A deep optical luminosity function of NGC 6712 with the VLT: Evidence for severe tidal disruption

The VLT on Cerro Paranal was used to observe four fields located at similar to 2'.3 from the center of the Galactic globular cluster NGC 6712 in the V and R bands. The resulting color magnitude diagram shows a well defined ma in sequence reaching down to the 5 sigma detection limit at V similar or eq ual to 25, R similar or equal to 23.5 or approximately 4 magnitudes below t he main sequence turn-off, the deepest obtained so far on this cluster. Thi s yields a main sequence luminosity function that peaks at M-R similar or e qual to 4.5 and drops down to the 50% completeness limit at M-R similar or equal to 8.5. Transformation to a mass function via the latest mass-luminos ity relation appropriate to this object indicates that the peak of the lumi nosity function corresponds to similar to 0.75M(.), a value significantly h igher than the similar to 0.25 M-., measured for most other clusters observ ed so far. Since this object, in its Galactic orbit, penetrates very deeply into the Galactic bulge with perigalactic distance of similar to 0.3 kpc, this result is the first strong evidence that tidal forces have stripped th is cluster of a substantial portion of its lower mass star population all t he way down to its half-light radius and possibly beyond.