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 ^ { \prime } { { } _ { 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 \sim 4 Gyr .
The median age of F and G EH stars derived by the isochrone technique is \sim 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 \sim 2–4 Gyr .
We searched for correlations between the chromospheric and isochrone ages and L _ { IR } /L _ { * } ( 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 .