Comparison between accretion-related properties of Herbig Ae/Be and T Tauri stars

This paper summarizes several results concerning the comparison between accretion-related properties of cool (T Tauri; T < 7000 K, M < 1 M-circle dot) and hot (Herbig Ae/Be; 7000 K < T < 13000 K; 1 M-circle dot < M < 6 M-circle dot) pre-main sequence (PMS) stars. This comparison gives insight into the analogies/differences in the physics of the star-disk interaction and in the physical mechanisms driving disk dissipation. Several optical and near-IR line luminosities used for low-mass objects are also valid to estimate typical accretion rates for intermediate-mass stars under similar empirical expressions. In contrast, the Ha width at 10% of peak intensity is used as an accretion tracer for T Tauris, but is not reliable to estimate accretion rates for Herbig Ae/Bes. This can be explained as a consequence of the different stellar rotation rates that characterize both types of stars. In addition, there are similar trends when the accretion rate is related to the near-IR colours and disk masses, suggesting that viscous accretion disk models are able to explain these trends for both T Tauri and Herbig Ae/Be stars. However, there are two major differences between cool and hot PMS objects. First, the inner gas dissipation timescale, as estimated by relating the accretion rates and the stellar ages, is slightly faster for Herbig Ae/Be stars. This could have implications on the physical mechanism able to form planets around objects more massive than the Sun. Second, the relative position of Herbig Ae/Bes with disks showing signs of inner dust clearing in the accretion rate-disk mass plane contrasts with that of transitional T Tauri stars, when both samples are compared with classical, non-evolved disks. This latter difference could be pointing to a different physical mechanism driving disk evolution, depending on the stellar regime. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim