Physics
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997esasp.402..231l&link_type=abstract
Proceedings of the ESA Symposium `Hipparcos - Venice '97', 13-16 May, Venice, Italy, ESA SP-402 (July 1997), p. 231-236
Physics
10
Scientific paper
The observational main sequence of the Hyades cluster resulting from the careful analysis of the Hipparcos data by Brown et al. (1997) is analysed by means of modern theoretical stellar evolution models with the objectives of determining the helium content and the age of the cluster. In a first step we have calculated zero age main-sequence models in a mass range from 0.8 to 1.6 M_(solar) for various chemical compositions. The input physics includes the most recent opacity data and an appropriate equation of state. We have adopted the solar value of the mixing-length (l = 1.64 pressure scale-heights) derived from solar calibration with the same input physics. Interpolation in chemical composition of the theoretical zero-age main sequence lines is performed in order to reproduce the observed lowest part of the HR diagram, composed of the less massive stars which do not significantly depart from the ZAMS line. This provides the helium content Y, in mass fraction, of the cluster (Y=0.26 =/- 0.02), the metallicity of which (Z=0.024 +/- 0.004) being determined independently by detailed spectroscopic analysis. This part is discussed with more details by Cayrel de Strobel et al. (1997). In a second step we have calculated evolved stellar models with the same input physics, with and without overshooting, adopting Y=0.26 and Z=0.024. We compare the associated isochrones to the whole observational main sequence of the cluster in the (M_V, B-V) diagram. Our results suggest a cluster age of 625 Myr with observational indications for the presence of overshooting. We estimate that the uncertainty on age is at least 50 Myr.
Gomez Ana E.
Lebreton Yveline
Mermilliod Jean-Claude
Perryman Michael . A. C.
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