2009ApJ...706L.150A

We present a new mass estimate for the Hercules dwarf spheroidal (dSph) galaxy, based on the revised velocity dispersion obtained by Adén et al. The removal of a significant foreground contamination using newly acquired Strömgren photometry has resulted in a reduced velocity dispersion. Using this new velocity dispersion of 3.72±0.91 km/s, we find a mass of M ₃₀₀= 1.9^+1.1_–0.8x10⁶ M_☉within the central 300 pc, which is also the half-light radius, and a mass of M₄₃₃= 3.7^+2.2_–1.6x 10⁶ M_☉ within the reach of our data to 433 pc, significantly lower than previous estimates. We derive an overall mass-to-light ratio of M₄₃₃/L = 103⁺⁸³_–48[M_☉/L_☉]. Our mass estimate calls into question recent claims of a common mass scale for dSph galaxies. Additionally, we find tentative evidence for a velocity gradient in our kinematic data of 16±3 km/s/kpc, and evidence of an asymmetric extension in the light distribution at ∼0.5 kpc. We explore the possibility that these features are due to tidal interactions with the Milky Way. We show that there is a self-consistent model in which Hercules has an assumed tidal radius of r_t = 485 pc, an orbital pericenter of r_p= 18.5±5 kpc, and a mass within r_t of. Proper motions are required to test this model. Although we cannot exclude models in which Hercules contains no dark matter, we argue that Hercules is more likely to be a dark-matter-dominated system that is currently experiencing some tidal disturbance of its outer parts.