56 research outputs found
Absolute Proper Motion of IRAS 00259+5625 with VERA : Indication of Superbubble Expansion Motion
We present the first measurement of the absolute proper motions of IRAS
00259+5625 (CB3, LBN594) associated with the HI loop called the "NGC281
superbubble" that extends from the Galactic plane over ~300 pc toward
decreasing galactic latitude. The proper motion components measured with VERA
are (mu_alpha cos(delta), mu_delta) = (-2.48 +/- 0.32, -2.85 +/- 0.65) mas
yr^{-1}, converted into (mu_l cos(b), mu_b) = (-2.72 +/- 0.32, -2.62 +/- 0.65)
mas yr^{-1} in the Galactic coordinates. The measured proper motion
perpendicular to the Galactic plane (mu_b) shows vertical motion away from the
Galactic plane with a significance of about ~4-sigma. As for the source
distance, the distance measured with VERA is marginal, 2.4^{+1.0}_{-0.6} kpc.
Using the distance, an absolute vertical motion (v_{b}) of -17.9 +/- 12.2 km
s^{-1} is determined with ~1.5-sigma significance. The tendency of the large
vertical motion is consistent with previous VLBI results for NGC 281 associated
with the same superbubble. Thus, our VLBI results indicate the superbubble
expansion motion whose origin is believed to be sequential supernova
explosions.Comment: 12 pages, 5 figures, accepted for publication in PASJ (Vol. 66, No.
1
Parallax of a Mira variable R Ursae Majoris studied with astrometric VLBI
We have measured an annual parallax of the Mira variable R~Ursae~Majoris
(R~UMa) with the VLBI exploration for Radio Astronomy (VERA). From the
monitoring VLBI observations spanning about two years, we detected HO maser
spots in the LSR velocities ranges from 37 to 42 km\,s. We derived an
annual parallax of 1.970.05\,mas, and it gives a corresponding distance of
50813\,pc. The VLBI maps revealed 72 maser spots distributed in 110
au area around an expected stellar position. Circumstellar kinematics of the
maser spots were also revealed by subtracting a systemic motion in the
Hipparcos catalog from proper motions of each maser spots derived from our VLBI
observations. Infrared photometry is also conducted to measure a band
apparent magnitude, and we obtained a mean magnitude of =
1.190.02\,mag. Using the trigonometric distance, the is converted to
a band absolute magnitude of 7.340.06\,mag. This result gives
a much more accurate absolute magnitude of R~UMa than previously provided. We
solved a zero-point of relation for the Galactic Mira variables
and obtained a relation of 3.52 + (1.09 0.14). Other
long period variables including red supergiants, whose distances were
determined from astrometric VLBI, were also compiled to explore the different
sequences of relation.Comment: 9 figur
Distance to G14.33-0.64 in the Sagittarius Spiral Arm: H2O Maser Trigonometric Parallax with VERA
We report on trigonometric parallax measurements for the Galactic star
forming region G14.33-0.64 toward the Sagittarius spiral arm. We conducted
multi-epoch phase-referencing observations of an H2O maser source in
G14.33-0.64 with the Japanese VLBI array VERA. We successfully detected a
parallax of 0.893+/-0.101 mas, corresponding to a source distance of
1.12+/-0.13 kpc, which is less than half of the kinematic distance for
G14.33-0.64. Our new distance measurement demonstrates that the Sagittarius arm
lies at a closer distance of ~1 kpc, instead of previously assumed ~2-3 kpc
from kinematic distances. The previously suggested deviation of the Sagittarius
arm toward the Galactic center from the symmetrically fitted model (Taylor &
Cordes 1993) is likely due to large errors of kinematic distances at low
galactic longitudes. G14.33-0.64 most likely traces the near side of the
Sagittarius arm. We attempted fitting the pitch angle of the arm with other
parallax measurements along the arm, which yielded two possible pitch angles of
i=34.7+/-2.7 degrees and i=11.2+/-10.5 degrees. Our proper motion measurements
suggest G14.33-0.64 has no significant peculiar motion relative to the
differential rotation of the Galaxy (assumed to be in a circular orbit),
indicating that the source motion is in good agreement with the Galactic
rotation.Comment: 14 pages, 7 figures, to appear in PASJ Vol. 62, No.
