INVESTIGADORES
PIATTI Andres Eduardo
artículos
Título:
Ages and metallicities of star clusters and surrounding fields in the outer disk of the large magellanic cloud
Autor/es:
BICA, EDUARDO; GEISLER, DOUG; DOTTORI, HORACIO; CLARIA OLMEDO, JUAN JOSÉ; PIATTI, ANDRÉS E.; SANTOS JR, JOÂO FC
Revista:
ASTRONOMICAL JOURNAL
Referencias:
Año: 1998 vol. 116 p. 723 - 737
ISSN:
0004-6256
Resumen:
We present Washington system CT_1 color-magnitude diagrams of 13 star
clusters and their surrounding fields that lie in the outer parts of the
LMC disk (r > 4 deg), as well as a comparison inner cluster. The
total area covered is large (2/3 deg^2), allowing us to study the
clusters and their fields individually and in the context of the entire
Galaxy. Ages are determined by means of the magnitude difference
deltaT_1 between the giant branch clump and the turnoff, while
metallicities are derived from the location of the giant and subgiant
branches as compared with fiducial star clusters. This yields a unique
data set in which ages and metallicities for both a significant sample
of clusters and their fields are determined homogeneously. We find that
in most cases the stellar population of each star cluster is quite
similar to that of the field where it is embedded, sharing its mean age
and metallicity. The old population (t >= 10 Gyr) is detected in most
fields as a small concentration of stars on the horizontal branch
blueward and faintward of the prominent clump. Three particular fields
present remarkable properties: (1) The thus-far unique cluster ESO
121-SC03 at ~9 Gyr has a surrounding field that shares the same
properties (which, in turn, is also unique, in that such a dominant
old-field component is not present elsewhere-at least not significantly
in the fields as yet studied). (2) The field surrounding the far eastern
intermediate-age cluster OHSC 37 is noteworthy in that we do not detect
any evidence of LMC stars: it is essentially a Galactic foreground
field. We can thus detect the LMC field out to greater than 11 deg (the
deprojected distance of ESO 121-SC03), or ~11 kpc, but not to 13 deg
(~13 kpc), despite the presence of clusters at this distance. (3) In the
northern part of the LMC disk, the fields of SL 388 and SL 509 present
color-magnitude diagrams with a secondary clump ~0.45 mag fainter than
the dominant intermediate-age clump, suggesting a stellar population
component located behind the LMC disk at a distance comparable to that
of the SMC. Possibly we are witnessing a depth effect in the LMC, and
the size of the corresponding structure is comparable to the size of a
dwarf galaxy. The unusual spatial location of the cluster OHSC 37 and
the anomalous properties of the SL 388 and SL 509 fields might be
explained as debris from previous LMC interactions with the Galaxy
and/or the SMC. The mean metallicity derived for the intermediate-age
outer disk clusters is <[Fe/H]> = -0.66, and for their surrounding
fields <[Fe/H]> = -0.56. These values are significantly lower than
those found by Olszewski et al. for a sample of clusters of similar age
but are in good agreement with several recent studies. A few clusters
stand out in the age-metallicity relation, in that they are
intermediate-age clusters at relatively low metallicity ([Fe/H] ~ -1).