Bibcode
DOI
Bertelli, Gianpaolo; Nasi, Emma; Girardi, Leo; Chiosi, Cesare; Zoccali, Manuela; Gallart, Carme
Bibliographical reference
The Astronomical Journal, Volume 125, Issue 2, pp. 770-784.
Advertised on:
2
2003
Citations
81
Refereed citations
72
Description
The color-magnitude diagrams (CMDs) of three intermediate-age Large
Megallanic Cloud clusters, NGC 2173, SL 556, and NGC 2155, are analyzed
to determine their age and metallicity based on Padova stellar models.
Synthetic CMDs are compared with cluster data. The best match is
obtained using two fitting functions based on star counts in the
different bins of the cluster CMD. Two different criteria are used. One
of them takes into account the uncertainties in the color of the red
clump stars. Given the uncertainties on the experimental values of the
clusters metallicity, we provide a set of acceptable solutions. They
define the corresponding values of metallicity, age, reddening and
distance modulus (for the assumed initial mass function). The comparison
with Padova models suggests for NGC 2173 a prolonged star formation
(spanning a period of about 0.3 Gyr), beginning 1.7 Gyr and ending 1.4
Gyr ago. The metallicity Z is in the range 0.0016-0.003. For SL 556 an
age of 2.0 Gyr is obtained. The metallicity value is in the range
0.002-0.004, depending on the adopted comparison criterion. The derived
age for NGC 2155 is 2.8 Gyr, and its metallicity Z is in the range
0.002-0.003. The CMD features of this cluster suggest that a more
efficient overshoot should be adopted in the evolutionary models. A
period of extended star formation is not required to fit the SL 556 and
NGC 2155 observations.
Based on observations collected at the European Southern Observatory,
Paranal, Chile.