621 research outputs found
Galactic Structure and Radioactivity Source Distributions
A probable sky map of the emission from a short-lived isotrope produced by
massive stars is presented. The model is based on the nonaxisymmetric component
of a dust distribution model developed to reproduce Galactic FIR emission.
Features seen in COMPTEL observations are qualitatively reproduced.Comment: 6 pages w/ 4 figures, invited conference paper for "Radioactivities
in Astronomy" to be published in New Astronom
A three-dimensional Galactic extinction model
A large-scale three-dimensional model of Galactic extinction is presented
based on the Galactic dust distribution model of Drimmel and Spergel (2001).
The extinction A_V to any point within the Galactic disk can be quickly deduced
using a set of three-dimensional cartesian grids. Extinctions from the model
are compared to empirical extinction measures, including lines-of-sight in and
near the Galactic plane using optical and NIR extinction measures; in
particular we show how extinction can be derived from NIR color-magnitude
diagrams in the Galactic plane to a distance of 8 kiloparsec.Comment: 12 pages, to be published in A&
A self-consistent model of Galactic stellar and dust infrared emission and the abundance of polycyclic aromatic hydrocarbons
We present a self-consistent three-dimensional Monte-Carlo radiative transfer
model of the stellar and dust emission in the Milky-Way, and have computed
synthetic observations of the 3.6 to 100 microns emission in the Galactic
mid-plane. In order to compare the model to observations, we use the GLIMPSE,
MIPSGAL, and IRAS surveys to construct total emission spectra, as well as
longitude and latitude profiles for the emission. The distribution of stars and
dust is taken from the SKY model, and the dust emissivities includes an
approximation of the emission from polycyclic aromatic hydrocarbons in addition
to thermal emission. The model emission is in broad agreement with the
observations, but a few modifications are needed to obtain a good fit. Firstly,
by adjusting the model to include two major and two minor spiral arms rather
than four equal spiral arms, the fit to the longitude profiles for |l|>30
degrees can be improved. Secondly, introducing a deficit in the dust
distribution in the inner Galaxy results in a better fit to the shape of the
IRAS longitude profiles at 60 and 100 microns. With these modifications, the
model fits the observed profiles well, although it systematically
under-estimates the 5.8 and 8.0 microns fluxes. One way to resolve this
discrepancy is to increase the abundance of PAH molecules by 50% compared to
the original model, although we note that changes to the dust distribution or
radiation field may provide alternative solutions. Finally, we use the model to
quantify which stellar populations contribute the most to the heating of
different dust types, and which stellar populations and dust types contribute
the most to the emission at different wavelengths.Comment: Published in A&A. This version has been revised (compared to the
published version) to include additional references to previous work. Scripts
to reproduce the results in this paper can be found as supplementary material
on the A&A site, or at https://github.com/hyperion-rt/paper-galaxy-rt-mode
Evidence for orbital motion of CW Leonis from ground-based astrometry
© 2017 The Authors.Recent Atacama Large Millimeter/submillimeter Array (ALMA) observations indicate that CW Leo, the closest carbon-rich asymptotic giant branch star to Sun, might have a low-mass stellar companion. We present archival ground-based astrometric measurements of CW Leo obtained within the context of the Torino Parallax Program and with > 6 yr (1995-2001) of time baseline. The residuals to a single-star solution show significant curvature, and they are strongly correlatedwith thewell-known I-band photometric variations due to stellar pulsations. We describe successfully the astrometry of CW Leo with a variability-induced motion (VIM) + acceleration model. We obtain proper motion and parallax of the centre-of-mass of the binary, the former in fair agreement with recent estimates, the latter at the near end of the range of inferred distances based on indirect methods. The VIM + acceleration model results allow us to derive a companion mass in agreement with that inferred by ALMA, they point towards a somewhat longer period than implied by ALMA, but are not compatible with much longer period estimates. These data will constitute a fundamental contribution towards the full understanding of the orbital architecture of the system when combined with Gaia astrometry, providing an ~25 yr time baseline.Peer reviewe
A Molecular Spiral Arm in the Far Outer Galaxy
We have identified a spiral arm lying beyond the Outer Arm in the first
Galactic quadrant ~15 kpc from the Galactic center. After tracing the arm in
existing 21 cm surveys, we searched for molecular gas using the CfA 1.2 meter
telescope and detected CO at 10 of 220 positions. The detections are
distributed along the arm from l = 13 deg, v = -21 km/s to l = 55 deg, v = -84
km/s and coincide with most of the main H I concentrations. One of the
detections was fully mapped to reveal a large molecular cloud with a radius of
47 pc and a molecular mass of ~50,000 Mo. At a mean distance of 21 kpc, the
molecular gas in this arm is the most distant yet detected in the Milky Way.
The new arm appears to be the continuation of the Scutum-Centaurus Arm in the
outer Galaxy, as a symmetric counterpart of the nearby Perseus Arm.Comment: 11 pages, 4 figures, 1 Table, ApJ Letters, in pres
Kinematic response of the outer stellar disk to a central bar
We study, using direct orbit integrations, the kinematic response of the
outer stellar disk to the presence of a central bar, as in the Milky-Way. We
find that the bar's outer Lindblad resonance (OLR) causes significant
perturbations of the velocity moments. With increasing velocity dispersion, the
radius of these perturbations is shifted outwards, beyond the nominal position
of the OLR, but also the disk becomes less responsive. If we follow Dehnen
(2000) in assuming that the OLR occurs just inside the Solar circle and that
the Sun lags the bar major axis by ~20 degrees, we find (1) no significant
radial motion of the local standard of rest (LSR), (2) a vertex deviation of
\~10 degrees and (3) a lower ratio sigma_2/sigma_1 of the principal components
of the velocity- dispersion tensor than for an unperturbed disk. All of these
are actually consistent with the observations of the Solar-neighbourhood
kinematics. Thus it seems that at least the lowest-order deviations of the
local-disk kinematics from simple expectations based on axisymmetric
equilibrium can be attributed entirely to the influence of the Galactic bar.Comment: 10 pages, 8 figures, accepted for publication in A&
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