Query : 2003A&A...399..121P

2003A&A...399..121P - Astronomy and Astrophysics, volume 399, 121-131 (2003/2-3)

HST observations of the metal rich globular clusters NGC 6496 and NGC 6352.


Abstract (from CDS):

Deep exposures of the metal-rich globular clusters NGC 6496 and NGC 6352 were obtained with the WFPC2 camera on board the Hubble Space Telescope (HST) through the F606W and F814W filters. The resulting colour-magnitude diagrams (CMD) reach down to absolute magnitude M814≃10-10.5, approximately 5 magnitudes below the main sequence (MS) turn-off (TO). The MS of the two clusters are sharp and well defined and their fiducial lines overlap almost exactly throughout this range. Their colour is, however, more than 0.1mag redder than the MS fiducial line of the prototype metal-rich globular cluster 47 Tuc (NGC 104), after proper correction for the relative distances and reddening. This provides solid empirical evidence of a higher metal content, which is not surprising if these objects belong indeed to the bulge as their present location suggests. A good fit to the upper part of the MS of both clusters is obtained with a 10Gyr-old theoretical isochrone from Baraffe et al. (1998A&A...337..403B) for a metallicity of [M/H]=-0.5, but at lower luminosities all models depart considerably from the observations, probably because of a deficiency in the treatment of the TiO opacity. The luminosity functions (LF) obtained from the observed CMD are rather similar to one another and show a peak at M814≃9. The present day mass functions (PDMF) of both clusters are derived down to M814≃10.5 or m≃0.2M and are consistent with power-law indices α=0.7 for NGC 6496 and α=0.6 for NGC 6352. The PDMF of NGC 104 is twice as steep in the same mass range (α=1.4). We investigate the origin of this discrepancy and show that it can be understood if the two clusters contain a considerably higher fraction of primordial binaries amongst their MS population, similar to that expected in the bulge. We briefly discuss the implications of this finding on the process of star and binary formation and on the universality of the IMF.

Abstract Copyright:

Journal keyword(s): stars: Hertzsprung-Russell (HR) and C-M diagrams - stars: luminosity function, mass function - Galaxy: globular clusters: individual: NGC 6496, NGC 6352

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 NGC 104 GlC 00 24 05.359 -72 04 53.20     4.09     ~ 3889 0
2 NGC 6352 GlC 17 25 29.11 -48 25 19.8           ~ 395 0
3 NGC 6496 GlC 17 59 03.68 -44 15 57.4   9.96       ~ 224 0
4 NGC 6624 GlC 18 23 40.51 -30 21 39.7           ~ 880 1
5 M 69 GlC 18 31 23.10 -32 20 53.1           ~ 461 0

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