Contents of: VI/111/./abstract/RWEINBER_DIBAPNE.abs

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 We propose to study newly formed dust around a class of
 ultrahot (ca. 100 000 K) pre-white dwarf stars. Such stars
 are, in general, of considerable importance for a detailed
 understanding of the phases of late stellar evolution. We
 intend to deal with a remarkable subgroup, "born-again"
 (Iben et al. 1983, ApJ 264, 605) stars, which are hot and
 hydrogen-deficient and have long defied a quantitative
 spectroscopic analysis due to their extremely high
 temperatures and peculiar chemical composition. In recent
 years, these PG 1159 stars, a part of which is surrounded
 by planetary nebulae, are considered as objects that
 suffered a late He shell flash and which are now retracing
 their post-AGB evolutionary track for the  second time. The
 most famous example for this "born-again" sample is A30, an
 old planetary nebula harbouring a central star which is
 surrounded by a tiny, complex, dust-rich  nebula. The dust
 is arranged in a disk-like structure, must have been formed
 quite recently - and is hot. The question of the highly
 interesting born-again scenario in context  with the origin,
 generation, location and, eventually, destruction of dust
 around such ultrahot stars will rest on two essential
 foundations: first, a suitable instrumentation for detailed
 observations of the infrared emission of the dust (which is,
 with exception of A30, usually small due to the small amount
 of dust) and, second, an accurate knowledge and understanding
 of the physical parameters of the stars that are responsible
 for the emitting material.
 ISO will provide excellent conditions for the first found-
 ation, whereas the sophisticated non-LTE model atmospheres by
 the Kiel group will be an outstanding means for the second.

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