Nordstrom et al. 2004 Review

Geneva-Copenhagen Survey of the Solar Neighborhood





Derivation of age:

• chromospheric activity
• evolutionary tracks (isochrones)

Chromospheric Age:

• decline of stellar activity with age (Soderblom et al. 1991)
• good for F, G, and K-type stars younger than the sun
• no good for binary systems (which affect Prot, and therefore activity)
• most stars in survey were older than the sun, so ages were calculated using isochrones

Isochrones:

• Use theoretically computed isochrones for comparison (Edvardsson et al 1993)
• Use measured T(eff), M(v) and [Fe/H]
• models compared in the log(Teff) - M(v) plane
• Models applied:
• younger stars --> Padova models (Girardi et al. 2000, Salasnich et al. 2000)
• older stars (t >17.8Gyr) --> Geneva models (Mowlavi et al. 1998, Lejeune & Schaerer 2001)
• mostly used Padova models since the survey did not include many stars older than 17.8 Gyr
• chemical composition input
• solar composition models w/defined alpha-enhancement (VandenBerg 2000)