In the modern understanding of the nature of the UV excess in elliptical galaxies the main source of this radiation is identified with the hot horizontal branch (H-HB) stages of the old, high metallicity stars. Since bulges of galaxies can possess stars of very high metallicity, the question arises whether these type of stars can be detected in the mix of stellar populations. In particular, whether they are present in our own Bulge. For this purpose we examine the Colour-Magnitude Diagram (CMD) of a field near the Galactic Centre in the projected sky region of Terzan 1. In this CMD we notice a feature, which could be the trace of an old, high metallicity component. The feature in question is a sort of bow departing from the red clump located at about V = 22.5m and V - I = 3.8m, passing at V = 21m, and terminating in a group of blue faint objects approximately located at V = 23m and V - I = 2.2m. The analysis is made with the aid of single stellar populations (SSPs) and synthetic CMDs. We suggest that the bow of stars traces the core He-burning phase of old (similar to 13 Gyr) stars of very high metallicity, and that the faint stars of very blue colour (V - I) are the observational counterpart of their H-HB stages.
|Titolo:||Where are the hot horizontal branch stars in the Galactic Bulge?|
|Autori:||Bertelli G; Bressan A; Chiosi C; Ng YK|
|Data di pubblicazione:||1996|
|Appare nelle tipologie:||1.1 Journal article|