Photometric and spectroscopic monitoring of YSOs in nearby star-forming regions - I. Eruptive YSOs

Mid-infrared (mid-IR) variability in young stellar objects (YSOs) is driven by several physical mechanisms, which produce a variety of amplitudes and light-curve shapes. One of these mechanisms, variable disc accretion, is predicted by models of episodic accretion to drive secular variability, including in the mid-IR. Because the largest accretion bursts are rare, adding new objects to the YSO eruptive variable class aids our understanding of the episodic accretion phenomenon and its possible impact on stellar and planetary formation. A previous analysis of 6.5 yr of NeoWISE light curves (3-5 mu m) of similar to 7000 nearby YSOs found an increase in the fraction of variability and variability amplitude for objects at younger stages of evolution. To help interpret these light curves, we have obtained low- and high-resolution near-IR spectra of 78 objects from this sample of YSOs. In this work, we present the analysis of nine nearby YSOs (d<1 kpc) that show the characteristics of known classes of eruptive variable YSOs. We find one FU Orionis (FUor)-like source, one EX Lupi type object, and six YSOs with mixed characteristics or V1647 Ori like objects. The varied characteristics observed in our sample are consistent with recent discoveries of eruptive YSOs. We discuss how a wide range in YSO outburst parameters (central mass, maximum accretion rate during outburst, evolutionary stage, and/or instability leading to the outburst) may play a significant role in the observed spectrophotometric properties of YSO outbursts.