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EnglishThis is the first of a series of papers devoted to a global study of the photometric properties of the red stellar sequences in a complete sample of the Large Magellanic Cloud clusters, by means of near-infrared array photometry. Deep J, H, Ks photometry and accurate color-magnitude diagrams down to K~18.5, i.e., ~1.5 mag below the red He clump, for six intermediate-age clusters (namely, NGC 1987, NGC 2108, NGC 2190, NGC 2209, NGC 2231, NGC 2249) are presented. A quantitative estimate of the population ratios (by number and luminosity) between red giant branch (RGB) and He-clump stars for each target cluster is provided and discussed in the framework of probing the so-called RGB phase transition (Ph-T). By using the Elson & Fall s-parameter as an age indicator, the observed RGB population shows a sharp enhancement (in both number and luminosity) at s=36. Obviously, the corresponding absolute age strictly depends on the details of theoretical models adopted to calibrate the s-parameter. Curiously, the currently available calibrations of the s-parameter in terms of age based on canonical (by Elson & Fall) and overshooting (Girardi and coworkers) models provide ages that well agree within 10%, suggesting that the full development of the RGB occurs at t~700 Myr and is a relatively fast event (deltat~300 Myr). However, the RGB Ph-T epoch derived from the overshooting calibration of the s-parameter turns out to be significantly earlier than the epoch provided by the recent evolutionary tracks by Girardi and coworkers. A new calibration of the s-parameter based on high-quality color-magnitude diagrams and updated models is urged to address the origin of this discrepancy and finally establish the epoch of the RGB Ph-T.
| Titolo: | Probing the Red Giant Branch Phase Transition: Near-Infrared Photometry of Six Intermediate-Age Large Magellanic Cloud Clusters |
| Autore/i: | FERRARO, FRANCESCO ROSARIO; ORIGLIA L.; TESTA V.; MARASTON C. |
| Autore/i Unibo: | |
| Anno: | 2004 |
| Rivista: | |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.1086/420837 |
| Abstract: | This is the first of a series of papers devoted to a global study of the photometric properties of the red stellar sequences in a complete sample of the Large Magellanic Cloud clusters, by means of near-infrared array photometry. Deep J, H, Ks photometry and accurate color-magnitude diagrams down to K~18.5, i.e., ~1.5 mag below the red He clump, for six intermediate-age clusters (namely, NGC 1987, NGC 2108, NGC 2190, NGC 2209, NGC 2231, NGC 2249) are presented. A quantitative estimate of the population ratios (by number and luminosity) between red giant branch (RGB) and He-clump stars for each target cluster is provided and discussed in the framework of probing the so-called RGB phase transition (Ph-T). By using the Elson & Fall s-parameter as an age indicator, the observed RGB population shows a sharp enhancement (in both number and luminosity) at s=36. Obviously, the corresponding absolute age strictly depends on the details of theoretical models adopted to calibrate the s-parameter. Curiously, the currently available calibrations of the s-parameter in terms of age based on canonical (by Elson & Fall) and overshooting (Girardi and coworkers) models provide ages that well agree within 10%, suggesting that the full development of the RGB occurs at t~700 Myr and is a relatively fast event (deltat~300 Myr). However, the RGB Ph-T epoch derived from the overshooting calibration of the s-parameter turns out to be significantly earlier than the epoch provided by the recent evolutionary tracks by Girardi and coworkers. A new calibration of the s-parameter based on high-quality color-magnitude diagrams and updated models is urged to address the origin of this discrepancy and finally establish the epoch of the RGB Ph-T. |
| Data prodotto definitivo in UGOV: | 2005-10-17 22:11:22 |
| Appare nelle tipologie: | 1.01 Articolo in rivista |
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http://hdl.handle.net/11585/1475
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