33 research outputs found
Rotating and infalling motion around the high-mass young stellar object Cepheus A-HW2 observed with the methanol maser at 6.7 GHz
We have measured the internal proper motions of the 6.7 GHz methanol masers
associated with Cepheus A (Cep A) HW2 using Very Long Baseline Interferometery
(VLBI) observations. We conducted three epochs of VLBI monitoring observations
of the 6.7 GHz methanol masers in Cep A-HW2 with the Japanese VLBI Network
(JVN) over the period between 2006-2008. In 2006, we were able to use
phase-referencing to measure the absolute coordinates of the maser emission
with an accuracy of a few milliarcseconds. We compared the maser distribution
with other molecular line observations that trace the rotating disk. We
measured the internal proper motions for 29 methanol maser spots, of which 19
were identified at all three epochs and the remaining ten at only two epochs.
The magnitude of proper motions ranged from 0.2 to 7.4 km/s, with an average of
3.1 km/s. Although there are large uncertainties in the observed internal
proper motions of the methanol maser spots in Cep A, they are well fitted by a
disk that includes both rotation and infall velocity components. The derived
rotation and infall velocities at the disk radius of 680 au are 0.5 +- 0.7 and
1.8 +- 0.7 km/s, respectively. Assuming that the modeled disk motion accurately
represents the accretion disk around the Cep A-HW2 high-mass YSO, we estimated
the mass infall rate to be 3 x 10^{-4} n_8 Msun/yr (n_8 is the gas volume
density in units of 10^{8} cm^{-3}). The combination of the estimated mass
infall rate and the magnitude of the fitted infall velocity suggests that Cep
A-HW2 is at an evolutionary phase of active gas accretion from the disk onto
the central high-mass YSO. The infall momentum rate is estimated to be 5 x
10^{-4} n_8 Msun/yr km/s, which is larger than the estimated stellar radiation
pressure of the HW2 object, supporting the hypothesis that this object is in an
active gas accretion phase.Comment: 16 pages, 6 figures, 5 tables, accepted for publication in Astronomy
& Astrophysic
Intermittent maser flare around the high mass young stellar object G353.273+0.641 I: data & overview
We have performed VLBI and single-dish monitoring of 22 GHz HO maser
emission from the high mass young stellar object G353.273+0.641 with VERA (VLBI
Exploration of Radio Astrometry) and Tomakamai 11-m radio telescope. Two maser
flares have been detected, separated almost two years. Frequent VLBI monitoring
has revealed that these flare activities have been accompanied by structural
change of the prominent shock front traced by H2O maser alignments. We have
detected only blue-shifted emissions and all maser features have been
distributed within very small area of 200 200 au in spite of
wide velocity range (> 100 km s). The light curve shows notably
intermittent variation and suggests that the HO masers in G353.273+0.641
are excited by episodic radio jet. The time-scale of \sim2 yr and
characteristic velocity of \sim500 km s also support this
interpretation. Two isolated velocity components of C50 (-53 \pm 7 km s)
and C70 (-73 \pm 7 km s) have shown synchronised linear acceleration of
the flux weighted V_{\rmn{LSR}} values (\sim-5 km s yr) during
the flare phase. This can be converted to the lower-limit momentum rate of 1.1
\times 10 M_{\sun} km s yr. Maser properties are quite
similar to that of IRAS 20126+4104 especially. This corroborates the previous
suggestion that G353.273+0.641 is a candidate of high mass protostellar object.
The possible pole-on geometry of disc-jet system can be suitable for direct
imaging of the accretion disc in this case.Comment: 13 pages, 5 figures accepted for publication in MNRA
Microstructure and kinematics of H2O masers in the massive star forming region IRAS 06061+2151
We have made multi-epoch VLBI observations of H2O maser emission in the
massive star forming region IRAS 06061+2151 with the Japanese VLBI network
(JVN) from 2005 May to 2007 October. The detected maser features are
distributed within an 1\arcsec1\arcsec (2000 au2000 au at the
source position) around the ultra-compact H {\small\bf II} region seen in radio
continuum emission. Their bipolar morphology and expanding motion traced
through their relative proper motions indicate that they are excited by an
energetic bipolar outflow. Our three-dimensional model fitting has shown that
the maser kinematical structure in IRAS 06061+2151 is able to be explained by a
biconical outflow with a large opening angle ( 50\degr). The position angle
of the flow major axis coincides very well with that of the large scale jet
seen in 2.1\:\mu\rmn{m} hydrogen emission. This maser geometry indicates the
existence of dual structures composed of a collimated jet and a less collimated
massive molecular flow. We have also detected a large velocity gradient in the
southern maser group. This can be explained by a very small (on a scale of
several tens of au) and clumpy (the density contrast by an order of magnitude
or more) structure of the parental cloud. Such a structure may be formed by
strong instability of shock front or splitting of high density core.Comment: 14 pages, 6 figures accepted for publication in MNRA
British television news in the 1990s Newsworthiness in a multi-organisational and multi-programme environment
SIGLEAvailable from British Library Document Supply Centre-DSC:DXN014458 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
New Detection of an Extremely Blue-shift Dominated Jet in G353.273+0.641: A Possible Disk-Jet System on 100 AU Scale
We report a new detection of an unusual molecular jet from a high mass protostellar object G353.273+0.641 using the NRO 45m telescope. Newly detected SiO (υ = 0, J = 2-1) jet shows highly blue-shift dominated spectrum similar to the associated 22 GHz maser emission. The remarkable blue-shift dominance in both of the maser and SiO emission can be caused by a compact (< 170 AU) and optically thick face-on disk, masking the red-shifted part of the jet