Potential Evidence For Accretion Of Water-containing Asteroids Or A Callisto-analog Onto The White Dwarf GD 362

Details Potential Evidence For Accretion Of Water-containing Asteroids Or A Callisto-analog Onto The White Dwarf GD 362 Potential Evidence For Accretion Of Water-containing Asteroids Or A Callisto-analog Onto The White Dwarf GD 362

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21430604j&link_type=abstract

American Astronomical Society, AAS Meeting #214, #306.04; Bulletin of the American Astronomical Society, Vol. 41, p.729

Astronomy and Astrophysics

Astronomy

Scientific paper

GD 362 previously was found to be polluted by 15 elements heavier than helium with approximately
the abundance ratios relative to silicon of the bulk Earth/Moon system. The source of this contamination is the circumstellar dusty disk that orbits within the star's tidal radius and produces an
infrared excess. In view of two recent surveys of helium-rich dwarfs (Dufour et al. 2007, Voss et al. 2007) and by using a model for the depth of the convective envelope from Koester (2009), it seems that GD 362 possesses an anomalously large mass of
hydrogen. Possibly, there has been recent dredge-up of interior helium into an atmosphere that previously was hydrogen-dominated. Alternatively, there may have been interstellar or circumstellar accretion of hydrogen onto a helium-dominated atmosphere. Since GD 362 already is known to be undergoing circumstellar accretion of heavy elements, we discuss whether this star can have additionally accreted its atmospheric hydrogen from a parent body or parent bodies with internal ice. Here, we present models that are consistent with the elemental composition in the convective envelope, the infrared excess and the upper limit to the mass accretion rate from X-ray data acquired with XMM-Newton.
We suggest that the large mass of hydrogen in GD 362's convective envelope can be explained by substantial previous accretion onto the white dwarf either by a large swarm of water-rich asteroids or by an analog to Callisto.
This work has been partly supported by NSF and NASA.

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