Spectroscopic Observations of Obscured Populations in the Inner Galaxy:
  2MASS-GC02, Terzan 4, and the 200 km/s stellar peak
  The interpretation of potentially new and already known stellar structures
located at low-latitudes is hindered by the presence of dense gas and dust, as
observations toward these sight-lines are limited. We have identified APOGEE
stars belonging to the low-latitude globular clusters 2MASS-GC02 and Terzan 4,
presenting the first chemical element abundances of stars residing in these
poorly studied clusters. As expected, the signature of multiple populations
co-existing in these metal-rich clusters is evident. We redetermine the radial
velocity of 2MASS-GC02 to be -87 +- 7 km/s, finding that this cluster's
heliocentric radial velocity is offset by more than 150 km/s from the
literature value. We investigate a potentially new low-latitude stellar
structure, a kiloparsec-scale nuclear disk (or ring) which has been put forward
to explain a high-velocity (V_{GSR} ~200 km/s) peak reported in several
Galactic bulge fields based on the APOGEE commissioning observations. New
radial velocities of field stars at (l,b)=(-6,0) are presented and combined
with the APOGEE observations at negative longitudes to carry out this search.
Unfortunately no prominent -200 km/s peak at negative longitudes along the
plane of the Milky Way is apparent, as predicted for the signature of a nuclear
feature. The distances and Gaia EDR3 proper motions of the high-V_{GSR} stars
do not support the current models of stars on bar-supporting orbits as an
explanation of the +200 km/s peak.
