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

TL;DR

This paper compares accretion properties of Herbig Ae/Be and T Tauri stars, revealing similarities in disk accretion trends but also key differences in gas dissipation timescales and disk evolution mechanisms, impacting planet formation theories.

Contribution

It provides a comparative analysis of accretion processes in intermediate-mass and low-mass pre-main sequence stars, highlighting differences in disk evolution and gas dissipation timescales.

Findings

Accretion rate estimators are valid for both star types, except Halpha width for Herbig Ae/Be.

Inner gas dissipation is faster in Herbig Ae/Be stars.

Different disk evolution mechanisms are suggested for each stellar regime.

Abstract

This paper summarizes several results concerning the comparison between accretion-related properties of cool (T Tauri; T < 7000 K, M < 1 Msun and hot (Herbig Ae/Be; 7000 < T(K) < 13000; 1 < M(Msun) < 6) 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 Halpha 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.