Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....108..271g&link_type=abstract
The Astronomical Journal, vol. 108, no. 1, p. 271-284
Other
18
Blue Stars, Lithium, Main Sequence Stars, Open Clusters, Stellar Interiors, Stellar Structure, Abundance, Metallicity, Resonance Lines, Tables (Data), Temperature Dependence
Scientific paper
We have determined equivalent widths for a number of atomic lines, including the lambda 6707 resonance doublet of Li, from spectra of a sample of candidate early-type high-velocity stars (including a number of blue straggler candidates) and low-velocity comparison stars. We find that the high-velocity candidates can be divided into three distinct groups: (1) stars with low abundances both of Li and of metals in general; (2) stars with low abundances of Li but only slight deficiencies of the other metals; and (3) stars with nearly normal amounts of both Li and other metals. We tentatively identify these groups as (1) halo and thick-disk blue stragglers; (2) old, thinnish disk blue stragglers; and (3) nearly normal Population l stars which probably lie in the tail of the usual Pop. l velocity distribution. The kinematic properties of the three groups are consistent with this interpretation. Li is a fragile element which is easily destroyed in the hot interiors of main-sequence stars, and has previously been shown to be depleted in the atmospheres of blue stragglers in the open cluster M67. Our results on objects that we have identified in this paper as old, halo or thick disk, field blue stragglers suggest that lithium depletion is a general property of blue stragglers; this argues that large scale mixing must be a part of any mechanism that produces blue stragglers. Our observations of low lithium abundances in a number of metal-normal, high-velocity, A stars, suggest that the high-latitude A stars observed by Rodgers an d collaborators are probably not produced in the collison of a Magellanic Cloud-like object with the Galactic disk in the past few Gyr. A more likely hypothesis (that is consistent with our lithium abundances) is that the high latitude, normal gravity, metal-rich, A star population consists primarily of blue stragglers. These data also have allowed a redetermination of the relationship between the Stromgren metallicity index delta mo and (M/H) for low-metallicity objects.
Glaspey John W.
Pritchet Chris J.
Stetson Peter B.
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