Eduardo L. Martn 1,
Yakov Pavlenko 2 and
Rafael Rebolo 1
Received 7 March 1997 / Accepted 30 April 1997
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.
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