Origins of Massive Field Stars in the Galactic Center: a Spectroscopic
  Study
  Outside of the known star clusters in the Galactic Center, a large number of
evolved massive stars have been detected; but their origins remain uncertain.
We present a spectroscopic study of eight such stars, based on new Gemini GNIRS
and NIFS near-infrared observations. This work has led to the discovery of a
new O If+ star. We compare the reddening-corrected J-K vs K diagram for our
stars with the massive ones in the Arches cluster and use stellar evolutionary
tracks to constrain their ages and masses. The radial velocities of both the
stars and their nearby H II regions are also reported. All of the stars are
blueshifted relative to the Arches cluster by > 50 km/s. We find that our
source P35 has a velocity consistent with that of the surrounding molecular
gas. The velocity gradient of nearby ionized gas along the Gemini GNIRS long
slit, relative to P35 and the adjacent -30-0 km/s molecular cloud, can best be
explained by a pressure-driven flow model. Thus, P35 most likely formed in
situ. Three more of our stars have radial velocities different from their
adjacent molecular gas, indicating that they are interlopers. The four stars
closest to the Arches cluster have similar spectra, ages and masses to known
cluster members, suggesting that they were likely ejected from the cluster via
three-body interactions. Therefore, we find that the relatively isolated stars
partly formed in situ and partly were ejected from the known star clusters in
the Galactic Center.
