Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71 II. Iron.pdfVIP

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Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71 II. Iron.pdf

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Abundances in Stars from the Red Giant Branch Tip to the Near Main Sequence in M71 II. Iron

a r X i v : a s t r o - p h / 0 1 0 3 4 9 4 v 2 2 2 M a y 2 0 0 1 AJ, in press (Sep. 2001) Abundances in Stars from the Red Giant Branch Tip to the Near the Main Sequence Turn Off in M71: II. Iron Abundance 1 Solange V. Ram??rez 2, Judith G. Cohen2, Jeremy Buss3 and Michael M. Briley3 ABSTRACT We present [Fe/H] abundance results that involve a sample of stars with a wide range in luminosity from luminous giants to stars near the turnoff in a globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II lines in high dispersion spectra observed with HIRES at the W. M. Keck Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines agree with each other and with earlier determinations. Also the [Fe/H] obtained from Fe I and Fe II lines is constant within the rather small uncertainties for this group of stars over the full range in Teff and luminosity, suggesting that NLTE effects are negligible in our iron abundance determination. In this globular cluster, there is no difference among the mean [Fe/H] of giant stars located at or above the RHB, RHB stars, giant stars located below the RHB and stars near the turnoff. Subject headings: globular clusters: general — globular clusters: individual (M71) — stars: evolution – stars:abundances 1. INTRODUCTION Abundance determinations of stars in Galactic globular clusters can provide valuable informa- tion about important astrophysical processes such as stellar evolution, stellar structure, Galactic chemical evolution and the formation of the Milky Way. Surface stellar abundances of C, N, O, and often Na, Mg, and Al are found to be variable among red giants within a globular cluster. The physical process responsible of these star-to-star element variations is still uncertain (see Cohen et al. 2001, Paper I). 1Based on observations obtain