Time-monitoring observations of Brγ emission from young stars

We present multiple epochs of near-infrared 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 Brγ transition of hydrogen, with a resolution of ≈3500. Epochs were taken over a span of >1 yr, sampling time-spacings of roughly 1 d, 1 month, and 1 yr. The majority of our targets show Brγ emission, and in some cases these are the first published detections. Time variability is seen in approximately half of the targets showing Brγ emission. We compare the observed variability with expectations for rotationally modulated accretion on to the central stars and time-variable continuum emission or extinction from matter in the inner disc. 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 time-scales and amplitudes, and a more conclusive comparison with theoretical models.