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2010MNRAS.404.2123F - Mon. Not. R. Astron. Soc., 404, 2123-2135 (2010/June-1)
Rocky planetesimals as the origin of metals in DZ stars.
FARIHI J., BARSTOW M.A., REDFIELD S., DUFOUR P. and HAMBLY N.C.
Abstract (from CDS):
Where detected, the hydrogen abundances for 37 DZA stars show little or no correlation with accreted calcium or spatial-kinematical distributions, though there is a general trend with cooling age. It is found that Eddington-type accretion of interstellar hydrogen can reproduce the observed hydrogen abundances, yet simultaneously fails to account for calcium. The calcium-to-hydrogen ratios for the DZA stars are dominated by supersolar values, as are the lower limits for the remaining 109 DZ stars. All together, these polluted white dwarfs currently contain 1020±2g of calcium in their convective envelopes, commensurate with the masses of calcium inferred for large asteroids.
A census of current Teff≲ 12000K, helium-rich stars from the Sloan Digital Sky Survey suggests the DZ and DC white dwarfs belong to the same stellar population, with similar basic atmospheric compositions, effective temperatures, spatial distributions and Galactic space velocities. Based on this result, pollution by the interstellar medium cannot simultaneously account for both the polluted and non-polluted subpopulations. Rather, it is probable that these white dwarfs are contaminated by circumstellar matter; the rocky remains of terrestrial planetary systems.
In this picture, two predictions emerge. First, at least 3.5 per cent of all white dwarfs harbour the remnants of terrestrial planetary systems; this is a concrete lower limit and the true fraction is almost certainly, and perhaps significantly, higher. Therefore, one can infer that at least 3.5 per cent of main-sequence A- and F-type stars build terrestrial planets. Secondly, the DZA stars are externally polluted by both metals and hydrogen, and hence constrain the frequency and mass of water rich, extrasolar planetesimals.
Abstract Copyright: © 2010 The Authors. Journal compilation © 2010 RAS
Journal keyword(s): minor planets, asteroids - circumstellar matter - stars: abundances - stars: chemically peculiar - planetary systems - white dwarfs
Simbad objects: 53
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