2007/01/23 by A. Mucciarelli, Alessio Mucciarelli, Francesco R. Ferraro +5 · 4 citations
Mathematics · Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Cluster (spacecraft) #Computer science #Diagram #Elliptical galaxy #Galaxy #Globular cluster #Hubble sequence #Hubble space telescope #Large Magellanic Cloud #Mathematics #Metallicity #Open cluster #Physics #Population #Red-giant branch #Small Magellanic Cloud #Star cluster #Star formation #Stars #Statistics #Stellar evolution #Stellar population #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/513076
published as Astron.J.133:2053-2060,2007 · 26 pages, 8 figures, accepted to AJ
arxiv created 2007/01/23 · openalex publication_date 2007/03/26 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have used deep, high-resolution Hubble Space Telescope ACS observations to image the cluster NGC 1978 in the Large Magellanic Cloud. This high-quality photometric data set allowed us to confirm the high ellipticity ( ∼ 0.30 ± 0.02) of this stellar system. The derived color-magnitude diagram allowed a detailed study of the main evolutionary sequences; in particular, we have detected the so-called bump along the red giant branch (at V 555 = 19.10 ± 0.10). This is the first detection of this feature in an intermediate-age cluster. Moreover, the morphology of the evolutionary sequence and the population ratios have been compared with the expectations of different theoretical models (namely, BaSTI, Pisa Evolutionary Library [PEL], and Padua) in order to quantify the effect of convective overshooting. The best agreement (in terms of both morphology and star counts) has been found within the PEL isochrone, with Z = 0.008 (consistent with the most recent determination of the cluster metallicity, [M/H] = -0.37 dex) and a mild overshooting efficiency (Λ os = 0.1). By adopting this theoretical set an age of τ = 1.9 ± 0.1 Gyr has been obtained.