A spectroscopic survey of Herbig Ae/Be stars with X-Shooter II: Accretion diagnostic lines

TL;DR

This study investigates accretion in 91 Herbig Ae/Be stars using spectroscopic data, identifying multiple emission lines as reliable accretion tracers and analyzing their relation to accretion luminosity.

Contribution

It expands the set of known accretion diagnostic lines in Herbig Ae/Be stars by tenfold and compares their luminosities with accretion luminosities across a broad spectral range.

Findings

All emission lines studied correlate with accretion luminosity.

The average accretion-to-line luminosity relation is approximately L_acc ∝ L_line^1.16.

Emission lines can serve as effective accretion tracers in Herbig Ae/Be stars.

Abstract

The Herbig Ae/Be stars (HAeBes) allow an exploration of the properties of Pre-Main Sequence(PMS) stars above the low-mass range ($<2{\rm\thinspace M_{\odot}}$) and those bordering the high-mass range ($>8{\rm\thinspace M_{\odot}}$). This paper is the second in a series exploring accretion in 91 HAeBes with Very Large Telescope/X-shooter spectra. Equivalent width measurements are carried out on 32 different lines, spanning the UV to NIR, in order to obtain their line luminosities. The line luminosities were compared to accretion luminosities, which were determined directly from measurements of an UV-excess. When detected, emission lines always demonstrate a correlation with the accretion luminosity, regardless of detection frequency. The average relationship between accretion luminosity and line luminosity is found to be ${\thinspace L_{\rm acc}}\propto{\thinspace L_{\rm line}}^{1.16 \pm 0.15}$. This is in agreement with the findings in Classical T Tauri stars, although the HAeBe relationship is generally steeper, particularly towards the Herbig Be mass range. Since all observed lines display a correlation with the accretion luminosity, all of them can be used as accretion tracers. This has increased the number of accretion diagnostic lines in HAeBes tenfold. However, questions still remain on the physical origin of each line, which may not be due to accretion.