Astron. Astrophys. 326, 731-735 (1997)

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Common envelope evolution and Li in V471 Tauri ^{* **}

Eduardo L. Martn ¹, Yakov Pavlenko ² and Rafael Rebolo <sup>1

1</sup> Instituto de Astrofísica de Canarias, E-38200 La Laguna, Spain
² The Main Observatory of the Academy of Sciences, Golosiiv Wood, Kyiv, Ukraine

Received 7 March 1997 / Accepted 30 April 1997

Abstract

We have observed the spectral regions around the LiI resonance 670.8 nm and subordinate 610.4 nm lines of V471 Tau. This is an eclipsing post common-envelope (CE) binary system. A revision of several independent measurements of the parallax and proper motion of V471 Tau allow us to argue that this system is indeed a Hyades cluster member by examining and rejecting earlier, flawed results. Using spectral synthesis and taking into account NLTE effects, we have derived a photospheric Li abundance of log N(Li)=2.35 0.25 for the K dwarf, which is a factor 100 higher than single Hyades members of the same mass. We argue that two mechanisms are responsible for this: a) Accretion of a substantial amount of Li-rich material onto the K dwarf during CE evolution inside the giant precursor of the white dwarf. Recently, a number of Li-rich giants have been observed and they appear to undergo large mass-loss. We speculate that CE evolution could actually explain the properties of these giants as well. b) Reduced Li depletion in the K dwarf due to sustained fast rotation in a short-period tidally-locked orbit. This process accounts for the preservation of Li after CE evolution has ceased.

Key words: stars: abundances - binaries: eclipsing - stars: evolution; interiors; individual: V471 Tau

* Based on data collected at the Isaac Newton telescope, operated by the Royal Greenwich Observatory in the Spanish Observatorio del Roque de los Muchachos.
** Corresponding author: E.L. Martín (ege@ll.iac.es)

SIMBAD Objects

Contents

• 1. Introduction
  • 1.1. Is V471 Tau a member of the Hyades cluster?
• 2. Spectroscopy
• 3. Chemical abundances in V471 Tau
• 4. Discussion
  • 4.1. Preservation of lithium
  • 4.2. CE evolution and Li enrichment
• 5. Summary
• Acknowledgements
• References

Note added in Proof: The parallax and proper motion of V471 Tau given in the Hipparcos output catalog confirm membership in the Hyades cluster

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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