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Published February 2003 | Published + Accepted Version
Journal Article Open

Stellar Archaeology: A Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. III. The Lead (P[CLC]b[/CLC]) Star HE 0024−2523


We present a detailed abundance analysis, including spectral syntheses, of a very metal-poor ([Fe/H] ≃ -2.7) peculiar main-sequence star (HE 0024-2523) detected during the course of the Keck Pilot Program. Radial velocities of this star were obtained during four different observing runs over a time span of 1.1 yr and demonstrate that it is clearly a short-period spectroscopic binary. An orbital solution was obtained, and orbital parameters were determined with high precision. The rotational velocity was also measured (v_(rot) sin i = 9.7 ± 1.5 km s^(-1)); rotation appears likely to be synchronous with the orbit. The abundance analysis and spectral syntheses indicate that the object is a CH star characterized by extreme s-process enrichment, likely due to mass accretion from an evolved companion that has now probably become a white dwarf. The lead (Pb) abundance of (HE 0024-2523) is very high, the same as that of the recently discovered lead-rich, metal-poor star CS 29526-110, [Pb/Fe] = +3.3. The abundance ratio of the heavy to light s-elements, as characterized by Pb and Ba, [Pb/Ba] = +1.9, is the highest yet found for any metal-poor star and is about 0.7 dex higher than that of CS 29526-110. On the basis of the measured isotopic ratio of carbon (C^(12)/C^(13) ~ 6) we argue that the mass donor must have had an original mass of at least ~3 M⊙. The unusually short period of this CH star suggests that it underwent a past common-envelope phase with its evolved companion. Our results are compared with the latest available models for asymptotic giant branch yields and s-process nucleosynthesis. We also discuss the possible connection between HE 0024-2523, the lithium depletion of halo stars, and halo blue straggler formation.

Additional Information

© 2003 The American Astronomical Society. Received 2002 September 16; accepted 2002 October 31. Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and NASA. Based in part on observations collected at the European Southern Observatory, Paranal, Chile (ESO program 167.D-0173[A]). S. L., R. G, and E. C. acknowledge partial support from The MURST COFIN 2000. J. G. C and S. R. are grateful for partial support from the Fullham Award of the Dudley Observatory, and from grants AST 98-19614 and AST 02-05951 awarded by the National Science Foundation. N. C. acknowledges financial support through a Marie Curie Fellowship of the European Community program Improving Human Research Potential and the Socio-Economic Knowledge under contract HPMF-CT-2001-01437, and from Deutsche Forschungsgemeinschaft under grant Re 353/44-1. T. C. B. acknowledges partial support for this work from grants AST 00-98508 and AST 00-98549 awarded by the National Science Foundation. The authors are grateful to R. E. M. Griffin for supplying the ORBITSOLVER code. They also thank P. Bonifacio for performing part of the observations, and R. Gallino, F. D'Antona, P. Marigo and O. Straniero for useful discussions.

Attached Files

Published - Lucatello_2003_AJ_125_875.pdf

Accepted Version - 0211050.pdf


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