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

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

Abstract

The VLT on Cerro Paranal was used to observe four fields located at 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 detection limit at , 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 and drops down to the 50% completeness limit at . 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 M, a value significantly higher than the M, 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 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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Contents

• 1. Introduction
• 2. Observations and data analysis
• 3. The luminosity function
• 4. Discussion and conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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