On the surface composition of cool, hydrogen-line white dwarfs - Discovery of helium in the atmospheres of cool DA stars and evidence for convective mixing

Journal Article · Thu Mar 01 04:00:00 EST 1990 · Astrophysical Journal; (USA)

DOI:https://doi.org/10.1086/185670· OSTI ID:7135443

Bergeron, P; Wesemael, F; Fontaine, G; Liebert, J ^[1]

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1. Montreal Universite, Montreal (Canada) Steward Observatory, Tucson, AZ (USA)

A determination of the He abundance in 37 cool DA white dwarfs is presented. A spectroscopic analysis of the high Balmer lines reveals that the atmospheres of most objects below Te of about 11,500 K are contaminated by significant amounts of He, with abundances sometimes as high as N(He)/N(H) of about 20. This result is interpreted as the result of convective mixing between the thin superficial H layer with the more massive underlying He envelope. The lack of H-rich objects in the sample in the range Te = 7500-11,500 K indicates that most DA white-dwarfs mix near Te of about 11,500 K, a result which is consistent with the location of the red edge of the ZZ Ceti instability strip. A definite trend for cooler objects to have lower He abundances is also observed. 37 refs.

• OSTI ID: 7135443
• Journal Information: Astrophysical Journal; (USA), Journal Name: Astrophysical Journal; (USA) Vol. 351; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
ATMOSPHERES
BALMER LINES
CHEMICAL COMPOSITION
CONVECTION
DWARF STARS
ELEMENT ABUNDANCE
ELEMENTS
ENERGY TRANSFER
FLUIDS
GASES
HEAT TRANSFER
HELIUM
MASS TRANSFER
MIXING
NONMETALS
RARE GASES
STARS
STELLAR ATMOSPHERES
WHITE DWARF STARS