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C. A. Pilachowski (National Optical Astronomy Observatories), C. Sneden (University of Texas at Austin)
H-alpha profiles of 264 giants in the globular clusters M3, M13, M15, and M92 obtained with the Hydra Multi-object Spectrograph on the 3.5-m WIYN Telescope have been examined for the presence of emission. The percentage of giants showing H-alpha emission rises from near zero at MV~--1.5 to 100% at MV~--2.4, at the tip of the red giant branch.
In addition to the expected emission profiles found in tip giants, asymptotic giant branch stars in M15, and possibly M13, also show emission. The emission, which is seen in both the red and the blue wings, is sometimes strong and can be variable. These stars have absolute magnitudes near MV~--1 and B-V~0.75, and do not appear to be photometric or radial velocity variables. While the H-alpha profiles are consistent with the presence of circumstellar material in these post-HB giants, the origin of such material at this evolutionary phase is not understood. ~ ~ ~