5 research outputs found
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
Distance to Orion KL Measured with VERA
We present the initial results of multi-epoch VLBI observations of the 22 GHz
H2O masers in the Orion KL region with VERA (VLBI Exploration of Radio
Astrometry). With the VERA dual-beam receiving system, we have carried out
phase-referencing VLBI astrometry and successfully detected an annual parallax
of Orion KL to be 2.29+/-0.10 mas, corresponding to the distance of 437+/-19 pc
from the Sun. The distance to Orion KL is determined for the first time with
the annual parallax method in these observations. Although this value is
consistent with that of the previously reported, 480+/-80 pc, which is
estimated from the statistical parallax method using proper motions and radial
velocities of the H2O maser features, our new results provide the much more
accurate value with an uncertainty of only 4%. In addition to the annual
parallax, we have detected an absolute proper motion of the maser feature,
suggesting an outflow motion powered by the radio source I along with the
systematic motion of source I itself.Comment: 7 pages, 3 figures. PASJ, in press (Vol. 59, No. 5, October 25, 2007
issue
Absolute Proper Motions of H2O Masers Away from the Galactic Plane Measured with VERA in the "Superbubble" Region NGC 281
We report on absolute proper-motion measurements of an H2O maser source in
the NGC 281 West molecular cloud, which is located ~320 pc above the Galactic
plane and is associated with an HI loop extending from the Galactic plane. We
have conducted multi-epoch phase-referencing observations of the maser source
with VERA (VLBI Exploration of Radio Astrometry) over a monitoring period of 6
months since May 2006. We find that the H2O maser features in NGC 281 West are
systematically moving toward the southwest and further away from the Galactic
plane with a vertical velocity of ~20-30 km/s at its estimated distance of
2.2-3.5 kpc. Our new results provide the most direct evidence that the gas in
the NGC 281 region on the HI loop was blown out from the Galactic plane, most
likely in a superbubble driven by multiple or sequential supernova explosions
in the Galactic plane.Comment: 10 pages, 5 figures, PASJ in press (Vol. 59, No. 4; August 25, 2007
issue