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Astron. Astrophys. 343, L9-L14 (1999)

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Letter to the Editor

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

Guido De Marchi, Bruno Leibundgut, Francesco Paresce and Luigi Pulone

European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany (demarchi@eso.org, bleibund@eso.org, fparesce@eso.org, lpulone@eso.org)

Received 21 October 1998 / Accepted 3 November 1998


The VLT on Cerro Paranal was used to observe four fields located at [FORMULA] 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 main sequence reaching down to the [FORMULA] detection limit at [FORMULA], [FORMULA] or approximately 4 magnitudes below the main sequence turn-off, the deepest obtained so far on this cluster. This yields a main sequence luminosity function that peaks at [FORMULA] and drops down to the 50% completeness limit at [FORMULA]. Transformation to a mass function via the latest mass-luminosity relation appropriate to this object indicates that the peak of the luminosity function corresponds to [FORMULA] M[FORMULA], a value significantly higher than the [FORMULA] M[FORMULA], measured for most other clusters observed so far. Since this object, in its Galactic orbit, penetrates very deeply into the Galactic bulge with perigalactic distance of [FORMULA] kpc, this result is the first strong evidence that tidal forces have stripped this cluster of a substantial portion of its lower mass star population all the way down to its half-light radius and possibly beyond.

Key words: stars: luminosity function, mass function – stars: low-mass, brown dwarfs – stars: Population II – Galaxy: globular clusters: general – Galaxy: globular clusters: individual: NGC 6712

* Based on observations collected at the European Southern Observatory, Paranal, Chile (VLT-UT1 Science Verification Program)

Send offprint requests to: Guido De Marchi

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© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999