THE CORE COMPOSITION OF A WHITE DWARF IN A CLOSE DOUBLE-DEGENERATE SYSTEM

We report the identification of the double-degenerate system NLTT 16249 that comprises a normal, hydrogen-rich (DA) white dwarf and a peculiar, carbon-polluted white dwarf (DQ) showing photospheric traces of nitrogen. We disentangled the observed spectra and constrained the properties of both stella...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2012-01, Vol.745 (1), p.1-5
Main Authors: Vennes, S, Kawka, A
Format: Article
Language:English
Subjects:
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Asymptotic properties
ASYMPTOTIC SOLUTIONS
CARBON
Combustion
ELEMENT ABUNDANCE
Envelopes
Estimates
HELIUM
HELIUM BURNING
HYDROGEN
MASS
NITROGEN
NITROGEN 14
Orbitals
PHOTOSPHERE
Progenitors (astrophysics)
WHITE DWARF STARS
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Summary:We report the identification of the double-degenerate system NLTT 16249 that comprises a normal, hydrogen-rich (DA) white dwarf and a peculiar, carbon-polluted white dwarf (DQ) showing photospheric traces of nitrogen. We disentangled the observed spectra and constrained the properties of both stellar components. In the evolutionary scenario commonly applied to the sequence of DQ white dwarfs, both carbon and nitrogen would be dredged up from the core. The C/N abundance ratio ([asymptotically =]50) in the atmosphere of this unique DQ white dwarf suggests the presence of unprocessed material ( super(14)N) in the core or in the envelope. Helium burning in the DQ progenitor may have terminated early on the red giant branch after a mass-ejection event leaving unprocessed material in the core, although current mass estimates do not favor the presence of a low-mass helium core. Alternatively, some nitrogen in the envelope may have survived an abridged helium-core burning phase prior to climbing the asymptotic giant branch. Based on available data, we estimate a relatively short orbital period (P [
ISSN:2041-8205
2041-8213
DOI:10.1088/2041-8205/745/1/L12