications

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“…Of these two preliminary estimates, that of the effective temperature revealed itself somewhat suspect, given that KIC08626021 belongs to the shortest-period pulsators of all of the known V777 Her stars and, therefore, has to be among the hottest of the class according to the well known period-luminosity relation depicted, for example, in figure 25 of ref. 17. Hence, the true effective temperature of KIC08626021 has to be much higher than the estimate provided 8 , which is more characteristic of the red edge of the V777 Her instability strip 42 .…”

Section: Methodsmentioning

confidence: 88%

“…In the case of low-order, short-period g-modes such as those observed in KIC08626021, the periods are quite insensitive to the precise choice of the latter parameter (see, for example, figure 42 in ref. 17), so we fixed it to the 'flavour' ML2/α = 1.25, as calibrated through DB spectroscopy 33 .…”

Section: Methodsmentioning

confidence: 99%

“…This star shows an oscillation spectrum composed of non-radial g-modes, which are potentially sensitive to the deep interior of the star 17 . Using an analysis of 23 months of Kepler highprecision photo metric data 18 , we exploit the eight well secured independent modes, which have periods ranging from 143.2 s to 376.1 s (Fig.…”

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confidence: 99%

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A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf

Giammichele

Charpinet

Fontaine

et al. 2018

Nature

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125

177

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White-dwarf stars are the end product of stellar evolution for most stars in the Universe 1 . Their interiors bear the imprint of fundamental mechanisms that occur during stellar evolution 2,3 . Moreover, they are important chronometers for dating galactic stellar populations, and their mergers with other white dwarfs now appear to be responsible for producing the type Ia supernovae that are used as standard cosmological candles 4 . However, the internal structure of white-dwarf stars-in particular their oxygen content and the stratification of their cores-is still poorly known, because of remaining uncertainties in the physics involved in stellar modelling codes 5,6 . Here we report a measurement of the radial chemical stratification (of oxygen, carbon and helium) in the hydrogendeficient white-dwarf star KIC08626021 (J192904.6+444708), independently of stellar-evolution calculations. We use archival data 7,8 coupled with asteroseismic sounding techniques 9,10 to determine the internal constitution of this star. We find that the oxygen content and extent of its core exceed the predictions of existing models of stellar evolution. The central homogeneous core has a mass of 0.45 solar masses, and is composed of about 86 per cent oxygen by mass. These values are respectively 40 per cent and 15 per cent greater than those expected from typical white-dwarf models. These findings challenge present theories of stellar evolution and their constitutive physics, and open up an avenue for calibrating white-dwarf cosmochronology 11 .Hydrogen-deficient DB-type white dwarfs are dying stars that have effective temperatures ranging from about 12,000 K to upwards of 35,000 K (ref. 12). They have undergone a late final flash as postasymptotic-giant-branch (post-AGB) stars, which freed them from their thin remaining hydrogen envelope [13][14][15] . Their deeper chemical stratification-as in any typical white dwarf-is otherwise determined by the rate of the nuclear reaction 12 C(α ,γ ) 16 O, which synthesizes oxygen from the ashes of the core-helium-burning phase, by means of mixing processes associated with convection and rotation as well as the number of thermal pulses that occur in evolved AGB stars 16 . The descendant DB white dwarfs must bear the signature of such processes in their core, as well as the imprint of the still-ongoing settling of carbon and oxygen in the surrounding helium-rich envelope.KIC08626021 (GALEX J192904.6+ 444708) is the first pulsating DB white dwarf (also known as the V777 Her class of variable stars) to be moni tored extensively by the Kepler spacecraft for its pulsation properties 8 . This star shows an oscillation spectrum composed of non-radial g-modes, which are potentially sensitive to the deep interior of the star 17 . Using an analysis of 23 months of Kepler highprecision photo metric data 18 , we exploit the eight well secured independent modes, which have periods ranging from 143.2 s to 376.1 s (Fig. 1, Extended Data Table 1 and Methods). These relatively short pulsation periods are-accordin...

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Section: Methodsmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

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A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf

Giammichele

Charpinet

Fontaine

et al. 2018

Nature

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125

177

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“…In addition, they are used to place constraints on properties of elementary particles, such as axions (Isern et al 1992(Isern et al , 2008Córsico et al 2012a,b) and neutrinos (Winget et al 2004), or on alternative theories of gravitation (García-Berro et al 1995. These and other potential applications of white dwarfs require a detailed and precise knowledge of the main physical processes that control their evolution (see Fontaine & Brassard 2008;Kepler 2008, andAlthaus et al 2010a, for a review).…”

Section: Introductionmentioning

confidence: 99%

New evolutionary sequences for extremely low-mass white dwarfs

Althaus

Bertolami

Córsico

2013

A&A

256

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Context. The number of detected extremely low-mass (ELM) white dwarf stars has increased drastically in recent years, thanks to the results of many surveys. In addition, some of these stars have been found to exhibit pulsations, making them potential targets for asteroseismology. Aims. We provide a fine and homogeneous grid of evolutionary sequences for helium (He) core white dwarfs for the whole range of their expected masses (0.15 M * /M 0.45), including the mass range for ELM white dwarfs (M * /M 0.20). The grid is appropriate for mass and age determination of these stars, as well as for studying their adiatabic pulsational properties. Methods. White dwarf sequences have been computed by performing full evolutionary calculations that consider the main energy sources and processes of chemical abundance changes during white dwarf evolution. Realistic initial models for the evolving white dwarfs have been obtained by computing the nonconservative evolution of a binary system consisting of an initially 1 M ZAMS star and a 1.4 M neutron star for various initial orbital periods. To derive cooling ages and masses for He-core white dwarfs, we perform a least square fitting of the M(T eff , g) and Age(T eff , g) relations provided by our sequences by using a scheme that takes into account the time spent by models in different regions of the T eff − g plane. This is particularly useful when multiple solutions for cooling age and mass determinations are possible in the case of CNO-flashing sequences. We also explore in a preliminary way the adiabatic pulsational properties of models near the critical mass for the development of CNO flashes (∼0.2 M ). This is motivated by the discovery of pulsating white dwarfs with stellar masses near this threshold value. Results. We obtain reliable and homogeneous mass and cooling age determinations for 58 very low-mass white dwarfs, including three pulsating stars. Also, we find substantial differences in the period spacing distributions of g-modes for models with stellar masses near ∼0.2 M , which could be used as a seismic tool to distinguish stars that have undergone CNO flashes in their early cooling phase from those that have not. Finally, for an easy application of our results, we provide a reduced grid of values useful to obtain the masses and ages of He-core white dwarfs.

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“…Reviews of pulsating white dwarfs have been published by Winget & Kepler (2008), Fontaine & Brassard (2008), and Althaus et al (2010). Kepler et al (2005b) and Mukadam et al (2013) measured the rate of evolution of T eff 12 000 K white dwarfs using the rate of change of their pulsation periods, while Costa et al (2008a) measuredṖ for a T eff 140 000 K, PG 1159-035 pulsator.…”

Section: Compact Oscillatorsmentioning

confidence: 99%