On the mass accretion rate and infrared excess in Herbig Ae/Be Stars.

The present study makes use of the unprecedented capability of the Gaia mission to obtain the stellar parameters such as distance, age, and mass of HAeBe stars. The accuracy of Gaia DR2 astrometry is demonstrated from the comparison of the Gaia DR2 distances of 131 HAeBe stars with the previously estimated values from the literature. This is one of the initial studies to estimate the age and mass of a confirmed sample of HAeBe stars using both the photometry and distance from the Gaia mission. Mass accretion rates are calculated from H alpha line flux measurements of 106 HAeBe stars. Since we used distances and the stellar masses derived from the Gaia DR2 data in the calculation of the mass accretion rate, our estimates are more accurate than previous studies. The mass accretion rate is found to decay exponentially with age, from which we estimated a disk dissipation timescale of 1.9 +/- 0.1 Myr. The mass accretion rate and stellar mass exhibit a power-law relation of the form M over dot( acc) proportional to M-*(2.8 +/- 0.2). From the distinct distribution in the values of the infrared spectral index, n(2-4.6), we suggest the possibility of difference in the disk structure between Herbig Be and Herbig Ae stars.