Accurate Parallax Measurement toward the Symbiotic Star R Aquarii
Multi-epoch phase-referencing VLBI (Very Long Baseline Interferometry)
observations with VERA (VLBI Exploration of Radio Astrometry) were performed
for the symbiotic star R Aquarii (R Aqr) from September 2005 to Oct 2006.
Tracing one of the , SiO maser spots, we measured an annual
parallax of mas, corresponding to a distance of
pc. Our result is consistent with earlier distance
measurements, but yields the highest accuracy of about level. Applying
our distance, we derived an absolute K-band magnitude of , which is consistent with the recent Period-Luminosity relation
by VLBI parallax measurements for 5 OH-Mira variables. In addition, the
expansion age of an inner nebulae around R Aqr is found to be about 240 years,
corresponds to about the year 1773.Comment: 7 pages, 3 figures, 1 table, Accepted for publication in PAS
Outer Rotation Curve of the Galaxy with VERA III: Astrometry of IRAS 07427-2400 and Test of the Density-Wave Theory
We report the trigonometric parallax of IRAS 07427-2400 with VERA to be 0.185
0.027 mas, corresponding to a distance of 5.41 kpc. The
result is consistent with the previous result of 5.32 kpc
obtained by Choi et al. (2014) within error. To remove the effect of internal
maser motions (e.g., random motions), we observed six maser features associated
with IRAS 07427-2400 and determined systematic proper motions of the source by
averaging proper motions of the six maser features. The obtained proper motions
are (cos, ) = (1.79 0.32, 2.60
0.17) mas yr in equatorial coordinates, while Choi et al. (2014)
showed (cos, ) = (2.43 0.02, 2.49
0.09) mas yr with one maser feature. Our astrometry results place
the source in the Perseus arm, the nearest main arm in the Milky Way. Using our
result with previous astrometry results obtained from observations of the
Perseus arm, we conducted direct (quantitative) comparisons between 27
astrometry results and an analytic gas dynamics model based on the density-wave
theory and obtained two results. First is the pitch angle of the Perseus arm
determined by VLBI astrometry, 11.1 1.4 deg, differing from what is
determined by the spiral potential model (probably traced by stars), 20
deg. The second is an offset between a dense gas region and the bottom of the
spiral potential model. The dense gas region traced by VLBI astrometry is
located downstream of the spiral potential model, which was previously
confirmed in the nearby grand-design spiral galaxy M51 in Egusa et al. (2011).Comment: 28 pages, 11 figures, accepted for publication in PAS
Annual parallax measurement of a Mira variable star BX Cam with VERA
We report results of astrometric VLBI observations toward a Mira variable
star BX~Cam using the VLBI array "VERA". The observations were performed from
February 2012 to November 2014. Obtained parallax is 1.730.03 mas
corresponding to a distance of 0.580.01 kpc. Parallax of this source was
also reported in Gaia DR2 as 4.130.25 mas, and there is a 240 \%
difference between these two measurements. Astrometric results from our VLBI
observations show that we exactly traced angular motions of the seven maser
spots in BX~Cam. We calculated stellar luminosities using both parallaxes, and
obtained luminosities of and
. Deduced luminosities also
support a validity of the parallax that we determined with VERA. Evaluating the
two parallaxes, we concluded that the parallax of 1.730.03 mas from the
VERA observations is correct for BX~Cam. We obtained a systemic motion of
BX~Cam as (,
) (13.480.14, 34.300.18)
mas\,yr. A total of 73 HO maser spots detected from our VLBI
observations show a spatial distribution of 30 au 80 au with a strong
elongation along north-south direction. They show outflows with a
three-dimensional velocity of 14.791.40 km\,s. From a comparison
between time variations of -band magnitudes and HO maser, we found that
variation of the HO maser is relevant to that seen in -band even though
the HO maser does not recover its maximum flux in each cycle.Comment: 10 pages, 6 figures, 5 tables, Accepted by PAS
VLBI Astrometry of AGB Variables with VERA -- A Mira Type Variable T Lepus
We conducted phase referencing VLBI observations of the Mira variable T~Lepus
(T~Lep) using VERA, from 2003 to 2006. The distance to the source was
determined from its annual parallax which was measured to be 3.060.04 mas,
corresponding to a distance of 3274\,pc. Our observations revealed the
distribution and internal kinematics of HO masers in T~Lep, and we derived
a source systemic motions of 14.600.50 mas yr and 35.430.79
mas yr in right ascension and declination, respectively. We also
determined a LSR velocity of 27.63 km s.
