In this paper we investigate the hot end of the horizontal branch (HE), presenting evolutionary constraints concerning the C-M diagram location and the gravity of hot HE stars. According to the adopted evolutionary scenario, we predict an upper limit for HE temperatures of about log T-e = 4.45, remarkably cooler than previous estimates. We find that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities. Finally, the problem of gaps in the HE distribution is discussed, suggesting that, at least in the case of the cluster NGC 6752, evolutionary gaps, a bimodal distribution of CNO, and stellar rotation should all play a negligible role.
THE HOT END OF EVOLUTIONARY HORIZONTAL BRANCHES
DEGL'INNOCENTI, SCILLA;
1995-01-01
Abstract
In this paper we investigate the hot end of the horizontal branch (HE), presenting evolutionary constraints concerning the C-M diagram location and the gravity of hot HE stars. According to the adopted evolutionary scenario, we predict an upper limit for HE temperatures of about log T-e = 4.45, remarkably cooler than previous estimates. We find that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities. Finally, the problem of gaps in the HE distribution is discussed, suggesting that, at least in the case of the cluster NGC 6752, evolutionary gaps, a bimodal distribution of CNO, and stellar rotation should all play a negligible role.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
