The pulsation index, effective temperature, and thickness of the hydrogen layer in the pulsating DA white dwarf G117-B15A

Robinson, E. L.; Mailloux, T. M.; Zhang, E.; Koester, D.; Stiening, R.; Bless, R. C.; Percival, J. W.; Taylor, Maryjane; Citters, G. W. van

doi:10.1086/175132

Cited by 106 publications

(143 citation statements)

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“…This is due to the small number of periods detected and/or the complex and changing structure of the pulsation spectrum characterizing DAVs. Robinson et al (1995) devised a method for mode identification that applies even in the cases in which there is a very reduced number of periods detected. The method is based on the effects of limb-darkening on the pulsation amplitudes.…”

Section: Mode Identificationmentioning

confidence: 99%

Evolutionary and pulsational properties of white dwarf stars

Althaus

Córsico

Isern

et al. 2010

Astron Astrophys Rev

370

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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Section: Mode Identificationmentioning

confidence: 99%

Evolutionary and pulsational properties of white dwarf stars

Althaus

Córsico

Isern

et al. 2010

Astron Astrophys Rev

370

372

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“…Follow-up Hubble Space Telescope (HST) ultraviolet observations confirmed the pulsation origin of this optical variability: the Fourier transform of the ultraviolet light curve shows periodic signals at 646, 376, and 237 s, but with amplitudes roughly 10 times higher than in the optical (Szkody et al 2002). Such a wavelength-dependent amplitude is expected because the ultraviolet lies in the exponential Wien tail of the spectral energy distribution, where the flux is more sensitive to changes in the temperature than at optical wavelengths (Robinson et al 1995). Additionally the amplitude depends also on the wavelength-dependent limb darkening.…”

Section: Introductionmentioning

confidence: 79%

“…The pulsations cause geometrical distortions in the white dwarf, leading to changes in the surface gravity, which are however, too small to be measured. The dominant effect of the pulsations is the appearance of hot and cool patterns on the white dwarf surface (Robinson et al 1995;Clemens, van Kerkwijk & Wu 2000). The three pulsations with well-defined periods identified during quiescence (2002 data), as well as the 293 s period found post-outburst (2010 and 2011 data), are generally believed to be due to non-radial white dwarf pulsations.…”

Section: 2010 and 2011 Observationsmentioning

confidence: 98%

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GW Librae: a unique laboratory for pulsations in an accreting white dwarf

Toloza

Gänsicke

Hermes

et al. 2016

Mon. Not. R. Astron. Soc.

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Non-radial pulsations have been identified in a number of accreting white dwarfs in cataclysmic variables. These stars offer insight into the excitation of pulsation modes in atmospheres with mixed compositions of hydrogen, helium, and metals, and the response of these modes to changes in the white dwarf temperature. Among all pulsating cataclysmic variable white dwarfs, GW Librae stands out by having a well-established observational record of three independent pulsation modes that disappeared when the white dwarf temperature rose dramatically following its 2007 accretion outburst. Our analysis of Hubble Space Telescope (HST) ultraviolet spectroscopy taken in 2002, 2010, and 2011, showed that pulsations produce variations in the white dwarf effective temperature as predicted by theory. Additionally in 2013 May, we obtained new HST/Cosmic Origin Spectrograph ultraviolet observations that displayed unexpected behaviour: besides showing variability at 275 s, which is close to the post-outburst pulsations detected with HST in 2010 and 2011, the white dwarf exhibits highamplitude variability on an 4.4 h time-scale. We demonstrate that this variability is produced by an increase of the temperature of a region on white dwarf covering up to 30 per cent of the visible white dwarf surface. We argue against a short-lived accretion episode as the explanation of such heating, and discuss this event in the context of non-radial pulsations on a rapidly rotating star.

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“…This puts the 3σ pulsation amplitude limit at 14 mmag. Note that the HST limit is from data at far-ultraviolet wavelengths, where pulsation amplitudes are generally much larger than at optical wavelengths (Robinson et al 1995), and may therefore still be the stronger limit even though the absolute value is somewhat higher than that from the ULTRASPEC data. Pulsation amplitudes tend to decline for white dwarfs with effective temperatures exceeding 11500 K (Mukadam et al 2006), and so it is possible that they are still present, but with amplitudes below the limits presented here.…”

Section: The Hot Massive White Dwarf and Possible Pulsationsmentioning

confidence: 98%

A double white dwarf with a paradoxical origin?

Bours¹,

Marsh²,

Gänsicke³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We present Hubble Space Telescope UV spectra of the 4.6 h period double white dwarf SDSS J125733.63+542850.5. Combined with Sloan Digital Sky Survey optical data, these reveal that the massive white dwarf (secondary) has an effective temperature T 2 = 13030 ± 70 ± 150 K and a surface gravity log g 2 = 8.73 ± 0.05 ± 0.05 (statistical and systematic uncertainties respectively), leading to a mass of M 2 = 1.06 M ⊙ . The temperature of the extremely low-mass white dwarf (primary) is substantially lower at T 1 = 6400 ± 37 ± 50 K, while its surface gravity is poorly constrained by the data. The relative flux contribution of the two white dwarfs across the spectrum provides a radius ratio of R 1 /R 2 ≃ 4.2, which, together with evolutionary models, allows us to calculate the cooling ages. The secondary massive white dwarf has a cooling age of ∼ 1 Gyr, while that of the primary low-mass white dwarf is likely to be much longer, possibly 5 Gyrs, depending on its mass and the strength of chemical diffusion. These results unexpectedly suggest that the low-mass white dwarf formed long before the massive white dwarf, a puzzling discovery which poses a paradox for binary evolution.

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The pulsation index, effective temperature, and thickness of the hydrogen layer in the pulsating DA white dwarf G117-B15A

Cited by 106 publications

References 0 publications

Evolutionary and pulsational properties of white dwarf stars

Evolutionary and pulsational properties of white dwarf stars

GW Librae: a unique laboratory for pulsations in an accreting white dwarf

A double white dwarf with a paradoxical origin?

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