The accretion rates and mechanisms of Herbig Ae/Be stars
  This work presents a spectroscopic study of 163 Herbig Ae/Be stars. Amongst
these, we present new data for 30 objects. Stellar parameters such as
temperature, reddening, mass, luminosity and age are homogeneously determined.
Mass accretion rates are determined from $\rm H\alpha$ emission line
measurements. Our data is complemented with the X-Shooter sample from previous
studies and we update results using Gaia DR2 parallaxes giving a total of 78
objects with homogeneously determined stellar parameters and mass accretion
rates. In addition, mass accretion rates of an additional 85 HAeBes are
determined. We confirm previous findings that the mass accretion rate increases
as a function of stellar mass, and the existence of a different slope for lower
and higher mass stars respectively. The mass where the slope changes is
determined to be $3.98^{+1.37}_{-0.94}\,\rm M_{\odot}$. We discuss this break
in the context of different modes of disk accretion for low- and high mass
stars. Because of their similarities with T Tauri stars, we identify the
accretion mechanism for the late-type Herbig stars with the Magnetospheric
Accretion. The possibilities for the earlier-type stars are still open, we
suggest the Boundary Layer accretion model may be a viable alternative.
Finally, we investigated the mass accretion - age relationship. Even using the
superior Gaia based data, it proved hard to select a large enough sub-sample to
remove the mass dependency in this relationship. Yet, it would appear that the
mass accretion does decline with age as expected from basic theoretical
considerations.
