  A rich harvest of RR Lyrae stars has been identified for the first time in
B514, a metal-poor ([Fe/H] = 1.95 +/- 0.10 dex) globular cluster of the
Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary
Camera 2 and Advanced Camera for Surveys time-series observations. We have
detected and derived periods for 89 RR Lyrae stars (82 fundamental-mode -RRab-
and 7 first-overtone -RRc- pulsators, respectively) among 161 candidate
variables identified in the cluster. The average period of the RR Lyrae
variables (<Pab> = 0.58 days and <Pc> = 0.35 days, for RRab and RRc pulsators,
respectively) and the position in the period-amplitude diagram both suggest
that B514 is likely an Oosterhoff type I cluster. This appears to be in
disagreement with the general behaviour of the metal-poor globular clusters in
the Milky Way, which show instead Oosterhoff type II pulsation properties. The
average apparent magnitude of the RR Lyrae stars sets the mean level of the
cluster horizontal branch at <V(RR)> = 25.18 +/- 0.02 (sigma=0.16 mag, on 81
stars). By adopting a reddening E(B-V) = 0.07 +/- 0.02 mag, the above
metallicity and M_V=0.44 +/- 0.05 mag for the RR Lyrae variables of this
metallicity, we derive a distance modulus of mu_0=24.52 +/- 0.08 mag,
corresponding to a distance of about 800 +/- 30 kpc, based on a value of M_V
that sets mu_0(LMC)=18.52.
