Helium-rich EHB Stars in Globular Clusters: Extreme Horizontal Branch Stars and Related Objects (Guest Editor: P.F.L. Maxted)
Source: Astrophysics and Space Science, Volume 291, Number 3, 2004 , pp. 231-237(7)
Abstract:Recent UV observations of the most massive Galactic globular clusters show a significant population of hot stars below the zero-age HB (“blue hook” stars), which cannot be explained by canonical stellar evolution. Stars which suffer unusually large mass loss on the red giant branch and thus experience the helium-core flash while descending the white dwarf cooling curve could populate this region. They should show higher temperatures than the hottest canonical HB stars and their atmospheres should be helium-rich and probably C/N-rich. We have obtained spectra of blue hook stars in Cen and NGC 2808 to test this possibility. Our analysis shows that the blue hook stars in these clusters reach effective temperatures well beyond the hot end of the canonical EHB and have higher helium abundances than canonical EHB stars. These results support the hypothesis that the blue hook stars arise from stars which ignite helium on the white dwarf cooling curve.
Keywords: globular clusters
Document Type: Research Article
Affiliations: 1: Institut für Theoretische Physik und Astrophysik der Universität Kiel, Abteilung Astrophysik, 24098 Kiel, Germany., Email: email@example.com 2: NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, USA 3: Astronomisches Institut der Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
Publication date: January 1, 2004