2012/02/20 by Alberto Buzzoni, Emanuele Bertone, Giovanni Carraro +1 · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Balmer series #Cluster (spacecraft) #Elliptical galaxy #Galaxies: Formation, Evolution, Phenomena #Galaxy #Luminosity #Open cluster #Photometry (optics) #Star cluster #Stellar mass #Stellar, planetary, and galactic studies #Ultraviolet #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/749/1/35
A total of 15 pages, with 9 figures and 3 tables. The paper is to appear in the Astrophysical Journal. See http://www.bo.astro.it/~eps/home.html for further data retrieval and future track of the project
arxiv created 2012/02/20 · openalex publication_date 2012/03/20 · arxiv updated 2015/06/04 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The evolutionary properties of the old metal-rich Galactic open cluster NGC 6791 are assessed based on deep UB photometry and Two Micron All Sky Survey JK data. For the 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical ( U − B ) and ( J − K ) color fitting. The derived H-R diagram has been matched with the Uvblue grid of synthetic stellar spectra to obtain the integrated spectral energy distribution (SED) of the system, together with a full set of UV (Fanelli) and optical (Lick) narrowband indices. The total bolometric magnitude of NGC 6791 is M bol 6791 = −6.29, with a color ( B − V ) 6791 = 0.97. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000 Å Balmer break, and a lower Mg 2 index. The confirmed presence of a dozen hot stars along their extreme horizontal-branch evolution leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7% ± 0.4% of the total bolometric luminosity emitted shortward of 2500 Å. The cluster helium abundance results in Y 6791 = 0.30 ± 0.04, while the post-main-sequence (PMS) implied stellar lifetime from star number counts fairly agrees with the theoretical expectations from both the Padova and Basti stellar tracks. A PMS fuel consumption of 0.43 ± 0.01 M ☉ is found for NGC 6791 stars, in close agreement with the estimated mass of cluster He-rich white dwarfs. Such a tight figure may lead one to suspect that a fraction of the cluster stellar population does not actually reach the minimum mass required to effectively ignite He in the stellar core.