Issue |
A&A
Volume 372, Number 3, June IV 2001
|
|
---|---|---|
Page(s) | 851 - 861 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20010402 | |
Published online | 15 June 2001 |
VLT observations of the peculiar globular cluster NGC 6712*
II. luminosity and mass functions
1
Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Rome, Italy
2
European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
3
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4
Affiliated with the Astrophysics Division, Space Science Department, European Space Agency
5
Osservatorio Astronomico di Bologna, Via Ranzani 1, 40127, Bologna, Italy
Corresponding author: G. De Marchi, demarchi@stsci.edu
Received:
20
September
2000
Accepted:
13
March
2001
We have carried out extensive VLT-FORS1 observations covering a fair
fraction of the intermediate metallicity globular cluster NGC 6712 in
the V and R bands. We derive accurate colour-magnitude diagrammes
(CMD) and luminosity functions (LFs) of the cluster main sequence (MS)
for four overlapping fields extending from the centre of the cluster
out to a radius of ~, well beyond the nominal tidal
radius, and for a control field at ~
distance. The LFs
extend from the cluster turn-off (TO) at
to the point at
which the incompleteness drops below 50% (corresponding to
or
) for most fields studied. Cluster stars
become indistinguishable from field stars at
. The
shape of the cluster's LF and its variation with distance from the
centre in these ranges are well described by a standard multi-mass
static model having the following parameters: core radius
, half-light radius
, tidal radius
, concentration ratio
, and a power-law
global mass function (MF) with index
for masses
smaller than 0.8
, i.e. for all detected MS stars, and
for evolved objects. The MF obtained in this way is
consistent with that found in a preliminary investigation of this
cluster with the VLT Test Camera and confirms that this is the only
globular cluster known so far for which the global MF drops with
decreasing mass below the TO. Possible reasons for this unique
characteristic are discussed with the most likely associated with its
extreme vulnerability to tidal disruption.
Key words: globular clusters: general / globular clusters: individual: NGC 6712 / stars: luminosity function, mass function / stars: low-mass, brown dwarfs / stars: Population II
© ESO, 2001
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