Near-IR Spectroscopic Monitoring of Class I Protostars: Variability of Accretion and Wind Indicators

TL;DR

This study monitored near-IR spectra of 19 embedded protostars over time, revealing variability in accretion and wind indicators, with implications for understanding the dynamics close to young stellar objects.

Contribution

First comprehensive near-IR spectroscopic variability study of Class I protostars over multiple timescales, linking accretion and wind processes.

Findings

All targets showed spectral variability.

Maximum variability increased with time interval.

Extinction varies on timescales as short as 2 days.

Abstract

We present the results of a program that monitored the near-IR spectroscopic variability of a sample of 19 embedded protostars. Spectra were taken on time intervals from 2 days to 3 years, over a wavelength range from 0.85 {\mu}m to 2.45 {\mu}m, for 4-9 epochs of observations per target. We found that the spectra of all targets are variable, and that every emission feature observed is also variable (although not for all targets). With one exception, there were no drastic changes in the continua of the spectra, nor did any line completely disappear, nor did any line appear that was not previously apparent. This analysis focuses on understanding the connection between accretion (traced by H Br $\gamma$ and CO) and the wind (traced by He I, [FeII], and sometimes H$_2$). For both accretion and wind tracers, the median variability was constant versus time interval between observations, however the maximum variability that we observed increased with time interval between observations. Extinction is observed to vary within the minimum sampling time of 2 days, suggesting extinguishing material within a few stellar radii at high disk latitudes. The variability of [FeII] and H$_2$ were correlated for most (but not all) of the 7 YSOs showing both features, and the amplitude of the variability depends on the veiling. Although the occurrence of CO and Br $\gamma$ emission are connected, their variability is uncorrelated, suggesting that these emissions originate in separate regions near the protostar (e.g., disk and wind).