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    Discovery of an Ultramassive Pulsating White Dwarf

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    2013_07_Hermes.pdf (652.0Kb)
    Date
    2013-07
    Author
    Hermes, J. J.
    Kepler, S. O.
    Castanheira, Barbara G.
    Gianninas, A.
    Winget, D. E.
    Montgomery, M. H.
    Brown, Warren R.
    Harrold, Samuel T.
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    Abstract
    We announce the discovery of the most massive pulsating hydrogen-atmosphere white dwarf (WD) ever discovered, GD 518. Model atmosphere fits to the optical spectrum of this star show it is a 12,030 +/- 210 K WD with a log g = 9.08 +/- 0.06, which corresponds to a mass of 1.20 +/- 0.03M(circle dot). Stellar evolution models indicate that the progenitor of such a high-mass WD endured a stable carbon-burning phase, producing an oxygen-neon-core WD. The discovery of pulsations in GD 518 thus offers the first opportunity to probe the interior of a WD with a possible oxygen-neon core. Such a massive WD should also be significantly crystallized at this temperature. The star exhibits multi-periodic luminosity variations at timescales ranging from roughly 425 to 595 s and amplitudes up to 0.7%, consistent in period and amplitude with the observed variability of typical ZZ Ceti stars, which exhibit non-radial g-mode pulsations driven by a hydrogen partial ionization zone. Successfully unraveling both the total mass and core composition of GD 518 provides a unique opportunity to investigate intermediate-mass stellar evolution, and can possibly place an upper limit to the mass of a carbon-oxygen-core WD, which in turn constrains Type Ia supernovae progenitor systems.
    Department
    Astronomy
    Subject
    stars: evolution
    stars: individual (gd 518)
    stars: oscillations
    stars: variables: general
    supernovae: general
    white dwarfs
    electron-capture supernovae
    digital sky survey
    stars
    evolution
    mass
    cores
    crystallization
    progenitors
    telescope
    astronomy & astrophysics
    URI
    http://hdl.handle.net/2152/43078
    Citation
    Hermes, James J., Souza Oliveira Kepler, Barbara G. Castanheira, Alexandros Gianninas, Donald Earl Winget, Michael Houston Montgomery, Warren R. Brown, and Samuel T. Harrold. "Discovery of an ultramassive pulsating white dwarf." The Astrophysical Journal Letters, Vol. 771, No. 1 (Jul., 2013): L2.
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    • facebook
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    • CONTACT US
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    Subscribe to our NewsletterGive to the Libraries

    © The University of Texas at Austin