AAS 195th Meeting, January 2000
Session 3. Globular Clusters
Display, Wednesday, January 12, 2000, 9:20am-6:30pm, Grand Hall

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[3.02] Evidence for Deep Mixing in the Globular Cluster M~13

R. M. Cavallo (NASA/GSFC), N. M Nagar (U. of Maryland)

We present the results of a spectroscopic study of aluminum in 85 red-giant-branch (RGB) stars that covers a range of 3.5 magnitudes from the tip of the RGB in the globular cluster M~13. The aluminum abundance distribution is bimodal at all magnitudes according to the statistics determined with the KMM algorithm. The ratio of aluminum-strong to aluminum-normal stars remains constant as a function of V magnitude at 2.00~{±~0.12 (1{\sigma}) up to V~=~13.1. At brighter magnitudes, this ratio jumps to near 3 due to a sharp decrease in the number of aluminum-normal giants near the RGB tip. Although the analysis still suffers from small-number effects, the results thus far present evidence that deep mixing is occurring on the RGB in M~13 and that at least part of the observed high aluminum abundances are due to this deep mixing. Further analysis compares the aluminum abundances on the RGB to the horizontal-branch morphology in an attempt to discover a relationship between deep (helium) mixing and the second-parameter effect.

R.M.C acknowledges the National Academy of Sciences for support of his work.

The author(s) of this abstract have provided an email address for comments about the abstract: rob@shemesh.gsfc.nasa.gov

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