1,871 research outputs found
A Parallax-based Distance Estimator for Spiral Arm Sources
The spiral arms of the Milky Way are being accurately located for the first
time via trigonometric parallaxes of massive star forming regions with the
BeSSeL Survey, using the Very Long Baseline Array and the European VLBI
Network, and with the Japanese VERA project. Here we describe a computer
program that leverages these results to significantly improve the accuracy and
reliability of distance estimates to other sources that are known to follow
spiral structure. Using a Bayesian approach, sources are assigned to arms based
on their (l,b,v) coordinates with respect to arm signatures seen in CO and HI
surveys. A source's kinematic distance, displacement from the plane, and
proximity to individual parallax sources are also considered in generating a
full distance probability density function. Using this program to estimate
distances to large numbers of star forming regions, we generate a realistic
visualization of the Milky Way's spiral structure as seen from the northern
hemisphere.Comment: 25 pages with 16 figures; to appear in Ap
Trigonometric Parallaxes of Massive Star Forming Regions: G012.88+0.48 and W33
We report trigonometric parallaxes for water masers in the G012.88+0.48
region and in the massive star forming complex W33 (containing G012.68--0.18,
G012.81--0.19, G012.90--0.24, G012.90--0.26), from the Bar and Spiral Structure
Legacy (BeSSeL) survey using the Very Long Baseline Array. The parallax
distances to all these masers are consistent with kpc,
which locates the W33 complex and G012.88+0.48 in the Scutum spiral arm. Our
results show that W33 is a single star forming complex at about two-thirds the
kinematic distance of 3.7 kpc. The luminosity and mass of this region, based on
the kinematic distance, have therefore been overestimated by more than a factor
of two. The spectral types in the star cluster in W33\,Main have to be changed
by 1.5 points to later types.Comment: 9 pages, 11 figures, 2 tables; accepted for publication at A&
Trigonometric Parallaxes of Massive Star-Forming Regions. IX. The Outer Arm in the First Quadrant
We report a trigonometric parallax measurement with the Very Long Baseline
Array for the water maser in the distant high-mass star-forming region
G75.30+1.32. This source has a heliocentric distance of 9.25+-0.45 kpc, which
places it in the Outer arm in the first Galactic quadrant. It lies 200 pc above
the Galactic plane and is associated with a substantial HI enhancement at the
border of a large molecular cloud. At a Galactocentric radius of 10.7 kpc,
G75.30+1.32 is in a region of the Galaxy where the disk is significantly warped
toward the North Galactic Pole. While the star-forming region has an
instantaneous Galactic orbit that is nearly circular, it displays a significant
motion of 18 km/s toward the Galactic plane. The present results, when combined
with two previous maser studies in the Outer arm, yield a pitch angle of about
12 degrees for a large section of the arm extending from the first quadrant to
the third.Comment: 19 pages, 5 figures, 4 tables, accepted by The Astrophysical Journa
The 3D inelastic analysis methods for hot section components
Advanced 3-D inelastic structural/stress analysis methods and solution strategies for more accurate and yet more cost-effective analysis of combustors, turbine blades, and vanes are being developed. The approach is to develop four different theories, one linear and three higher order with increasing complexities including embedded singularities. Progress in each area is reported
Did Egret Detect Distant Supernova Remnants?
It might be thought that supernova remnants (SNRs) more distant than a few
kiloparsec from Earth could not have been detected by the EGRET experiment.
This work analyzes the observational status of this statement in the light of
new CO studies of SNRs.Comment: Accepted for publication in Advances in Space Research, in High
Energy Studies of Supernova Remnants and Neutron Stars, eds. W. Becker and W.
Hermsen (2003
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