Photometric distances to young stars in the inner galactic disk
  We present results of the first extensive and deep CCD photometric survey
carried out in the field of the open cluster Trumpler 27, an object in the
constellation of Sagittarius not far from the Galaxy center.
  We look for young stars clumps that might plausibly be associated with spiral
structure. Wide-field UBVI photometry combined with infrared information allows
us to reconstruct the distribution in reddening and distance of young stars in
the field using the Color-Color and Color-Magnitude diagrams.
  The analysis of our data, combined too with extensive spectroscopy taken from
literature shows that the real entity of Trumpler 27 as an open cluster is far
from being firmly stated. In fact, instead of finding a relatively compact
group of stars confined to a small distance range, we found that stars
associated to Trumpler 27 are, indeed, a superposition of early type stars seen
along the line of sight extending over several kiloparsecs beyond even the
center of the galaxy. We demonstrate that at each distance range it becomes
possible to generate a color-magnitude diagram resembling that of an open
cluster. This way, our analysis indicates that what was considered an open
cluster characterized by a significant age spread is a stellar continuum that
reaches its maximum number of stars at approximately 3.5 kpc from the Sun, the
distance of the Scutum-Crux arm approximately. At the same time, and after
analyzing the way early type stars distribute with distance, we found some of
these stellar groups may be linked, within the distance errors, with other
inner spiral arms of our galaxy, including the Near 3 kpc arm at approximately
5 kpc from the Sun. However, very young stars by themselves do not seem to
trace strongly the inner spiral arms since they are distributed evenly across
several kiloparsecs toward the center of the Galaxy.
