Pulsations in Hydrogen Burning Low-Mass Helium White Dwarfs

Steinfadt, Justin D. R.; Bildsten, Lars; Arras, Phil

doi:10.1088/0004-637x/718/1/441

Cited by 49 publications

(80 citation statements)

References 58 publications

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“…This is based on the so-called convective driving mechanism originally proposed by Brickhill (1983Brickhill ( , 1990Brickhill ( , 1991aBrickhill ( , 1991b in his series of seminal papers to account for g-mode instabilities in ZZ Ceti white dwarfs. Steinfadt et al (2010) thus obtained a blue edge representing an extension of the ZZ Ceti instability strip into the low-mass regime in the log g-T eff plane (the circles in their Figure 3). Although the authors did not specify what convective efficiency they actually used in their calculations, it is likely that they employed the standard version of the mixing-length theory (denoted as ML1/α = 1.0 in white dwarf jargon) because they imported MESA subroutines (Paxton et al 2011), where this is the default option.…”

Section: Introductionmentioning

confidence: 92%

“…In this context, the search for pulsations in low-mass, He-core DA white dwarfs was spearheaded by Steinfadt et al (2010), who made a strong case for the importance and significance of finding such objects. These authors built several representative sequences of He-core DA stars with masses ranging from 0.15 M to 0.20 M and analyzed their pulsation characteristics, particularly the question of mode propagation.…”

Section: Introductionmentioning

confidence: 99%

“…In terms of mode stability, in the absence of full nonadiabatic calculations, Steinfadt et al (2010) estimated the location of the blue edge of a possible instability strip for low-mass DA white dwarfs using the semi-analytic criterion discussed by Brickhill (1991b) as applied to their stellar models. This criterion proposes a comparison of a "representative" period P-chosen as the one corresponding to the g-mode with = 1 and k = 1 in the models considered by Steinfadt et al-with the thermal timescale τ th at the base of the H convection zone of a given model according to the formula P 8πτ th .…”

Section: Introductionmentioning

confidence: 99%

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The Newly Discovered Pulsating Low-Mass White Dwarfs: An Extension of the Zz Ceti Instability Strip

Grootel

Fontaine

Brassard

et al. 2012

ApJ

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In light of the exciting discovery of g-mode pulsations in extremely low-mass, He-core DA white dwarfs, we report on the results of a detailed stability survey aimed at explaining the existence of these new pulsators as well as their location in the spectroscopic Hertzsprung-Russell diagram. To this aim, we calculated some 28 evolutionary sequences of DA models with various masses and chemical layering. These models are characterized by the so-called ML2/α = 1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We pulsated the models with the nonadiabatic code MAD, which incorporates a detailed treatment of time-dependent convection. On the other hand, given the failure of all nonadiabatic codes, including MAD, to account properly for the red edge of the strip, we resurrect the idea that the red edge is due to energy leakage through the atmosphere. We thus estimated the location of that edge by requiring that the thermal timescale in the driving region-located at the base of the H convection zone-be equal to the critical period beyond which = 1 g-modes cease to exist. Using this approach, we find that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip, including the low-gravity, low-temperature regime where the three new pulsators are found. We also account for the relatively long periods observed in these stars, and thus conclude that they are true ZZ Ceti stars, but with low masses.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Newly Discovered Pulsating Low-Mass White Dwarfs: An Extension of the Zz Ceti Instability Strip

Grootel

Fontaine

Brassard

et al. 2012

ApJ

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“…This new class of pulsating white dwarfs most probably belongs to a low-mass extension of the ZZ Ceti instability strip to much cooler effective temperatures. It is expected that the application of the tools of asteroseismology to these and other pulsating ELM white dwarfs found in the future will reveal details of their internal structure and evolutionary status; see Steinfadt (2010) and for the first exploration of the adiabatic properties of these objects.…”

Section: Introductionmentioning

confidence: 99%

New evolutionary sequences for extremely low-mass white dwarfs

Althaus

Bertolami

Córsico

2013

A&A

249

475

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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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“…The solid lines represent the fitted boundaries of the empirical ZZ Ceti instability strip as determined by Gianninas et al (2007) with the dashed line merely being the extension of the blue edge. The dash-dotted line represents the theoretical blue edge highlighted for very low mass He WDs by Steinfadt et al (2010a). We plot only objects we have observed.…”

Section: Introductionmentioning

confidence: 99%

A Search for Pulsations in Helium White Dwarfs

Steinfadt¹,

Bildsten²,

Kaplan³

et al. 2012

Publications of the Astronomical Society of the Pacific

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ABSTRACT. The recent plethora of sky surveys, especially the Sloan Digital Sky Survey, have discovered many low-mass (M < 0:45 M ⊙ ) white dwarfs that should have cores made of nearly pure helium. These WDs come in two varieties: those with masses 0:2 < M < 0:45 M ⊙ and H envelopes so thin that they rapidly cool and those with M < 0:2 M ⊙ (often called extremely low mass [ELM] WDs) that have thick enough H envelopes to sustain 10 9 yr of H burning. In both cases, these WDs evolve through the ZZ Ceti instability strip, T eff ≈ 9000-12; 000 K, where g-mode pulsations always occur in carbon/oxygen WDs. This expectation, plus theoretical work on the contrasts between C/O and He-core WDs, motivated our search for pulsations in 12 well-characterized helium WDs. We report here on our failure to find any pulsators among our sample. Though we have varying amplitude limits, it appears likely that the theoretical expectations regarding the onset of pulsations in these objects require closer consideration. We close by encouraging additional observations as new He WD samples become available, and we speculate on where theoretical work may be needed.

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Pulsations in Hydrogen Burning Low-Mass Helium White Dwarfs

Cited by 49 publications

References 58 publications

The Newly Discovered Pulsating Low-Mass White Dwarfs: An Extension of the Zz Ceti Instability Strip

The Newly Discovered Pulsating Low-Mass White Dwarfs: An Extension of the Zz Ceti Instability Strip

New evolutionary sequences for extremely low-mass white dwarfs

A Search for Pulsations in Helium White Dwarfs

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