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2003MNRAS.341..870B - Mon. Not. R. Astron. Soc., 341, 870-890 (2003/May-3)
Heavy-element abundance patterns in hot DA white dwarfs.
BARSTOW M.A., GOOD S.A., HOLBERG J.B., HUBENY I., BANNISTER N.P., BRUHWEILER F.C., BURLEIGH M.R. and NAPIWOTZKI R.
Abstract (from CDS):
We find that the presence or absence of heavy elements in the hot DA white dwarfs largely reflects what would be expected if radiative levitation is the supporting mechanism, although the measured abundances do not match the predicted values very well, as reported by other authors in the past. Almost all stars hotter than ∼50 000 K contain heavy elements. For most of these the spread in element abundances is quite narrow and similar to the abundances measured in G191-B2B. However, there is an unexplained dichotomy at lower temperatures with some stars having apparently pure H envelopes and others having detectable quantities of heavy elements. The heavy elements present in these cooler stars are often stratified, lying in the outermost layers of the envelope. A few strong temperature/evolutionary effects are seen in the abundance measurements. There is a decreasing Si abundance with temperature, the N abundance pattern splits into two groups at lower temperature and there is a sharp decline in Fe and Ni abundance to zero, below ∼50 000 K. When detected, the Fe and Ni abundances maintain an approximately constant ratio, close to the cosmic value of ∼20. For the hottest white dwarfs observed by STIS, the strongest determinant of abundance appears to be gravity.
Abstract Copyright: 2003 RAS
Journal keyword(s): stars: abundances - white dwarfs - ultraviolet: stars
Simbad objects: 25
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