A spectroscopic survey of Herbig Ae/Be stars with X-Shooter I: Stellar parameters and accretion rates

TL;DR

This study provides the largest spectroscopic survey of Herbig Ae/Be stars, analyzing their stellar parameters and accretion rates, revealing correlations with stellar properties and potential different accretion mechanisms in Herbig Be stars.

Contribution

It offers a homogeneous analysis of 91 Herbig Ae/Be stars using VLT/X-Shooter spectra, and models UV data to directly measure accretion rates, highlighting differences between Herbig Ae and Be stars.

Findings

Young, massive stars are the strongest accretors.

Accretion luminosity correlates with stellar luminosity.

Potential alternative accretion mechanisms in Herbig Be stars.

Abstract

Herbig Ae/Be stars span a key mass range that links low and high mass stars, and thus provide an ideal window from which to explore their formation. This paper presents VLT/X-Shooter spectra of 91 Herbig Ae/Be stars, HAeBes; the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultra-violet (UV) are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within the Herbig Be mass range.