Kinematics of Vega-like stars: Lifetimes and temporal evolution of circumstellar dust disks

We have used the velocity dispersion as an age indicator to constrain the ages of a large sample of main sequence Vega-like stars in order to study the lifetimes and temporal evolution of the dust disks around them. We use Hipparcos mea- surements to compute stellar velocities in the sky plane. The velocity dispersion of Vega-like stars is found to be systematically smaller than that of the normal main sequence field stars for all spectral types, suggesting that the main sequence dusty systems, on average, are younger than normal field stars. The debris disks seem to survive longer around late type stars as compared to early type stars. Further, we find a strong correlation between fractional dust luminosity ( fd ≡ Ldust/L� ) and velocity dispersion of stars with dust disks. Fractional dust luminosity is found to drop off steadily with increasing stellar age from early pre-main sequence phase to late main sequence phase.