On the White Dwarf Cooling Sequence of the Globular Cluster ω Centauri

Calamida, A.; Corsi, C. E.; Bono, G.; Stetson, P. B.; Prada Moroni, P.; Degl'Innocenti, S.; Ferraro, I.; Iannicola, G.; Koester, D.; Pulone, L.; Monelli, M.; Amico, P.; Buonanno, R.; Caputo, F.; D'Odorico, S.; Freyhammer, L. M.; Marchetti, E.; Nonino, M.; Romaniello, M.
Bibliographical reference

The Astrophysical Journal, Volume 673, Issue 1, pp. L29-L33.

Advertised on:
1
2008
Number of authors
19
IAC number of authors
1
Citations
35
Refereed citations
27
Description
We present deep and precise photometry (F435W, F625W, F658N) of ω Cen collected with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). We have identified ~6500 white dwarf (WD) candidates, and the ratio of WD to main-sequence (MS) star counts is found to be at least a factor of 2 larger than the ratio of CO-core WD cooling to MS lifetimes. This discrepancy is not explained by the possible occurrence of a He-enhanced stellar population, since the MS lifetime changes by only 15% when changing from a canonical (Y=0.25) to a He-enhanced composition (Y=0.42). The presence of some He-core WDs seems able to explain the observed star counts. The fraction of He WDs required ranges from 10% to 80% depending on their mean mass, and it is at least 5 times larger than for field WDs. The comparison in the color-magnitude diagram between theory and observations also supports the presence of He WDs. Empirical evidence indicates that He WDs have been detected in stellar systems hosting a large sample of extreme horizontal branch stars, thus suggesting that a fraction of red giants might avoid the He-core flash. Based on observations collected with the Advanced Camera for Surveys on board the Hubble Space Telescope.
Related projects
NGC 2808 Globular Cluster
Milky Way and Nearby Galaxies
The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis
Martín
López Corredoira