Bibcode
Perina, S.; Barmby, P.; Beasley, M. A.; Bellazzini, M.; Brodie, J. P.; Burstein, D.; Cohen, J. G.; Federici, L.; Fusi Pecci, F.; Galleti, S.; Hodge, P. W.; Huchra, J. P.; Kissler-Patig, M.; Puzia, T. H.; Strader, J.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 494, Issue 3, 2009, pp.933-948
Fecha de publicación:
2
2009
Revista
Número de citas
29
Número de citas referidas
29
Descripción
Aims: We introduce our imaging survey of possible young massive globular
clusters in M31 performed with the Wide Field and Planetary Camera 2
(WFPC2) on the Hubble Space Telescope (HST). We obtained shallow (to
B˜ 25) photometry of individual stars in 20 candidate clusters. We
present here details of the data reduction pipeline that is being
applied to all the survey data and describe its application to the
brightest among our targets, van den Bergh 0 (VdB0), taken as a test
case. Methods: Point spread function fitting photometry of
individual stars was obtained for all the WFPC2 images of VdB0 and the
completeness of the final samples was estimated using an extensive set
of artificial stars experiments. The reddening, the age and the
metallicity of the cluster were estimated by comparing the observed
color magnitude diagram (CMD) with theoretical isochrones. Structural
parameters were obtained from model-fitting to the intensity profiles
measured within circular apertures on the WFPC2 images. Results:
Under the most conservative assumptions, the stellar mass of VdB0 is
M> 2.4 × 10^4 M&sun;, but our best estimates lie in
the range ≃4{-}9 × 10^4 M&sun;. The CMD of VdB0 is
best reproduced by models having solar metallicity and age ≃ 25
Myr. Ages less than ≃12 Myr and greater than ≃60 Myr are
clearly ruled out by the available data. The cluster has a remarkable
number of red super giants (⪆18) and a CMD very similar to Large
Magellanic Cloud clusters usually classified as young globulars such as
NGC 1850, for example. Conclusions: VdB0 is significantly brighter
(⪆1 mag) than Galactic open clusters of similar age. Its present-day
mass and half-light radius (r_h=7.4 pc) are more typical of faint
globular clusters than of open clusters. However, given its position
within the disk of M31, it is expected to be destroyed by dynamical
effects, in particular by encounters with giant molecular clouds, within
the next 4 Gyr.
Based on observations made with the NASA/ESA
Hubble Space Telescope, obtained at the Space Telescope Science
Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555.
These observations are associated with program GO-10818 [P.I.: J. G.
Cohen].