36 research outputs found
VERA Geodetic Activities
This report briefly describes the geodetic activities of VERA in the year 2012. The regular geodetic observations are carried out both in K- and S/X-bands. The frequency of regular observations is three times a month-twice for the VERA internal observations in K-band. The networks of the S/X sessions are JADE of GSI and IVS-T2. The raw data of the T2 and JADE sessions are electronically transferred to the Bonn, Haystack, and GSI correlators via Internet. Gravimetric observations are carried out at the VERA stations. An SG was installed at Mizusawa and placed in the vicinity of the VERA antenna in order to monitor vertical displacement at the end of 2008, and the observations continued throughout the year. Also at the VERA-Ishigakijima station, continuous operation of the SG started in 2012. The crustal movements generated by the 2011 earthquake off the Pacific coast of Tohoku continued during 2012, and displacement of the VERA-Mizusawa position by post-seismic creeping continued
The first year of Antarctic VLBI observations
We are undertaking a series of geodetic VLBI observations between the Syowa Station 11-m antenna in Antarctica, and the 26-m antennas in Hobart Tasmania and Hartebeesthoek South Africa. These observations are the beginning of our campaign to monitor the motion and stability of the Antarctic plate. We describe here the results of the first year\u27s observations made during the southern summer and winter of 1998. Two mutually incompatible recording systems, K4 and S2, are used. The Mitaka FX Correlator was used to correlate these data. By using software called CALC3/MSOLV, the mean position of the antenna\u27s geodetic reference point was found to be X=1766194.152±0.006m, Y=1460410.923±0.005m and Z=- 5932273.329±0.015m at the epoch of 1998.9 in the International Terrestrial Reference Frame 2000 (ITRF2000) system. From a comparison with measurements made with other space geodetic techniques we estimate that our results have typical uncertainties of no more than 2 to 3cm in each coordinate
Multifrequency VLBI Observations of the Broad Absorption Line Quasar J1020+4320: Recently Restarted Jet Activity?
This paper reports very-long-baseline interferometry observations of the
radio-loud broad absorption line (BAL) quasar J1020+4320 at 1.7, 2.3, 6.7, and
8.4 GHz using the Japanese VLBI network (JVN) and European VLBI network (EVN).
The radio morphology is compact with a size of ~10 pc. The convex radio
spectrum is stable over the last decade; an observed peak frequency of 3.2 GHz
is equivalent to 9.5 GHz in the rest frame, suggesting an age of the order of
~100 years as a radio source, according to an observed correlation between
linear size and peak frequency of compact steep spectrum (CSS) and giga-hertz
peaked spectrum (GPS) radio sources. A low-frequency radio excess suggests
relic of past jet activity. J1020+4320 may be one of the quasars with recurrent
and short-lived jet activity during a BAL-outflowing phase.Comment: 7 pages, 2 figures, 2 tables, accepted for publication in PAS
Astrometry of Water Maser Sources in Nearby Molecular Clouds with VERA - II. SVS 13 in NGC 1333
We report on the results of multi-epoch VLBI observations with VERA (VLBI
Exploration of Radio Astrometry) of the 22 GHz H2O masers associated with the
young stellar object SVS 13 in the NGC 1333 region. We have carried out
phase-referencing VLBI astrometry and measured an annual parallax of the maser
features in SVS 13 of 4.25+/-0.32 mas, corresponding to the distance of
235+/-18 pc from the Sun. Our result is consistent with a photometric distance
of 220 pc previously reported. Even though the maser features were detectable
only for 6 months, the present results provide the distance to NGC 1333 with
much higher accuracy than photometric methods. The absolute positions and
proper motions have been derived, revealing that the H2O masers with the LSR
(local standard of rest) velocities of 7-8 km s-1 are most likely associated
with VLA4A, which is a radio counterpart of SVS 13. The origin of the observed
proper motions of the maser features are currently difficult to attribute to
either the jet or the rotating circumstellar disk associated with VLA4A, which
should be investigated through future high-resolution astrometric observations
of VLA4A and other radio sources in NGC 1333.Comment: 9 pages, 5 figures. PASJ, in press (2008, Vol. 60, No. 1
Astrometric VLBI observations of HO masers in an extreme OH/IR star candidate NSV17351
Results of astrometric very long baseline interferometry (VLBI) observations
towards an extreme OH/IR star candidate NSV17351 are presented. We used the
VERA (VLBI Exploration of Radio Astrometry) VLBI array to observe 22\,GHz
HO masers of NSV17351. We derived an annual parallax of 0.2470.035 mas
which corresponds to a distance of 4.050.59 kpc. By averaging the proper
motions of 15 maser spots, we obtained the systemic proper motion of NSV17351
to be () (1.19
0.11, 1.30 0.19) mas\,yr. The maser spots spread out over a
region of 20 mas 30 mas, which can be converted to a spatial
distribution of 80 au 120 au at the source distance.