Comparison of our result with an image recently obtained from the VLTI infrared
interferometer reveals a linear scale picture of the circumstellar structure of
T~Lep. Analysis of the source systemic motion in the Galacto-centric coordinate
frame indicates a large peculiar motion, which is consistent with the general
characteristics of AGB stars. This source makes a contribution to the
calibration of the period-luminosity relation of Galactic Mira variables. From
the compilation of data for nearby Mira variables found in the literature,
whose distances were derived from astrometric VLBI observations, we have
calibrated the Galactic Mira period-luminosity relation to a high degree of
accuracy.Comment: 13 pages, 6 figures, accepted for publication in PAS
Outer Rotation Curve of the Galaxy with VERA I: Trigonometric parallax of IRAS 05168+3634
We report measurement of trigonometric parallax of IRAS 05168+3634 with VERA.
The parallax is 0.532 +/- 0.053 mas, corresponding to a distance of
1.88+0.21/-0.17 kpc. This result is significantly smaller than the previous
distance estimate of 6 kpc based on kinematic distance. This drastic change in
the source distance revises not only physical parameters of IRAS 05168+3634,
but also its location of the source, placing it in the Perseus arm rather than
the Outer arm. We also measure proper motions of the source. A combination of
the distance and the proper motions with systemic velocity yields rotation
velocity ({\Theta}) of 227+9/-11 km s-1 at the source, assuming {\Theta}0 = 240
km s-1. Our result combined with previous VLBI results for six sources in the
Perseus arm indicates that the sources rotate systematically slower than the
Galactic rotation velocity at the LSR. In fact, we show observed disk peculiar
motions averaged over the seven sources in the Perseus arm as (Umean, Vmean) =
(11 +/- 3, -17 +/- 3) km s-1, indicating that these seven sources are
systematically moving toward the Galactic center, and lag behind the Galactic
rotation.Comment: 11 pages, 4 figures and 6 tables, accepted for the publication in
PAS
Positional Coincidence of H2O Maser and a Plasma Obscuring Torus in Radio Galaxy NGC 1052
We present multi-frequency simultaneous VLBA observations at 15, 22 and 43
GHz towards the nucleus of the nearby radio galaxy NGC 1052. These three
continuum images reveal a double-sided jet structure, whose relative intensity
ratios imply that the jet axis is oriented close to the sky plane. The steeply
rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest
that synchrotron emission is absorbed by foreground thermal plasma. We detected
H2O maser emission in the velocity range of 1550-1850 km/s, which is redshifted
by 50-350 km/s with respect to the systemic velocity of NGC 1052. The
redshifted maser gas appears projected against both sides of the jet, in the
same manner as the HI seen in absorption. The H2O maser gas are located where
the free-free absorption opacity is large. This probably imply that the masers
in NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus
of NGC 4258. Such circumnuclear structure can be the sence of accreting onto
the central engine.Comment: 18 pages, 7 figures, accepted for publication in Ap
Software Polarization Spectrometer "PolariS"
We have developed a software-based polarization spectrometer, PolariS, to
acquire full-Stokes spectra with a very high spectral resolution of 61 Hz. The
primary aim of PolariS is to measure the magnetic fields in dense star-forming
cores by detecting the Zeeman splitting of molecular emission lines. The
spectrometer consists of a commercially available digital sampler and a Linux
computer. The computer is equipped with a graphics processing unit (GPU) to
process FFT and cross-correlation using the CUDA (Compute Unified Device
Architecture) library developed by NVIDIA. Thanks to a high degree of precision
in quantization of the analog-to-digital converter and arithmetic in the GPU,
PolariS offers excellent performances in linearity, dynamic range, sensitivity,
bandpass flatness and stability. The software has been released under the MIT
License and is available to the public. In this paper, we report the design of
PolariS and its performance verified through engineering tests and
commissioning observations.Comment: 18 pages, 14 figures, Accepted for Journal of Astronomical
Instrumentatio
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