Lithium 6104A in Population II stars

Abstract

We have obtained echelle spectroscopy of 14 Population II objects selected from those previously observed by Bonifacio & Molaro (1997). For one object, HD 140283, we obtained exquisite data with the High Dispersion Spectrograph on the Subaru Telescope, with S/N exceeding 1000 per 0.018A pixel. Li abundances have been determined by spectral synthesis from both the 6708A resonance line and also from 6104A subordinate feature. Firm detections of the weak line have been made in seven objects, and upper limits are reported for the remainder. Our 6708A abundances agree with those reported by Bonifacio & Molaro at the 99%-confidence level. Abundances from the 6104A line hint at a higher Li abundance than that determined from the resonance feature, but this evidence is mixed; the weakness of the 6104A line and the large number of upper limits make it difficult to draw firm conclusions. NLTE-corrections increase (rather than eliminate) the size of the (potential) discrepancy, and binarity appears unlikely to affect any abundance difference. The effect of multi-dimensional atmospheres on the line abundances was also considered, although it appears that use of 3-D (LTE) models could again act to increase the discrepancy, if one is indeed present.