EDP Sciences
Free access
Volume 443, Number 2, November IV 2005
Page(s) 609 - 626
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20053452

A&A 443, 609-626 (2005)
DOI: 10.1051/0004-6361:20053452

On the ages of exoplanet host stars

C. Saffe, M. Gómez and C. Chavero

Observatorio Astronómico de Córdoba, Laprida 854, 5000 Córdoba, Argentina
    e-mail: [saffe;mercedes;carolina]@oac.uncor.edu

(Received 17 May 2005 / Accepted 2 August 2005)

We obtained spectra, covering the CaII H and K region, for 49 exoplanet host (EH) stars, observable from the southern hemisphere. We measured the chromospheric activity index, $R'{_{\rm HK}}$. We compiled previously published values of this index for the observed objects as well as the remaining EH stars in an effort to better smooth temporal variations and derive a more representative value of the average chromospheric activity for each object. We used the average index to obtain ages for the group of EH stars. In addition we applied other methods, such as: Isochrone, lithium abundance, metallicity and transverse velocity dispersions, to compare with the chromospheric results. The kinematic method is a less reliable age estimator because EH stars lie red-ward of Parenago's discontinuity in the transverse velocity dispersion vs dereddened B-V diagram. The chromospheric and isochrone techniques give median ages of 5.2 and 7.4 Gyr, respectively, with a dispersion of ~4 Gyr. The median age of F and G EH stars derived by the isochrone technique is ~1-2 Gyr older than that of identical spectral type nearby stars not known to be associated with planets. However, the dispersion in both cases is large, about ~2-4 Gyr. We searched for correlations between the chromospheric and isochrone ages and $L_{\rm IR}$/$L_{\rm *}$ (the excess over the stellar luminosity) and the metallicity of the EH stars. No clear tendency is found in the first case, whereas the metallicy dispersion seems to slightly increase with age.

Key words: stars: chromospheres -- stars: fundamental parameters -- stars: kinematics -- stars: planetary systems -- techniques: spectroscopic

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© ESO 2005