2010/08/26 by E. Dalessandro, M. Salaris, F. R. Ferraro +5 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Cluster (spacecraft) #Globular cluster #Helium #Horizontal branch #Luminosity #Luminosity function #Red-giant branch #Stars #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1111/j.1365-2966.2010.17479.x
Accepted for publication in the MNRAS (12 pages, 11 figures, 1 table)
arxiv created 2010/08/26 · openalex publication_date 2010/10/11 · arxiv updated 2015/05/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present an accurate analysis of the peculiar horizontal branch (HB) of the massive Galactic globular cluster NGC2808, based on high-resolution far-UV and optical images of the central region of the cluster obtained with the Hubble Space Telescope. We confirm the multimodal distribution of stars along the HB: four sub-populations separated by gaps are distinguishable. The detailed comparison with suitable theoretical models showed that (i) it is not possible to reproduce the luminosity of the entire HB with a single helium abundance, while an appropriate modelling is possible for three HB groups by assuming different helium abundances in the range 0.24 < deltaY < 0.4 that are consistent with the multiple populations observed in the main sequence; and (ii) canonical HB models are not able to properly match the observational properties of the stars populating the hottest end of the observed HB distribution, the so-called blue hook region. These objects are probably `hot flashers', stars that peel off the red giant branch before reaching the tip and ignite helium at high Teff. Both of these conclusions are based on the luminosity of the HB in the optical and ultraviolet bands and do not depend on specific assumptions about mass loss.