Observing variability in young stellar objects in the infrared

Young stellar objects (YSOs) are characterised by accretion of matter through disks and ejection through jets. Both mechanisms are closely associated, however, their link is still not completely understood. In the past, these processes have been considered steady. Most recent observations, supported by theoretical models, indicate, however, that they are mostly episodic for a large range of stellar masses and ages and play a fundamental role in protostellar evolution. We have been using spectroscopic and imaging data from VLTI/ISAAC and SINFONI from different epochs (2005 and 2013) in the NIR to probe the kinematic and dynamic properties of IRS54, a very low-mass YSO, (0.2 Msun, Lbol ~0.78Lsun, Class I YSO) in the J, H, and K bands. To investigate the variability, we used the line emission of [FeII] (at 1.257, 1.644 microns) and BrG (2.166 microns). Correcting for visual extinction (~16mag in 2005 and ~29mag in 2013), we calculated the mass accretion rate to be ~5 x 10^-9 Msun yr-1 in 2005 and ~1 x 10^-7 Msun yr-1 in 2013. We found that its large variability is due to episodic accretion, making IRS54 the lowest mass outbursting YSO ever detected