1999AJ....118..381L

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°, b=0° 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°, 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° 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° 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.