A double white dwarf with a paradoxical origin?

Bours, Madelon C. P.; Marsh, T. R.; Gänsicke, B. T.; Tauris, T. M.; Istrate, Alina G.; Badenes, Carles; Dhillon, V. S.; Gal-Yam, A.; Hermes, J. J.; Kengkriangkrai, S.; Kilic, Mukremin; Koester, D.; Mullally, Fergal; Prasert, N.; Steeghs, D.; Thompson, Susan E.; Thorstensen, J. R.

doi:10.1093/mnras/stv889

Cited by 25 publications

(17 citation statements)

References 64 publications

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“…As discussed in Gianninas et al (2015) and Bours et al (2015), the models of Istrate et al (2014b; from here on I14) and Althaus et al (2013;A13) show a relatively large discrepancy in their cooling ages. Although the initial binary parameters, and to some extent the metallicities, are different in the two sets of models, the main difference is that the models of A13 include element diffusion, which has an important role in reducing the hydrogen envelope mass through flashes (cf.…”

Section: Comparison With Previous Workmentioning

confidence: 68%

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

Istrate

Marchant

Tauris

et al. 2016

A&A

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193

321

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A large number of extremely low-mass helium white dwarfs (ELM WDs) have been discovered in recent years. The majority of them are found in close binary systems suggesting they are formed either through a common-envelope phase or via stable mass transfer in a low-mass X-ray binary (LMXB) or a cataclysmic variable (CV) system. Here, we investigate the formation of these objects through the LMXB channel with emphasis on the proto-WD evolution in environments with different metallicities. We study for the first time the combined effects of rotational mixing and element diffusion (e.g. gravitational settling, thermal and chemical diffusion) on the evolution of proto-WDs and on the cooling properties of the resulting WDs. We present state-of-the-art binary stellar evolution models computed with MESA for metallicities of Z = 0.02, 0.01, 0.001 and 0.0002, producing WDs with masses between ∼0.16−0.45 M . Our results confirm that element diffusion plays a significant role in the evolution of proto-WDs that experience hydrogen shell flashes. The occurrence of these flashes produces a clear dichotomy in the cooling timescales of ELM WDs, which has important consequences e.g. for the age determination of binary millisecond pulsars. In addition, we confirm that the threshold mass at which this dichotomy occurs depends on metallicity. Rotational mixing is found to counteract the effect of gravitational settling in the surface layers of young, bloated ELM proto-WDs and therefore plays a key role in determining their surface chemical abundances, i.e. the observed presence of metals in their atmospheres. We predict that these proto-WDs have helium-rich envelopes through a significant part of their lifetime. This is of great importance as helium is a crucial ingredient in the driving of the κ-mechanism suggested for the newly observed ELM proto-WD pulsators. However, we find that the number of hydrogen shell flashes and, as a result, the hydrogen envelope mass at the beginning of the cooling track, are not influenced significantly by rotational mixing. In addition to being dependent on proto-WD mass and metallicity, the hydrogen envelope mass of the newly formed proto-WDs depends on whether or not the donor star experiences a temporary contraction when the H-burning shell crosses the hydrogen discontinuity left behind by the convective envelope. The hydrogen envelope at detachment, although small compared to the total mass of the WD, contains enough angular momentum such that the spin frequency of the resulting WD on the cooling track is well above the orbital frequency.

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Section: Comparison With Previous Workmentioning

confidence: 68%

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

Istrate

Marchant

Tauris

et al. 2016

A&A

Self Cite

193

321

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“…The evolution of our ultra-massive white dwarf sequences in the plane log(g) − T eff is depicted in Fig. 6 together with observational expectations taken from Mukadam et al (2004); Nitta et al (2016); Gianninas et al (2011); Kleinman et al (2013); Bours et al (2015); Kepler et al (2016); Curd et al (2017). In addition, isochrones of 0.1, 0.5, 1, 2, and 5 Gyr connecting the curves are shown.…”

Section: Evolutionary Resultsmentioning

confidence: 84%

The evolution of ultra-massive white dwarfs

Camisassa

Althaus

Córsico

et al. 2019

A&A

121

155

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Ultra-massive white dwarfs are powerful tools 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 up-dated 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 models 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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“…J2132 is clearly in the stable mass transfer range in Figure 3. Hence, there are now four confirmed double white dwarf progenitors of AM CVn; J0751, J1741 (Kilic et al 2014), J1257+5428 (Bours et al 2015), and J2132.…”

Section: Discussionmentioning

confidence: 91%

Massive double white dwarfs and the AM CVn birthrate

Kilic

Brown

Heinke

et al. 2016

Mon. Not. R. Astron. Soc.

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We present Chandra and Swift X-ray observations of four extremely low-mass (ELM) white dwarfs with massive companions. We place stringent limits on X-ray emission from all four systems, indicating that neutron star companions are extremely unlikely and that the companions are almost certainly white dwarfs. Given the observed orbital periods and radial velocity amplitudes, the total masses of these binaries are greater than 1.02 to 1.39 M ⊙ . The extreme mass ratios between the two components make it unlikely that these binary white dwarfs will merge and explode as Type Ia or underluminous supernovae. Instead, they will likely go through stable mass transfer through an accretion disk and turn into interacting AM CVn. Along with three previously known systems, we identify two of our targets, J0811 and J2132, as systems that will definitely undergo stable mass transfer. In addition, we use the binary white dwarf sample from the ELM Survey to constrain the inspiral rate of systems with extreme mass ratios. This rate, 1.7 × 10 −4 yr −1 , is consistent with the AM CVn space density estimated from the Sloan Digital Sky Survey. Hence, stable mass transfer double white dwarf progenitors can account for the entire AM CVn population in the Galaxy.

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A double white dwarf with a paradoxical origin?

Cited by 25 publications

References 64 publications

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing

The evolution of ultra-massive white dwarfs

Massive double white dwarfs and the AM CVn birthrate

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