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J. Buss (U. Wisconsin Oshkosh), J.G. Cohen, B.B. Behr (CalTech), M.M. Briley (U. Wisconsin Oshkosh)
Recent Keck LRIS spectra of faint stars in the Galactic globular cluster M71 have revealed anticorrelated star-to-star variations in CN and CH bands at the level of the main sequence. This result requires at least some component of the light element abundance variations (C, N, O, Na, Al, etc.) seen among the more luminous cluster members to be present before ascent up the red giant branch and the subsequent onset of deep mixing.
To explore whether or not similar variations in other light elements (namely Na, O, and Al) also exist among the faint stars of M71, we have obtained suitable Keck HIRES spectra of a sample of stars from the red giant branch tip down to the main sequence turn-off.
A preliminary examination of these spectra shows significant star-to-star O and Na abundance variations to at least as faint as MV \approx 2.5. This is more than a full magnitude before deep mixing is expected to begin in this cluster (if one interprets red giant branch luminosity function bumps as the destruction of the molecular weight gradient) and implies these inhomogeneities might also be present on the main sequence (as would be consistent with the earlier CN and CH results).
We will be reporting on a full model based analysis of Na, O, and Al for these and fainter spectra in an attempt to determine the extent of these inhomogeneities among the low luminosity stars of M71.
This work was supported in part by a grant from the National Science Foundation (AST-9624680 to MMB and AST-9819614 to JGC).
The author(s) of this abstract have provided an email address for comments about the abstract: mike@maxwell.phys.uwosh.edu