Identifying two groups of massive stars aligned in the $l\sim38^{\circ}$
  Galactic direction
  Context: Recent near-infrared data have contributed to unveil massive and
obscured stellar populations in both new and previously known clusters in our
Galaxy. These discoveries lead us to view the Milky Way as an active
star-forming machine. Aims: We look for young massive cluster candidates as
over-densities of OB-type stars. The first search, focused on the Galactic
direction $l=38^{\circ}$, resulted in the detection of two objects with a
remarkable population of OB-type star candidates. Methods: With a modified
version of the friends-of-friends algorithm AUTOPOP and using 2MASS and
UKIDSS-GPS near-infrared ($J$, $H$, and $K$) photometry for one of our cluster
candidates (named Masgomas-6) we selected 30 stars for multi-object and
long-slit $H$- and $K$-spectroscopy. With the spectral classification and the
near-infrared photometric data, we derive individual distance, extinction and
radial velocity. Results: Of the 30 spectroscopically observed stars, 20 are
classified as massive stars, including OB-types (dwarfs, giants and
supergiants), two red supergiants, two Wolf-Rayet (WR122-11 and the new
WR122-16), and one transitional object (the LBV candidate IRAS 18576+0341). The
individual distances and radial velocities do not agree with a single cluster,
indicating that we are observing two populations of massive stars in the same
line-of-sight: Masgomas-6a and Masgomas-6b. The first group of massive stars,
located at 3.9$^{+0.4}_{-0.3}$ kpc, contains both Wolf-Rayets and most of the
OB-dwarfs, and Masgomas-6b, at $9.6\pm0.4$ kpc, hosts the LBV candidate and an
evolved population of supergiants. We are able to identify massive stars at two
Galactic arms, but we can not clearly identify whether these massive stars form
clusters or associations.
