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Isotopic lithium abundances in five metal-poor disk stars *
P.E. Nissen 1,
D.L. Lambert 2,
F. Primas 3 and
V.V. Smith 4
Received 14 April 1999 / Accepted 28 May 1999
High resolution (), very high S/N spectra centered on the 6707.8 Å LiI line have been obtained with the ESO Coudé Echelle Spectrometer for five, metal-poor () disk stars in the turnoff region of the HR-diagram. The instrumental and stellar atmospheric line broadening have been determined from two unblended iron lines and used in a model atmosphere synthesis of the profile of the LiI line as a function of the lithium isotope ratio. This has led to a detection of 6Li in HD 68284 and HD 130551 with 6Li/7Li 0.05, whereas the other stars, HR 2883, HR 3578 and HR 8181, have 6Li/7Li close to zero.
By comparing -values and absolute magnitudes based on Hipparcos parallaxes with recent stellar evolutionary tracks, the masses of the stars have been derived. It is shown that the two stars with 6Li present have a significantly higher mass, , than the other three stars for which values between 0.85 and 1.0 are obtained.
The results are discussed in terms of models for the galactic evolution of the light elements and depletion of the lithium isotopes in stellar envelopes. It is shown that the measured 6Li abundances are in agreement with standard cosmic ray production of 6Li in the galactic disk and a moderate depletion (0.5 dex) in the stars. Recent models for the evolution of 6Li including fusion reactions and predicting a high lithium isotopic ratio, 6Li/7Li 0.3 at , require a high degree of 6Li depletion ( dex) to fit the observations. Furthermore, these models imply a 7Li abundance about 0.2 dex higher than observed for metal-poor disk stars.
Key words: stars: abundances stars: atmospheres stars: fundamental parameters stars: interiors ISM: cosmic rays
Send offprint requests to: P.E. Nissen
Online publication: July 16, 1999