Internal motions of the maser spots suggest an outward moving maser region with
respect to the estimated position of the central star. From single dish
monitoring of the HO maser emission, we estimate the pulsation period of
NSV17351 to be 112224 days. This is the first report of the periodic
activity of NSV17351, indicating that NSV17351 could have a mass of
4\,M. We confirmed that the time variation of HO masers can
be used as a period estimator of variable OH/IR stars. Furthermore, by
inspecting dozens of double-peaked HO maser spectra from the last 40 years,
we detected a long-term acceleration in the radial velocity of the
circumstellar matter to be km\,s\,yr Finally, we
determined the position and kinematics of NSV17351 in the Milky Way Galaxy and
found that NSV17351 is located in an interarm region between the Outer and
Perseus arms. We note that astrometric VLBI observations towards extreme OH/IR
stars are useful samples for studies of the Galactic dynamics.Comment: Published in the Publications of the Astronomical Society of Japa
Astrometry of Galactic Star Forming Region Sharpless 269 with VERA : Parallax Measurements and Constraint on Outer Rotation Curve
We have performed high-precision astrometry of H2O maser sources in Galactic
star forming region Sharpless 269 (S269) with VERA. We have successfully
detected a trigonometric parallax of 189+/-8 micro-arcsec, corresponding to the
source distance of 5.28 +0.24/-0.22 kpc. This is the smallest parallax ever
measured, and the first one detected beyond 5 kpc. The source distance as well
as proper motions are used to constrain the outer rotation curve of the Galaxy,
demonstrating that the difference of rotation velocities at the Sun and at S269
(which is 13.1 kpc away from the Galaxy's center) is less than 3%. This gives
the strongest constraint on the flatness of the outer rotation curve and
provides a direct confirmation on the existence of large amount of dark matter
in the Galaxy's outer disk.Comment: 7 pages and 4 figures, Accepted by PASJ (Vol. 59, No. 5, October 25,
2007 issue
Fundamental Parameters of the Milky Way Galaxy Based on VLBI astrometry
We present analyses to determine the fundamental parameters of the Galaxy
based on VLBI astrometry of 52 Galactic maser sources obtained with VERA, VLBA
and EVN. We model the Galaxy's structure with a set of parameters including the
Galaxy center distance R_0, the angular rotation velocity at the LSR Omega_0,
mean peculiar motion of the sources with respect to Galactic rotation (U_src,
V_src, W_src), rotation-curve shape index, and the V component of the Solar
peculiar motions V_sun. Based on a Markov chain Monte Carlo method, we find
that the Galaxy center distance is constrained at a 5% level to be R_0 = 8.05
+/- 0.45 kpc, where the error bar includes both statistical and systematic
errors. We also find that the two components of the source peculiar motion
U_src and W_src are fairly small compared to the Galactic rotation velocity,
being U_src = 1.0 +/- 1.5 km/s and W_src = -1.4 +/- 1.2 km/s. Also, the
rotation curve shape is found to be basically flat between Galacto-centric
radii of 4 and 13 kpc. On the other hand, we find a linear relation between
V_src and V_sun as V_src = V_sun -19 (+/- 2) km/s, suggesting that the value of
V_src is fully dependent on the adopted value of V_sun. Regarding the rotation
speed in the vicinity of the Sun, we also find a strong correlation between
Omega_0 and V_sun. We find that the angular velocity of the Sun, Omega_sun,
which is defined as Omega_sun = Omega_0 + V_sun/R_0, can be well constrained
with the best estimate of Omega_sun = 31.09 +/- 0.78 km/s/kpc. This corresponds
to Theta_0 = 238 +/- 14 km/s if one adopts the above value of R_0 and recent
determination of V_sun ~ 12 km/s.Comment: 14 pages, 6 figures, PASJ in pres