A very young, compact bipolar H$_2$O maser outflow in the intermediate-mass star-forming LkH$alpha$ 234 region

We report multi-epoch VLBI H$_2$O maser observations towards the compact cluster of YSOs close to the Herbig Be star LkH$alpha$ 234. This cluster includes LkH$alpha$ 234 and at least nine more YSOs that are formed within projected distances of $sim$10 arcsec ($sim$9,000 au). We detect H$_2$O maser emission towards four of these YSOs. In particular, our VLBI observations (including proper motion measurements) reveal a remarkable very compact ($sim$0.2 arcsec = $sim$180 au), bipolar H$_2$O maser outflow emerging from the embedded YSO VLA 2. We estimate a kinematic age of $sim$40 yr for this bipolar outflow, with expanding velocities of $sim$20 km s$^{-1}$ and momentum rate $dot M_w V_w$ $simeq$ $10^{-4}-10^{-3}$ M$_{odot}$ yr$^{-1}$ km s$^{-1}$$times (Omega$/$4pi)$, 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 disk associated with VLA 2. If detected, this would represent one of the few known examples of intermediate-mass stars with a disk-YSO-jet system at scales of a few hundred au.

Multi-epoch VLBA H$_2$O maser observations toward the massive YSOs AFGL 2591 VLA 2 and VLA 3

We present multi-epoch Very Long Baseline Array (VLBA) H$_2$O maser observations toward the massive young stellar objects (YSOs) VLA 2 and VLA 3 in the star-forming region AFGL 2591. Through these observations, we have extended the study of the evolution of the masers towards these objects up to a time span of $sim$ 10 yrs, measuring their radial velocities and proper motions. The H$_2$O masers in VLA 3, the most massive YSO in AFGL 2591 ($sim$ 30--40~M$_{odot}$), are grouped within projected distances of $lesssim$ 40 mas ($lesssim$ 130 AU) from VLA 3. In contrast to other H$_2$O masers in AFGL 2591, the masers associated with VLA 3 are significantly blueshifted (up to $sim$ 30 km s$^{-1}$) with respect to the velocity of the ambient molecular cloud. We find that the H$_2$O maser cluster as a whole, has moved westwards of VLA~3 between the 2001 and 2009 observations, with a proper motion of $sim$ 1.2 mas yr$^{-1}$ ($sim$ 20 km s$^{-1}$). We conclude that these masers are tracing blueshifted outflowing material, shock excited at the inner parts of a cavity seen previously in ammonia molecular lines and infrared images, and proposed to be evacuated by the outflow associated with the massive VLA 3 source. The masers in the region of VLA 2 are located at projected distances of $sim$ 0.7$$ ($sim$ 2300 AU) north from this source, with their kinematics suggesting that they are excited by a YSO other than VLA 2. This driving source has not yet been identified.

High Angular Resolution Observations at 7-mm of the Core of the Quadrupolar HH 111/121 Outflow

We present sensitive, high angular resolution ($0rlap.{}05$) VLA continuum observations made at 7 mm of the core of the HH 111/121 quadrupolar outflow. We estimate that at this wavelength the continuum emission is dominated by dust, although a significant free-free contribution ($sim$30%) is still present. The observed structure is formed by two overlapping, elongated sources approximately perpendicular to each other as viewed from Earth. We interpret this structure as either tracing two circumstellar disks that exist around each of the protostars of the close binary source at the core of this quadrupolar outflow or a disk and a jet perpendicular to it. Both interpretations have advantages and disadvantages, and future high angular resolution spectroscopic millimeter observations are required to favor one of them in a more conclusive way.

The Circumstellar Structure and Excitation Effects around the Massive Protostar Cepheus A HW 2

We report SMA 335 GHz continuum observations with angular resolution of ~0.3, together with VLA ammonia observations with ~1 resolution toward Cep A HW 2. We find that the flattened disk structure of the dust emission observed by Patel et al. is preserved at the 0.3 scale, showing an elongated structure of ~$0.6 size (450 AU) peaking on HW 2. In addition, two ammonia cores are observed, one associated with a hot-core previously reported, and an elongated core with a double peak separated by ~1.3 and with signs of heating at the inner edges of the gas facing HW 2. The double-peaked ammonia structure, as well as the double-peaked CH3CN structure reported previously (and proposed to be two independent hot-cores), surround both the dust emission as well as the double-peaked SO2 disk structure found by Jimenez-Serra et al. All these results argue against the interpretation of the elongated dust-gas structure as due to a chance-superposition of different cores; instead, they imply that it is physically related to the central massive object within a disk-protostar-jet system.