A helium spread among the main sequence stars in NGC 2808
| dc.creator | D'Antona, F. | |
| dc.creator | Bellazzini, M. | |
| dc.creator | Caloi, V. | |
| dc.creator | Pecci, F. Fusi | |
| dc.creator | Galleti, S. | |
| dc.creator | Rood, R. T. | |
| dc.date | 2005-05-17 | |
| dc.date.accessioned | 2026-07-07T11:24:23Z | |
| dc.date.available | 2026-07-07T11:24:23Z | |
| dc.description | We studied the color distribution of the main sequence of the Globular Cluster NGC 2808, based on new deep HST-WFPC2 photometry of a field in the uncrowded outskirts of the cluster. The color distribution of main sequence stars is wider than expected for a single stellar population, given our (carefully determined) measurement errors. About 20% of the sample stars are much bluer than expected and are most plausibly explained as a population having a much larger helium abundance than the bulk of the main sequence. We estimate that the helium mass fraction of these stars is Y ~ 0.4. NGC 2808 may have suffered self-enrichment, with different stellar populations born from the ejecta of the intermediate mass asymptotic giant branch (AGB) stars of the first generation. In addition to the Y=0.40 stars, roughly 30% of the stars should have Y distributed between 0.26-0.29 while 50% have primordial Y, to explain also the peculiar horizontal branch morphology. Three main stages of star formation are identified, the first with primordial helium content Y ~ 0.24, the second one born from the winds of the most massive AGBs of the first stellar generation (6-7msun), having Y ~ 0.4, and a third one born from the matter ejected from less massive AGBs (~ 3.5-4.5msun) with Y ~ 0.26-0.29. For a long hiatus of time (several 10^7yr) between the second and third generation, star formation might have been inhibited by the explosion of late Supernovae II deriving from binary evolution. | |
| dc.description | accepted for publication on "The Astrophysical Journal" | |
| dc.identifier | https://arxiv.org/abs/astro-ph/0505347 | |
| dc.identifier | http://arxiv.org/abs/astro-ph/0505347 | |
| dc.identifier | Astrophys.J.631:868-878,2005 | |
| dc.identifier | doi:10.1086/431968 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/195174 | |
| dc.subject | Astrophysics | |
| dc.title | A helium spread among the main sequence stars in NGC 2808 | |
| dc.type | text |