A photometric and spectroscopic study of the new dwarf spheroidal galaxy
  in Hercules
  Our aim is to provide as clean and as complete a sample as possible of red
giant branch stars that are members of the Hercules dSph galaxy. With this
sample we explore the velocity dispersion and the metallicity of the system.
Stromgren photometry and multi-fibre spectroscopy are combined to provide
information about the evolutionary state of the stars (via the Stromgren c_1
index) and their radial velocities. Based on this information we have selected
a clean sample of red giant branch stars, and show that foreground
contamination by Milky Way dwarf stars can greatly distort the results. Our
final sample consists of 28 red giant branch stars in the Hercules dSph galaxy.
Based on these stars we find a mean photometric metallicity of -2.35 dex which
is consistent with previous studies. We find evidence for an abundance spread.
Using those stars for which we have determined radial velocities we find a
systemic velocity of 45.2 km/s with a dispersion of 3.72 km/s, this is lower
than values found in the literature. Furthermore we identify the horizontal
branch and estimate the mean magnitude of the horizontal branch of the Hercules
dSph galaxy to be V_0=21.17, which corresponds to a distance of 147 kpc. We
have shown that a proper cleaning of the sample results in a smaller value for
the velocity dispersion of the system. This has implications for galaxy
properties derived from such velocity dispersions.
