The potential of Red Supergiants as extra-galactic abundance probes at
  low spectral resolution
  Red Supergiants (RSGs) are among the brightest stars in the local universe,
making them ideal candidates with which to probe the properties of their host
galaxies. However, current quantitative spectroscopic techniques require
spectral resolutions of R>17,000, making observations of RSGs at distances
greater than 1Mpc unfeasible. Here we explore the potential of quantitative
spectroscopic techniques at much lower resolutions, R ~2-3000. We take archival
J-band spectra of a sample of RSGs in the Solar neighbourhood. In this spectral
region the metallic lines of FeI, MgI, SiI and TiI are prominent, while the
molecular absorption features of OH, H_2O, CN and CO are weak. We compare these
data with synthetic spectra produced from the existing grid of model
atmospheres from the MARCS project, with the aim of deriving chemical
abundances. We find that all stars studied can be unambiguously fit by the
models, and model parameters of log g, effective temperatures Teff,
microturbulence and global metal content may be derived. We find that the
abundances derived for the stars are all very close to Solar and have low
dispersion, with an average of [logZ]=0.13+/-0.14. The values of Teff fit by
the models are ~150K cooler than the stars' literature values for earlier
spectral types when using the Levesque et al. temperature scale, though this
temperature discrepancy has very little systematic effect on the derived
abundances as the equivalent widths (EWs) of the metallic lines are roughly
constant across the full temperature range of RSGs. Instead, elemental
abundances are the dominating factor in the EWs of the diagnostic lines. Our
results suggest that chemical abundance measurements of RSGs are possible at
low- to medium-resolution, meaning that this technique is a viable
infrared-based alternative to measuring abundance trends in external galaxies.
[Abridged]
