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Register a new userSMA observations towards the compact, short-lived bipolar water maser outflow in the LkH{alpha} 234 region
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Josep Miquel Girart
Publication date
2016
fields
Physics
and research's language is
English
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We present Submillimeter Array (SMA) 1.35 mm subarcsecond angular resolution observations toward the LkH{alpha} 234 intermediate-mass star-forming region. The dust emission arises from a filamentary structure of $sim$5 arcsec ($sim$4500 au) enclosing VLA 1-3 and MM 1, perpendicular to the different outflows detected in the region. The most evolved objects are located at the southeastern edge of the dust filamentary structure and the youngest ones at the northeastern edge. The circumstellar structures around VLA 1, VLA 3, and MM 1 have radii between $sim$200 and $sim$375 au and masses in the $sim$0.08-0.3 M$_{odot}$ range. The 1.35 mm emission of VLA 2 arises from an unresolved (r$< 135$ au) circumstellar disk with a mass of $sim$0.02 M$_{odot}$. This source is powering a compact ($sim$4000 au), low radial velocity ($sim$7 km s$^{-1}$) SiO bipolar outflow, close to the plane of the sky. We conclude that this outflow is the large-scale counterpart of the short-lived, episodic, bipolar outflow observed through H$_2$O masers at much smaller scales ($sim $180 au), and that has been created by the accumulation of the ejection of several episodic collimated events of material. The circumstellar gas around VLA 2 and VLA 3 is hot ($sim$130 K) and exhibits velocity gradients that could trace rotation. There is a bridge of warm and dense molecular gas connecting VLA 2 and VLA 3. We discuss the possibility that this bridge could trace a stream of gas between VLA 3 and VLA 2, increasing the accretion rate onto VLA 2 to explain why this source has an important outflow activity.
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We report multi-epoch VLBI H$_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.
We investigate the kinematics of high mass protostellar objects within the high mass star forming region IRAS 19410+2336. We performed high angular resolution observations of 6.7-GHz methanol and 22 GHz water masers using the MERLIN (Multi-Element Radio Linked Interferometer Network) and e-MERLIN interferometers. The 6.7-GHz methanol maser emission line was detected within the $sim$ 16--27 km s$^{-1}$ velocity range with a peak flux density $sim$50 Jy. The maser spots are spread over $sim$1.3 arcsec on the sky, corresponding to $sim$2800 au at a distance of 2.16 kpc. These are the first astrometric measurements at 6.7 GHz in IRAS 19410+2336. The 22-GHz water maser line was imaged in 2005 and 2019 (the latter with good astrometry). Its velocities range from 13 to $sim$29 km s$^{-1}$. The peak flux density was found to be 18.7 Jy and 13.487 Jy in 2005, and 2019, respectively. The distribution of the water maser components is up to 165 mas, $sim$350 au at 2.16 kpc. We find that the Eastern methanol masers most probably trace outflows from the region of millimetre source mm1. The water masers to the West lie in a disc (flared or interacting with outflow/infall) around another more evolved millimetre source (13-s). The maser distribution suggests that the disc lies at an angle of 60$^{circ}$ or more to the plane of the sky and the observed line of sight velocities then suggest an enclosed mass between 44 M$_{odot}$ and as little as 11 M$_{odot}$ if the disc is edge-on. The Western methanol masers may be infalling.
We present a (sub)millimeter line survey of the methanol maser outflow located in the massive star-forming region DR21(OH) carried out with the Submillimeter Array (SMA) at 217/227 GHz and 337/347 GHz. We find transitions from several molecules towards the maser outflow such as CH$_3$OH, H$_2$CS, C$^{17}$O, H$^{13}$CO$^+$ and C$^{34}$S. However, with the present observations, we cannot discard the possibility that some of the observed species such as C$^{17}$O, C$^{34}$S, and H$_2$CS, might be instead associated with the compact and dusty continuum sources located in the MM2 region. Given that most of transitions correspond to methanol lines, we have computed a rotational diagram with CASSIS and a LTE synthetic spectra with XCLASS for the detected methanol lines in order to estimate the rotational temperature and column density in small solid angle of the outflow where enough lines are present. We obtain a rotational temperature of $28pm 2.5$K and a column density of $6.0pm 0.9 times 10^{15}$ cm$^{-2}$. These values are comparable to those column densities/rotational temperatures reported in outflows emanating from low-mass stars. Extreme and moderate physical conditions to excite the maser and thermal emission coexist within the CH$_3$OH flow. Finally, we do not detect any complex molecules associated with the flow, e.g., CH3OCHO, (CH3)2CO, and CH$_3$CH$_2$CN.
We present archival high angular resolution ($sim$ 2$$) $^{12}$CO(3-2) line and continuum submillimeter observations of the young stellar object HL Tau made with the Submillimeter Array (SMA). The $^{12}$CO(3-2) line observations reveal the presence of a compact and wide opening angle bipolar outflow with a northeast and southwest orientation (P.A. = 50$^circ$), and that is associated with the optical and infrared jet emanating from HL Tau with a similar orientation. On the other hand, the 850 $mu$m continuum emission observations exhibit a strong and compact source in the position of HL Tau that has a spatial size of $sim$ 200 $times$ 70 AU with a P.A. $=$ 145$^circ$, and a dust mass of around 0.1 M$_odot$. These physical parameters are in agreement with values obtained recently from millimeter observations. This submillimeter source is therefore related with the disk surrounding HL Tau.
We present the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the Cepheus A HW3d object. We measured for the first time relative proper motions of the H2O maser features, whose spatio-kinematics traces a compact bipolar outflow. This outflow looks highly collimated and expanding through ~ 280 AU (400 mas) at a mean velocity of ~ 21 km/s (~ 6 mas/yr) without taking into account the turbulent central maser cluster. The opening angle of the outflow is estimated to be ~ 30{circ}. The dynamical time-scale of the outflow is estimated to be ~ 100 years. Our results provide strong support that HW3d harbors an internal massive young star, and the observed outflow could be tracing a very early phase of star formation. We also have analyzed Very Large Array (VLA) archive data of 1.3 cm continuum emission obtained in 1995 and 2006 toward Cepheus A. The comparative result of the HW3d continuum emission suggests the possibility of the existence of distinct young stellar objects (YSOs) in HW3d and/or strong variability in one of their radio continuum emission components.
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