Tracing Accretion onto Herbig Ae/Be Stars Using the Br\gamma\ Line

TL;DR

This study investigates accretion processes in Herbig Ae/Be stars using high-resolution near-infrared spectra, revealing correlations with stellar properties and examining the influence of disk structure and variability on accretion indicators.

Contribution

It provides a comprehensive analysis of accretion in intermediate-mass pre-main-sequence stars using a large sample and new high-resolution spectra, highlighting the relationship between accretion and stellar characteristics.

Findings

Positive correlation between Brγ and stellar luminosity with a slope change between groups.

Accretion luminosity and rate depend on stellar mass and age, but not when normalized by stellar luminosity.

No significant correlation between disk dust structure and accretion activity.

Abstract

Accretion plays an important role in protoplanetary disk evolution, and it is thought that the accretion mechanism changes between low- and high-mass stars. Here, we characterize accretion in intermediate-mass, pre-main-sequence Herbig Ae/Be (HAeBe) stars to search for correlations between accretion and system properties. We present new high-resolution, near-infrared spectra from the Immersion GRating INfrared Spectrograph for 102 HAeBes and analyze the accretion-tracing Br$\gamma$ line at 2.166 $\mu$m. We also include the samples of Fairlamb et al. and Donehew & Brittain, for a total of 155 targets. We find a positive correlation between the Br$\gamma$ and stellar luminosity, with a change in the slope between the Herbig Aes and Herbig Bes. We use $L_{Br\gamma}$ to determine the accretion luminosity and accretion rate. We find that the accretion luminosity and rate depend on stellar mass and age; however, the trend disappears when normalizing the accretion luminosity by the stellar luminosity. We classify the objects into flared (Group I) or flat (Group II) disks and find that there is no trend with accretion luminosity or rate, indicating that the disk dust structure is not impacting accretion. We test for Br$\gamma$ variability in objects that are common to our sample and previous studies. We find that the Br$\gamma$ line equivalent width is largely consistent between the literature observations and those that we present here, except in a few cases where we may be seeing changes in the accretion rate.