A very young, compact bipolar H2O maser outflow in the intermediate-mass star-forming LkHα 234 region

Abstract

We report multi-epoch Very Long Baseline Interferometry (VLBI) H2O maser observations towards the compact cluster of young stellar objects (YSOs) close to the Herbig Be star LkHα 234. This cluster includes LkHα 234 and at least nine more YSOs that are formed within projected distances of ∼10 arcsec (∼9000 au). We detect H2O maser emission towards four of these YSOs. In particular, our VLBI observations (including proper motion measurements) reveal a remarkable very compact (∼0.2 arcsec = ∼180 au), bipolar H2O maser outflow emerging from the embedded YSO Very Large Array (VLA) 2. We estimate a kinematic age of ∼40 yr for this bipolar outflow, with expanding velocities of ∼20 km s−1 and momentum rate ṀwVw ≃ 10−4–10−3 M⊙ yr−1 km s−1 × (Ω/4π), powered by a YSO of a few solar masses. We propose that the outflow is produced by recurrent episodic jet ejections associated with the formation of this YSO. Short-lived episodic ejection events have previously been found towards high-mass YSOs. We show now that this behaviour is also present in intermediate-mass YSOs. These short-lived episodic ejections are probably related to episodic increases in the accretion rate, as observed in low-mass YSOs. We predict the presence of an accretion disc associated with VLA 2. If detected, this would represent one of the few known examples of intermediate-mass stars with a disc–YSO–jet system at scales of a few hundred astronomical units.