J. F. C. Santos

A general catalogue of extended objects in the Magellanic System

We update the Small Magellanic Cloud (SMC), Bridge and Large Magellanic Cloud (LMC) catalogues of extended objects that were constructed by members of our group from 1995 to 2000. In addition to the rich subsequent literature for the previous classes, we now also include H I shells and supershells. A total of 9305 objects were cross-identified, while our previous catalogues amounted to 7900 entries, an increase of ≈12 per cent. We present the results in subcatalogues containing 1445 emission nebulae, 3740 star clusters, 3326 associations and 794 H I shells and supershells. Angular and apparent size distributions of the extended objects are analysed. We conclude that the objects, in general, appear to respond to tidal effects arising from the LMC, SMC and Bridge. Number-density profiles extracted along directions parallel and perpendicular to the LMC bar, can be described by two exponential-discs. A single exponential-disc fits the equivalent SMC profiles. Interestingly, when angular-averaged number-densities of most of the extended objects are considered, the profiles of both Clouds do not follow an exponential-disc. Rather, they are best described by a tidally truncated, core/halo profile, despite the fact that the Clouds are clearly disturbed discs. On the other hand, the older star clusters taken isolately, distribute as an exponential disc. The present catalogue is an important tool for the unambiguous identification of previous objects in current CCD surveys and to establish new findings.

The Line-of-Sight Depth of Populous Clusters in the Small Magellanic Cloud

We present an analysis of age, metal abundance, and positional data on populous clusters in the Small Magellanic Cloud (SMC) with the ultimate aim of determining the line-of-sight (LOS) depth of the SMC by using these clusters as proxies. Our data set contains 12 objects and is limited to clusters with the highest-quality data for which the ages and abundances are best known and can be placed on an inter- nally consistent scale. We have analyzed the variation of the clustersproperties with position on the sky and with line-of-sight depth. Based on this analysis, we draw the following conclusions: (1) The obser- vational data indicate that the eastern side of the SMC (facing the Large Magellanic Cloud) contains younger and more metal-rich clusters as compared with the western side. This is not a strong correlation because our data set of clusters is necessarily limited, but it is suggestive and warrants further study. (2) Depending on how the reddening is computed to our clusters, we —nd a mean distance modulus that ranges from to 18.82 ^ 0.05. (3) The intrinsic ^1 p LOS depth of the SMC (m ( M) 0 \ 18.71 ^ 0.06 populous clusters in our study is between D6 and D12 kpc, depending primarily on whether we adopt the Burstein & Heiles reddenings or those from Schlegel et al. (4) Viewing the SMC as a triaxial galaxy with declination, right ascension, and LOS depth as the three axes, we —nd axial ratios of approximately 1:2:4. Taken together, these conclusions largely agree with those of previous investigators and under- score the utility of populous star clusters as probes of the structure of the Small Magellanic Cloud.

Ages and Metallicities of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud

We present Washington system CT1 color-magnitude diagrams of 13 star clusters and their surrounding fields that lie in the outer parts of the LMC disk (r > 4°), as well as a comparison inner cluster. The total area covered is large ( deg2), 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 δT1 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° (the deprojected distance of ESO 121-SC03), or ~11 kpc, but not to 13° (~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).

Mass functions and structure of the young open cluster NGC 6611

We use J , H  and K S  2MASS photometry to study colour–magnitude (CMDs) and colour–colour diagrams, structure and mass distribution in the ionizing open cluster NGC 6611. Reddening variation throughout the cluster region is taken into account followed by field-star decontamination of the CMDs. Decontamination is also applied to derive the density profile and luminosity functions in the core, halo and overall (whole cluster) regions. The field-star decontamination showed that the lower limit of the main sequence (MS) occurs at ≈

Spatial dependence of 2MASS luminosity and mass functions in the old open cluster NGC 188

5\,\mbox{

An optical/NIR survey of globular clusters in early-type galaxies. II. Ages of globular cluster systems and the relation to galaxy morphology

M_\odot

Ages and metallicities of star clusters: New calibrations and diagnostic diagrams from visible integrated spectra

}

Characterization and photometric membership of the open cluster NGC 1981

. Based on the fraction of K S  excess stars in the colour–colour diagram we estimate an age of

Spectral evolution of star clusters in the Large Magellanic Cloud. I. Blue concentrated clusters in the age range 40-300 Myr

1.3\pm0.3

Mass distribution and structural parameters of Small Magellanic Cloud star clusters

 Myr which is consistent with the presence of a large number of pre-main sequence (PMS) stars. The distance from the Sun was estimated from known O V stars in the cluster area and the turn-on stars connecting the PMS and MS, resulting in