A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes

Garcı́a–Berro, E.; Torres, Santiago; Althaus, Leandro Gabriel; Renedo, Isabel; Lorén–Aguilar, Pablo; Córsico, A. H.; Rohrmann, R. D.; Salaris, Maurizio; Isern, J.

doi:10.1038/nature09045

Cited by 239 publications

(233 citation statements)

References 22 publications

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“…This code has recently been used to produce very accurate white dwarf models (see García-Berro et al 2010;Althaus et al 2010b;Renedo et al 2010;Miller Bertolami et al 2011a,b, and references therein). The code has also been used to study the formation of subdwarf stars from the post-red giant branch (RGB) hot-flasher scenario (Miller Bertolami et al 2008), as well as the role of thermohaline mixing for the surface composition of low-mass giant stars (Wachlin et al 2011).…”

Section: Numerical Toolsmentioning

confidence: 99%

“…White dwarf stars are routinely used to constrain the age and past history of the Galactic populations, including the solar neighborhood and open and globular clusters (Von Hippel & Gilmore 2000;Hansen et al 2007;Winget et al 2009;García-Berro et al 2010;Bono et al 2013, and references therein). 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.…”

Section: Introductionmentioning

confidence: 99%

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New evolutionary sequences for extremely low-mass white dwarfs

Althaus

Bertolami

Córsico

2013

A&A

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256

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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Section: Numerical Toolsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New evolutionary sequences for extremely low-mass white dwarfs

Althaus

Bertolami

Córsico

2013

A&A

Self Cite

256

475

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“…This discrepancy has led to a detailed reevaluation of the effect of diffusion of 22 Ne in the CO core before crystallization sets in (e.g., Bravo et al 1992, Deloye & Bildsten 2002. As shown by García-Berro et al (2010 with full evolutionary calculations, at the old age and high metallicity of this cluster (about twice solar), the extra-energy contributed by Ne-diffusion in the liquid phase slows down substantially the cooling of the models and can bring into agreement WD, TO and eclipsing binary ages.…”

Section: Introductionmentioning

confidence: 99%

Hubble Space Telescope observations of the Kepler-field cluster NGC 6819 – I. The bottom of the white dwarf cooling sequence★

Bedin

Salaris

Anderson

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We use Hubble Space Telescope (HST ) to reach the end of the white dwarf (WD) cooling sequence (CS) in the solar-metallicity open cluster NGC 6819. Our photometry and completeness tests show a sharp drop in the number of WDs along the CS at magnitudes fainter than m F606W = 26.050 ± 0.075. This implies an age of 2.25 ± 0.20 Gyr, consistent with the age of 2.25 ± 0.30 Gyr obtained from fits to the main-sequence turn-off. The use of different WD cooling models and initial-final-mass relations have a minor impact the WD age estimate, at the level of ∼0.1 Gyr. As an important by-product of this investigation we also release, in electronic format, both the catalogue of all the detected sources and the atlases of the region (in two filters). Indeed, this patch of sky studied by HST (of size ∼70 arcmin 2 ) is entirely within the main Kepler-mission field, so the high-resolution images and deep catalogues will be particularly useful.

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“…Matsuura et al 2009;McDonald et al E-mail: r.raddi@warwick.ac.uk 2011); (ii) infer the mass-to-light ratio of galaxies (e.g. Maraston 1998; Kotulla et al 2009); (iii) date old stellar populations in open (García-Berro et al 2010) and globular clusters (Richer et al 1997;Hansen et al 2004), or in the different constituents of the Milky Way, i.e. the disc (Winget et al 1987;Oswalt et al 1996), the bulge (Calamida et al 2014;Gesicki et al 2014), and the halo (Kalirai 2012).…”

Section: Introductionmentioning

confidence: 99%

A search for white dwarfs in the Galactic plane: the field and the open cluster population

Raddi¹,

Catalán²,

Gänsicke³

et al. 2016

Mon. Not. R. Astron. Soc.

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We investigated the prospects for systematic searches of white dwarfs at low Galactic latitudes, using the VLT Survey Telescope H α Photometric Survey of the Galactic plane and Bulge (VPHAS+). We targeted 17 white dwarf candidates along sightlines of known open clusters, aiming to identify potential cluster members. We confirmed all the 17 white dwarf candidates from blue/optical spectroscopy, and we suggest five of them to be likely cluster members. We estimated progenitor ages and masses for the candidate cluster members, and compare our findings to those for other cluster white dwarfs. A white dwarf in NGC 3532 is the most massive known cluster member (1.13 M ), likely with an oxygen-neon core, for which we estimate an 8.8 +1.2 −4.3 M progenitor, close to the mass-divide between white dwarf and neutron star progenitors. A cluster member in Ruprecht 131 is a magnetic white dwarf, whose progenitor mass exceeded 2-3 M . We stress that wider searches, and improved cluster distances and ages derived from data of the ESA Gaia mission, will advance the understanding of the mass-loss processes for low-to intermediate-mass stars.

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A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes

Cited by 239 publications

References 22 publications

New evolutionary sequences for extremely low-mass white dwarfs

New evolutionary sequences for extremely low-mass white dwarfs

Hubble Space Telescope observations of the Kepler-field cluster NGC 6819 – I. The bottom of the white dwarf cooling sequence★

A search for white dwarfs in the Galactic plane: the field and the open cluster population

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