A Superwind from Early Post–Red Giant Stars?

We suggest that the gap observed at ~20,000 K in the horizontal branches of several Galactic globular clusters is caused by a small amount of extra mass loss that occurs when stars start to "peel off" the red giant branch (RGB), i.e., when their effective temperature starts to increase, even though they may still be on the RGB. We show that the envelope structure of RGB stars that start to peel off is similar to that of late asymptotic giant branch stars known to have a superwind phase. An analogous superwind in the RGB peel-off stars could easily lead to the observed gap in the distribution of the hottest horizontal-branch stars.