Bibcode
DOI
López-Corredoira, M.; Garzón, F.; Beckman, J. E.; Mahoney, T. J.; Hammersley, P. L.; Calbet, X.
Bibliographical reference
The Astronomical Journal, Volume 118, Issue 1, pp. 381-389.
Advertised on:
7
1999
Citations
36
Refereed citations
30
Description
This paper is the second part in a series, the first part of which
presented an outline of the analysis of 60 spectra from a follow-up
program to the Two Micron Galactic Survey (TGMS) project in the l=27
deg, b=0 deg area. In this second part, we present a more detailed
explanation of the analysis, a library of the spectra for more complete
information for each of the 60 stars, and further discussions on the
implications for the structure of the Galaxy. This region contains a
prominent excess in the flux distribution and star counts previously
observed in several spectral ranges, notably in the TMGS. We found that
over 50% of the spectra of the stars detected with m_K<5.0 mag,
within a very high confidence level, correspond to stars of luminosity
class I, and a significant proportion of the remainder are very late
giants that must also be rapidly evolving. We make the case, using all
the available evidence, that we are observing a region at the nearer end
of the Galactic bar, where the Scutum spiral arm breaks away, and that
this is powerful evidence for the presence of the bar. Regions of this
type can form because of the concentrations of shocked gas where a
galactic bar meets a spiral arm, as is observed at the ends of the bars
of many face-on external galaxies. Alternative explanations do not give
nearly such a satisfactory account of the observations. Equivalent
spectroscopic analysis should also be performed at l=-22 deg, the
candidate position for the other tip of the bar. The space localization
of one and a fortiori of both ends of the bar allows us to infer its
orientation. If the second region is also confirmed to be a powerful
star formation region this would imply a position angle for the bar of
about 75 deg with respect to the Sun-Galactic center line. This geometry
is indeed compatible with the range of distances that we have obtained
for the star-forming region at l=27 deg from spectroscopic parallaxes.
However, the angle is different from that given by other authors for the
bar, and this, we think, is because they refer to the triaxial bulge and
not to the bar as detected here.