Medium resolution near-infrared spectroscopy of Massive Young Stellar
  Objects
  We present medium-resolution (R~7000) near-infrared echelle spectroscopic
data for 36 MYSOs drawn from the Red MSX Source (RMS) survey. This is the
largest sample observed at this resolution at these wavelengths of MYSOs to
date. The spectra are characterized mostly by emission from hydrogen
recombination lines and accretion diagnostic lines. One MYSO shows photospheric
HI absorption, a comparison with spectral standards indicates that the star is
an A type star with a low surface gravity, implying that the MYSOs are probably
swollen, as also suggested by evolutionary calculations. An investigation of
the Br$\gamma$ line profiles shows that most are in pure emission, while
13$\pm$5 % display P Cygni profiles, indicative of outflow, while less than
8$\pm$4 % have inverse P Cygni profiles, indicative of infall. These values are
comparable with investigations into the optically bright Herbig Be stars, but
not with those of Herbig Ae and T Tauri stars, consistent with the notion that
the more massive stars undergo accretion in a different fashion than lower mass
objects which are undergoing magnetospheric accretion. Accretion luminosities
and rates as derived from the Br$\gamma$ line luminosities agree with results
for lower mass sources, providing tentative evidence for massive star formation
theories based on scaling of low-mass scenarios. We present Br$\gamma$/Br12
line profile ratios exploiting the fact that optical depth effects can be
traced as a function of Doppler shift across the lines. These show that the
winds of MYSOs in this sample are nearly equally split between constant,
accelerating, and decelerating velocity structures. There are no trends between
the types of features we see and bolometric luminosities or near-infrared
colours.
