11 research outputs found
Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry
We compare the parallaxes of stars from VLBI astrometry in the literature to
those in the Gaia DR2 catalog. Our full sample contains young stellar objects,
evolved AGB stars, pulsars and other radio stars. Excluding AGB stars, which
show significant discrepancies between Gaia and VLBI parallaxes, and stars in
binary systems, we obtain an average, systematic, parallax offset of as for Gaia DR2, consistent with their estimate of a parallax zero-point
between and 0 as.Comment: Accepted by Ap
The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration
We report astrometric results of VLBI phase-referencing observations of 22
GHz \hho\ masers emission toward the red hypergiant \vxsgr, one of most massive
and luminous red hypergiant stars in our Galaxy, using the Very Long Baseline
Array. A background source, \Jtwoze, projected 4\d4 from the target \vxsgr, was
used as the phase reference. For the low declinations of these sources, such a
large separation normally would seriously degrade the relative astrometry. We
use a two-step method of tropospheric delay calibration, which combines the
VLBI geodetic-block (or GPS) calibration with an image-optimization
calibration, to obtain a trigonometric parallax of mas,
corresponding to a distance of 1.56 kpc. The measured proper
motion of \vxsgr\ is and \masy\ in the eastward
and northward directions. The parallax and proper motion confirms that \vxsgr\
belong to the Sgr OB1 association. Rescaling bolometric luminosities in the
literature to our parallax distance, we find the luminosity of \vxsgr~is \Lsun, where the uncertainty is dominated by differing
photometry measurements.Comment: 16 pages, 10 figures, accepted by Ap
VLBI Astrometry of Radio Stars to Link Radio and Optical Celestial Reference Frames. I. HD 199178 AR Lacertae
To accurately link the radio and optical Celestial Reference Frames (CRFs) at
optical bright end, i.e., with Gaia G band magnitude < 13, increasing number
and improving sky distribution of radio stars with accurate astrometric
parameters from both Very Long Baseline Interferometry (VLBI) and Gaia
measurements are mandatory. We selected two radio stars HD 199178 and AR
Lacertae as the target for a pilot program for the frame link, using the Very
Long Baseline Array (VLBA) at 15 GHz at six epochs spanning about 1 year, to
measure their astrometric parameters. The measured parallax of HD 199178 is
mas and the proper motion is , , while the parallax of
AR Lac is mas and the proper motion is , . Our
VLBI measured astrometric parameters have accuracies about 4-5 times better
than the corresponding historic VLBI measurements and comparable accuracies
with those from Gaia, validating the feasibility of frame link using radio
stars. With the updated astrometric parameters for these two stars, there is a
25% reduction of the uncertainties on the Y axis for both orientation and spin
parameters.Comment: 11 pages, accepted by MNRAS on 2023 April 2
The parallax and 3D kinematics of water masers in the massive star-forming region G034.43+0.24
We report a trigonometric parallax measurement of 22 GHz water masers in the
massive star-forming region G034.43+0.24 as part of the Bar and Spiral
Structure Legacy (BeSSeL) Survey using the Very Long Baseline Array. The
parallax is 0.33050.018 mas, corresponding to a distance of
kpc. This locates G034.43+0.24 near the inner edge of
the Sagittarius spiral arm and at one end of a linear distribution of massive
young stars which cross nearly the full width of the arm. The measured
3-dimensional motion of G034.43+0.24 indicates a near-circular Galactic orbit.
The water masers display arc-like distributions, possibly bow shocks,
associated with winds from one or more massive young stars
VLBI astrometry on the white dwarf pulsar AR Scorpii
AR Scorpii (AR Sco), the only-known radio-pulsing white dwarf binary, shows unusual pulsating emission at the radio, infrared, optical, and ultraviolet bands. To determine its astrometric parameters at the radio band independently, we conducted multi-epoch Very Long Baseline Interferometry (VLBI) phase-referencing observations with the European VLBI Network at 5 GHz and the Chinese VLBI Network plus the Warkworth 30-m telescope (New Zealand) at 8.6 GHz. By using the differential VLBI astrometry, we provide high-precision astrometric measurements on the parallax (pi = 8.52(-0.07)(+0.04) mas) and proper motion (mu(alpha) = 9.48(-0.07)(+0.04) mas yr(-1), mu(delta) = -51.32(-0.38)(+0.22) mas yr (-1)). The new VLBI results agree with the optical Gaia astrometry. Our kinematic analysis reveals that the Galactic space velocities of AR Sco are quite consistent with that of both intermediate polars and polars. Combined with the previous tightest VLBI constraint on the size, our parallax distance suggests that the radio emission of AR Sco should be located within the light cylinder of its white dwarf
EAVN Astrometry toward the Extreme Outer Galaxy: Kinematic distance with the proper motion of G034.84-00.95
We aim to reveal the structure and kinematics of the Outer-Scutum-Centaurus
(OSC) arm located on the far side of the Milky Way through very long baseline
interferometry (VLBI) astrometry using KaVA, which is composed of KVN (Korean
VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the
proper motion of a 22 GHz HO maser source, which is associated with the
star-forming region G034.8400.95, to be (,
) = (1.610.18, 4.290.16) mas yr in
equatorial coordinates (J2000). We estimate the 2D kinematic distance to the
source to be 18.61.0 kpc, which is derived from the variance-weighted
average of kinematic distances with LSR velocity and the Galactic-longitude
component of the measured proper motion. Our result places the source in the
OSC arm and implies that G034.8400.95 is moving away from the Galactic plane
with a vertical velocity of 3816 km s. Since the H I supershell
GS033+0649 is located at a kinematic distance roughly equal to that of
G034.8400.95, it is expected that gas circulation occurs between the outer
Galactic disk around G034.8400.95 with a Galactocentric distance of
12.8 kpc and halo. We evaluate possible origins of the fast
vertical motion of G034.8400.95, which are (1) supernova explosions and (2)
cloud collisions with the Galactic disk. However, neither of the possibilities
are matched with the results of VLBI astrometry as well as spatial
distributions of H II regions and H I gas.Comment: Accepted for publication in PASJ. 14 figures; 8 table