Based on observations made with the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory under the GTO programme ID 072.C-0488.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

Although the relation has been shown not to be reliable for ages greater than $\sim$ 2 Gyr (Pace & Pasquini 2004), it is still helpful to distinguish between active, young stars and chromospherically quiet, old stars.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... -4.93

A value $\log R'_{{\rm HK}}$ = -5.05 is given in Henry et al. (1996) leading to an age estimate of 6.3 Gyr.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... error

Presently on the order of 80 cm s^-1, this error represents the main limitation on the measurement precision, but it will improve soon thanks to an ongoing redefinition of the thorium lines used for the wavelength calibration. See also Lovis et al. (2005) for further details on the different error sources of the radial-velocity estimate.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... naturally

On the contrary, such a correlation is not expected with the gravitational-instability scenario. Recent simulations even lead to the opposite result (Cai et al. 2005).

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.