Time-monitoring Observations of Br$\gamma$ Emission from Young Stars

TL;DR

This study presents multi-epoch near-infrared spectroscopy of 25 young stars, revealing variability in BrGamma emission that challenges existing models of magnetospheric accretion.

Contribution

First multi-epoch near-IR spectroscopic survey of young stars focusing on BrGamma emission variability over diverse timescales.

Findings

Most targets show BrGamma emission, some detected for the first time.

Approximately half of the emission sources exhibit variability.

Observations do not fully align with models of rotationally-modulated magnetospheric accretion.

Abstract

We present multiple epochs of near-IR spectroscopy for a sample of 25 young stars, including T Tauri, Herbig Ae/Be, and FU Ori objects. Using the FSPEC instrument on the Bok 90-inch telescope, we obtained K-band spectra of the BrGamma transition of hydrogen, with a resolution of ~3500. Epochs were taken over a span of >1 year, sampling time-spacings of roughly one day, one month, and one year. The majority of our targets show BrGamma emission, and in some cases these are the first published detections. Time-variability is seen in approximately half of the targets showing BrGamma emission. We compare the observed variability with expectations for rotationally-modulated accretion onto the central stars and time-variable continuum emission or extinction from matter in the inner disk. Our observations are not entirely consistent with models of rotationally-modulated magnetospheric accretion. Further monitoring, over a larger number of epochs, will facilitate more quantitative constraints on variability timescales and amplitudes, and a more conclusive comparison with theoretical models.