Lithium abundances from the 6104 Å line in cool Pleiades stars

Abstract

Abstract. Lithium abundances determined by spectral synthesis from both the 6708 Å resonance line and the 6104 Å subordinate line are reported for 11 Pleiades late-G and early-K stars observed at the William Herschel Telescope. Firm detections of the weak subordinate line are found for four objects, marginal detections for four, and upper limits for the remaining three stars. Some of these spectra were previously analysed by Russell (1996), where he reported that abundances derived from the 6104 Å line were systematically higher than those obtained from the 6708 Å line by 0.2-0.7 dex. He also reported a reduced spread in the 6104 Å line abundances compared with those determined from the 6708 Å feature. Using spectral synthesis we have re-analysed Russell's data, along with our own. Our results do not entirely support Russell's conclusions. We report a ∼0.7 dex scatter in the abundances from 6708 Å and a scatter at least as large from the 6104 Å line. We find that this is partly explained by our inclusion of a nearby Fe  line and careful modelling of damping wings in the strong metal lines close to the 6104 Å feature; neglect of these leads to overestimates of the Li abundance which are most severe in those objects with the weakest 6104 Å lines, thus reducing the abundance scatter. We find a reasonable correlation between the 6104 Å and 6708 Å Li abundances, although four stars have 6104 Å-determined abundances which are significantly larger than the 6708 Å-determined values by up to 0.5 dex, suggesting problems with the homogeneous, 1-dimensional atmospheres being used. We show that these discrepancies can be explained, although probably not uniquely, by the presence of star spots with plausible coverage fractions. The addition of spots does not significantly reduce the apparent scatter in Li abundances, leaving open the possibility that at least some of the spread is caused by real star-to-star differences in pre-main sequence Li depletion.

Lithium 6104 Å in Population II stars

“…In a related paper (Ford et al 2002) we found evidence that 6104 gave higher Li abundances than 6708 for some young Pleiades G/K dwarfs, whilst for others there seems to be reasonable agreement. This is very similar to the situation we find here for Pop.…”

“…Recent work by Kurucz (1995), Carlsson et al (1994), Stuik et al (1997), Uitenbroek (1998) and Asplund et al (1999) has suggested that this line might be unrepresentative of the actual Li abundance within the stars, due to omissions in our understanding and modelling of stellar atmospheres. Recent works on halo stars (Bonifacio & Molaro 1998, hereafter BM98 -and next subsection) and young cluster stars (Soderblom et al 1993a;Russell 1996;Ford et al 2002) have used the weak (excitation potential = 1.8 eV) Li  subordinate line at 6104 Å in addition to the 6708 Å line (hereafter 6708 and 6104 are taken to mean "the Li  line at 6708 Å" and "the Li  line at 6104 Å" respectively), to attempt to determine Li abundances. This paper builds on those previous studies.…”

Chemical composition of A and F dwarfs members of the Pleiades open cluster

“…Stars studied Chemical elements Pilachowski et al (1987) 18 A, F, G Li Burkhart & Coupry (1997) 8 A-Am Li, Al, Si, S, Fe, Ni, Eu Hui- Bon-Hoa & Alecian (1998) 9 A-Am Mg, Ca, Sc, Cr, Fe, Ni 1 2F F e 1 2F C Boesgaard et al (2003) 1 4Fa n dG B e Ford et al (2002) 1 1Ga n dK L i Table 2. Data on the programme stars.…”

On the potassium-rotation connection in late-type Alpha Persei stars

“…Careful analysis of the subordinate lithium line at 610.4 nm by Ford, Jeffries & Smalley (2002) indicates that the spread in lithium abundances among Pleiades stars with the same mass may be real.…”