S255IR NIRS3 NIR adaptive optics imaging

We discovered a new near infrared knot north-east of NIRS3 that we interpret as a jet knot that was ejected during the last accretion outburst and observed in the radio regime as part of a follow-up after the outburst. We measured a mean tangential velocity for this knot of 450+/-50km/s. We analysed the continuum-subtracted images from H_2_, which traces jet-shocked emission, and Br{gamma}, which traces scattered light from a combination of accretion activity and UV radiation from the central massive protostar.

We observed a significant decrease in flux at the location of NIRS3, with K=13.48mag being the absolute minimum in the historic series. Our observations strongly suggest a scenario where the episodic accretion is followed by an episodic ejection response in the near infrared, as was seen in the earlier radio follow-up. The ~2um photometry from the past 30 years suggests that NIRS3 might have undergone another outburst in the late 1980s, making it the first massive protostar with such evidence observed in the near infrared.