Issue |
A&A
Volume 458, Number 1, October IV 2006
|
|
---|---|---|
Page(s) | 151 - 162 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20054480 | |
Published online | 16 October 2006 |
The distribution of maser stars in the inner Milky Way: the effect of a weak, rotating bar
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands e-mail: habing@strw.leidenuniv.nl
Received:
5
November
2005
Accepted:
26
July
2006
We derive the distribution of maser stars in the inner
Milky Way based on an analysis of diagrams of longitude versus
line-of-sight-velocity (=lV-diagrams) for two samples of maser stars: 771
OH/IR stars and 363 SiO-maser stars. The stars are all close to
the plane of the Milky Way and have longitudes from
to
.
The two lV-diagrams are compared qualitatively and found to be very
similar. They also compare well with the lV-diagram of interstellar
CO, but there are significant differences in detail between the
stellar lV-diagrams and that of the ISM.
Based on the qualitative discussion we divide the lV-diagrams into
seven areas. In each area we count the number of stars as
observed and compare these numbers with those predicted by an
assumed set of orbits in a galactic potential. This potential is
axially symmetric but a weak rotating bar has been added. We
conclude that the maser stars move on almost circular orbits
outside of about 3.5 kpc, but that the orbits become more and
more elongated when one goes deep inside our MW. We find a strong
effect of the Corotation (=CR) resonance at 3.3 kpc, we see a
small but noticeable effect of the Outer Lindblad Resonance at
5 kpc and no effect of the Inner Lindblad Resonance (=ILR) at
kpc.
We find a set of 6 groups of orbits that together predict counts
in agreement with the counts of stars observed. We then calculate
the trajectory of each orbit and so find the distribution of the
maser stars in the plane of the MWG. This distribution has two
new (but not unexpected) features. The first is a bar-like
distribution within 2 kpc from the GC outlined. These orbits
explain the high-velocity stars near
in the forbidden
and the permitted quadrants. The second feature are two
“croissant”-like voids in the distribution close to the CR
radius (3.3 kpc). These voids are the consequence of the
presence of the co-rotation resonance. We find excellent agreement with an earlier reconstruction by
Sevenster (1999) based on partially the same data but on a
completely different analysis.
Key words: Galaxy: structure / stars: AGB and post-AGB / Galaxy: center
© ESO, 2006
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