Secular changes in the temperatures and radii of extreme helium stars

Details Secular changes in the temperatures and radii of extreme helium stars Secular changes in the temperatures and radii of extreme helium stars

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8603j&link_type=abstract

HST Proposal ID #8603

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Hst Proposal Id #8603 Hot Stars

Scientific paper

Extreme helium stars {EHEs} are luminous stellar remnants evolving rapidly to become white dwarfs. They represent an important stage in the evolution of at least some low-mass stars, and are closely related to the R Coronae Borealis variables. Models do not agree about their origin, nor about what fraction of normal stars pass through this phase, in which the stars have been completely stripped of their outer layers. The models do predict that EHEs are contracting and provide rate predictions and evolutionary lifetimes. First and second epoch IUE observations have shown that these contraction rates can be measured. We propose HST/STIS observations of 15 EHEs which, together with IUE data, will give a 20-year baseline of ultraviolet spectrophotometry. These observations will provide effective temperatures and angular radii with an internal accuracy for individual stars of 1% precision which cannot be achieved from optical or other diagnostics. From these measurements we will measure precise contraction rates for a larger sample of targets and obtain direct tests of the evolution models. Building on the IUE archive, the higher quality of HST data will provide a foundation dataset for establishing fundamental quantities {e.g. extinction} and for studying evolutionary changes in EHEs into the next century and beyond.

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