The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars

Althaus, Leandro Gabriel; Gerónimo, Francisco De; Córsico, Alejandro H.; Torres, Santiago; Garcı́a–Berro, E.

doi:10.1051/0004-6361/201629909

Cited by 22 publications

(24 citation statements)

References 68 publications

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“…LPCODE computes in detail the complete evolutionary stages leading to WD formation, allowing one to study the WD and pre-WD evolution in a consistent way with the expectations of the evolutionary history of progenitors. Details of LPCODE can be found in Althaus et al (2005Althaus et al ( , 2009Althaus et al ( , 2013Althaus et al ( , 2015Althaus et al ( , 2017 and references therein. Here, we mention only those physical ingredients which are relevant for our analysis of low-mass, He-core WD and pre-WD stars (see Althaus et al 2013, for details).…”

Section: Evolutionary Codementioning

confidence: 99%

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Calcaferro

Córsico

Althaus

2017

A&A

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Context. An increasing number of low-mass (M /M 0.45) and extremely low-mass (ELM, M /M 0.18−0.20) white-dwarf stars are being discovered in the field of the Milky Way. Some of these stars exhibit long-period g-mode pulsations, and are called ELMV variable stars. Also, some low-mass pre-white dwarf stars show short-period p-mode (and likely radial-mode) photometric variations, and are designated as pre-ELMV variable stars. The existence of these new classes of pulsating white dwarfs and pre-white dwarfs opens the prospect of exploring the binary formation channels of these low-mass white dwarfs through asteroseismology. Aims. We aim to present a theoretical assessment of the expected temporal rates of change of periods (Π) for such stars, based on fully evolutionary low-mass He-core white dwarf and pre-white dwarf models. Methods. Our analysis is based on a large set of adiabatic periods of radial and nonradial pulsation modes computed on a suite of low-mass He-core white dwarf and pre-white dwarf models with masses ranging from 0.1554 to 0.4352 M , which were derived by computing the non-conservative evolution of a binary system consisting of an initially 1 M ZAMS star and a 1.4 M neutron star companion. Results. We computed the secular rates of period change of radial ( = 0) and nonradial ( = 1, 2) g and p modes for stellar models representative of ELMV and pre-ELMV stars, as well as for stellar objects that are evolving just before the occurrence of CNO flashes at the early cooling branches. We find that the theoretically expected magnitude ofΠ of g modes for pre-ELMVs is by far larger than for ELMVs. In turn,Π of g modes for models evolving before the occurrence of CNO flashes are larger than the maximum values of the rates of period change predicted for pre-ELMV stars. Regarding p and radial modes, we find that the larger absolute values ofΠ correspond to pre-ELMV models. Conclusions. We conclude that any eventual measurement of a rate of period change for a given pulsating low-mass pre-white dwarf or white dwarf star could shed light about its evolutionary status. Also, in view of the systematic difficulties in the spectroscopic classification of stars of the ELM Survey, an eventual measurement ofΠ could help to confirm that a given pulsating star is an authentic low-mass white dwarf and not a star from another stellar population.

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Section: Evolutionary Codementioning

confidence: 99%

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Calcaferro

Córsico

Althaus

2017

A&A

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“…Many studies have been devoted to GC WDs (e.g., Renzini et al 1996;Zoccali et al 2001;Hansen & Liebert 2003;Moehler et al 2004;Bedin et al 2005;Strickler et al 2009;Richer et al 2013;García-Berro et al 2014;Torres et al 2015). So far, however, only Althaus et al (2017) have investigated in detail some effects of He enrichment on WD properties (see also, to a certain extent, Cassisi et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Evolution of long-lived globular cluster stars

Chantereau¹,

Charbonnel²,

Meynet³

2017

A&A

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Context. Globular clusters host stars with chemical peculiarities. The associated helium enrichment is expected to affect the evolution of stars, in general, and of low-mass stars, and in particular the progenitors of white dwarfs (WDs). Aims. We investigate the effects of different initial helium contents on the properties of WDs such as their masses, compositions, and the time since their formation. Methods. We used the grid of stellar models that we presented in the first papers of this series, which were computed for low-mass, low-metallicity stars with different helium content at [Fe/H] = −1.75 up to the end of the thermally pulsing asymptotic giant branch (TP-AGB) phase. We determined an initial-to-final mass relation as a function of the initial helium mass fraction, where the final mass is determined at the end of the TP-AGB phase. We couple the results with different possible distributions of the initial helium content for low-mass stars in NGC 6752 to predict the properties of WDs in this cluster. Results. In a globular cluster at a given age, the He enrichment implies lower initial masses for stars at a given phase. Thus it leads to a decrease of the masses of WDs reaching the cooling sequence. In addition the He enrichment increases the total mass and number of WDs and eventually allows the presence of He white dwarf from single progenitors. Conclusions. The low He enrichment determined in most globular clusters with different methods results in negligible effects on the white dwarf properties. However, in the few globular clusters that display a high He enrichment, this may significantly affect the characteristics of the WDs. In NGC 2808 and ω Centauri the high He enrichment even leads to the formation of He WDs from single He-rich progenitors. Therefore investigating the white dwarf mass domain in globular clusters with a high He enrichment would provide an additional indirect way to measure and constrain the He enrichment degree.

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“…We allowed some departure from the relation to account for a 500 K uncertainty in the white dwarf temperature. Note that the radii of very low metallicity ([Fe/H]<-3 dex) white dwarfs are 1-2 per cent larger than solar metallicity white dwarfs18, which is comparable to the departure allowed to account for the temperature uncertainty.…”

Section: Methodsmentioning

confidence: 85%

Accurate mass and radius determinations of a cool subdwarf in an eclipsing binary

et al. 2019

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Cool subdwarfs are metal-poor low-mass stars that formed during the early stages of the evolution of our Galaxy. Because they are relatively rare in the vicinity of the Sun, we know of few cool subdwarfs in the solar neighbourhood, and none with both the mass and the radius accurately determined. This hampers our understanding of stars at the low-mass end of the main-sequence. Here we report the discovery of SDSS J235524.29+044855.7 as an eclipsing binary containing a cool subdwarf star, with a white dwarf companion. From the light-curve and the radial-velocity curve of the binary we determine the mass and the radius of the cool subdwarf and we derive its effective temperature and luminosity by analysing its spectral energy distribution. Our results validate the theoretical mass-radius-effective temperature-luminosity relations for low-mass low-metallicity stars.

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The evolution of white dwarfs resulting from helium-enhanced, low-metallicity progenitor stars

Cited by 22 publications

References 68 publications

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Evolution of long-lived globular cluster stars

Accurate mass and radius determinations of a cool subdwarf in an eclipsing binary

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