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Isochrones for Old (> 5 Gyr) Stars and Stelllar Populations. I. Models for-2.4 <= [Fe/H] <=+0.6, 0.25 <= Y <= 0.33, and-0.4 <= [alpha/Fe] <=+0.4
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
2014 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 794, no 1, UNSP 72- p.Article in journal (Refereed) Published
Abstract [en]

Canonical grids of stellar evolutionary sequences have been computed for the helium mass-fraction abundances Y = 0.25, 0.29, and 0.33, and for iron abundances that vary from 2.4 to +0.4 (in 0.2 dex increments) when [alpha/Fe] = +0.4, or for the ranges 2.0 <= [Fe/H] <= +0.6, 1.8 <= [Fe/H] <= +0.6 when [alpha/Fe] = 0.0 and -0.4, respectively. The grids, which consist of tracks for masses from 0.12 M-circle dot to 1.1-1.5 M-circle dot (depending on the metallicity) are based on up-to-date physics, including the gravitational settling of helium (but not metals diffusion). Interpolation software is provided to generate isochrones for arbitrary ages between approximate to 5 and 15 Gyr and any values of Y, [alpha/Fe], and [Fe/H] within the aformentioned ranges. Comparisons of isochrones with published color magnitude diagrams (CMDs) for the open clusters M67 ([Fe/H] approximate to 0.0) and NGC 6791 ([Fe/H] approximate to 0.3) and for four of the metal-poor globular clusters (47 Tuc, M3, M5, and M92) indicate that the models for the observed metallicities do a reasonably good job of reproducing the locations and slopes of the cluster main sequences and giant branches. The same conclusion is reached from a consideration of plots of nearby subdwarfs that have accurate Hipparcos parallaxes and metallicities in the range -2.0 <= [Fe/H] <= -1.0 on various CMDs and on the (log T-eff, M-V) diagram. A relatively hot temperature scale similar to that derived in recent calibrations of the infrared flux method is favored by both the isochrones and the adopted color transformations, which are based on the latest MARCS model atmospheres.

Place, publisher, year, edition, pages
2014. Vol. 794, no 1, UNSP 72- p.
Keyword [en]
globular clusters: individual (47 Tuc, M3, M5, M92), open clusters and associations: individual (M67, NGC 6791), stars: abundances, stars: evolution, stars: Population II
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-236036DOI: 10.1088/0004-637X/794/1/72ISI: 000342581200072OAI: oai:DiVA.org:uu-236036DiVA: diva2:764268
Available from: 2014-11-18 Created: 2014-11-12 Last updated: 2014-11-18Bibliographically approved

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Edvardsson, Bengt
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