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We leverage new high-quality data from Hubble Space Telescope program GO-14164 to explore the variation in horizontal branch morphology among globular clusters in the Large Magellanic Cloud (LMC). Our new observations lead to photometry with a precision commensurate with that available for the Galactic globular cluster population. Our analysis indicates that, once metallicity is accounted for, clusters in the LMC largely share similar horizontal branch morphologies regardless of their location within the system. Furthermore, the LMC clusters possess, on average, slightly redder morphologies than most of the inner halo Galactic population; we find, instead, that their characteristics tend to be more similar to those exhibited by clusters in the outer Galactic halo. Our results are consistent with previous studies, showing a correlation between horizontal branch morphology and age. [ABSTRACT FROM AUTHOR]

ABSTRACT We present CCD photometry in the Washington system C, T1 and T2 passbands down to T1∼ 23 in the fields of L3, L28, HW 66, L100, HW 79, IC 1708, L106, L108, L109, NGC 643, L112, HW 84, HW 85 and HW 86, 14 Small Magellanic Cloud (SMC) clusters, most of them poorly studied objects. We measured T1 magnitudes and C− T1 and T1− T2 colours for a total of 213 516 stars spread throughout cluster areas of 14.7 × 14.7 arcmin2 each. We carried out an in-depth analysis of the field star contamination of the colour-magnitude diagrams (CMDs) and statistically cleaned the cluster CMDs. Based on the best fits of isochrones computed by the Padova group to the ( T1, C− T1) CMDs, as well as from the δ( T1) index and the standard giant branch procedure, we derived ages and metallicities for the cluster sample. With the exception of IC 1708, a relatively metal-poor Hyades-age cluster, the remaining 13 objects are between intermediate and old age (from 1.0 to 6.3 Gyr), their [Fe/H] values ranging from −1.4 to −0.7 dex. By combining these results with others available in the literature, we compiled a sample of 43 well-known SMC clusters older than 1 Gyr, with which we produced a revised age distribution. We found that the present clusters' age distribution reveals two primary excesses of clusters at t∼ 2 and 5 Gyr, which engraves the SMC with clear signs of enhanced formation episodes at both ages. In addition, we found that from the birth of the SMC cluster system until approximately the first 4 Gyr of its lifetime, the cluster formation resembles that of a constant formation rate scenario. [ABSTRACT FROM AUTHOR]

Colour–magnitude diagrams in the Washington system are presented for the first time for five star clusters projected on to the outer region of the Small Magellanic Cloud (SMC). The clusters are found to have ages in the range 0.1–1.0 Gyr, as derived from the fit of isochrones with . This sample increases substantially the number of young clusters in the outer SMC – particularly in the south-east quadrant – with well-derived parameters. We combine our results with those for other clusters in the literature to derive as large and homogeneous a data base as possible (totalling 49 clusters) in order to study global effects. We find no conclusive evidence for a dispersion in the cluster ages and metallicities as a function of their distance from the galaxy centre, in the SMC outer region. L 114 and 115, although very distant, are very young clusters, lying in the bridge of the SMC and therefore most likely formed during the interaction which formed this feature. We also find very good agreement between the cluster age–metallicity relation (AMR) and the prediction from a bursting model from Pagel & Tautvaišienė with a burst that occurred 3 Gyr ago. Comparing the present cluster AMR with that derived by Harris & Zaritsky for field stars in the main body of the SMC, we find that field stars and clusters underwent similar chemical enrichment histories during approximately the last couple of Gyr, but their chemical evolution was clearly different between 4 and 10 Gyr ago. [ABSTRACT FROM AUTHOR]

We present CCD photometry in the Washington C and T1 filters for six star clusters (B 34, NGC 256, NGC 265, NGC 294, IC 1611 and NGC 376) in the Small Magellanic Cloud (SMC) and their surrounding fields. The resultant colour–magnitude diagrams (CMDs) extend from to as faint as revealing the main-sequence turnoffs of the clusters. Adopting a metallicity of , we compare our cluster photometry with theoretical isochrones in the Washington system in order to derive ages. To facilitate age determination of the surrounding fields, we use the magnitude difference between the helium-burning red clump stars and the main-sequence turnoff. Finally, we estimate mean metallicities for the field stars by comparing the location of the field red giant branch with standard giant branches for Galactic globular clusters of known abundance, corrected for age effects. Combining these results with our previous work, we find a clear trend of younger clusters being located closer to the centre of the SMC. In addition, there is a tendency for the mean metallicity and its dispersion to be greater inside 4° of the SMC's centre as compared to outside this radius. As far as the properties of the field stars are concerned, we find little correlation between the ages of the clusters and those of the field stars against which they are projected. Clearly, more work needs to be done to clarify these trends. [ABSTRACT FROM AUTHOR]

Colour–magnitude diagrams (CMDs) are presented for the first time for 10 star clusters projected on to the Small Magellanic Cloud (SMC). The photometry was carried out in the Washington systemCandT1 filters allowing the determination of ages by means of the magnitude difference between the red giant clump and the main-sequence turnoff (MSTO), and metallicities from the red giant branch (RGB) locus. The clusters all have ages in the range 1.5–4 Gyr and metallicities between, with respective errors of∼0.5 Gyr and 0.3 dex. This increases substantially the sample of intermediate-age clusters in the SMC with well-derived parameters. We combine our results with those for other clusters in the literature to derive as large and homogeneous a data base as possible (totalling 26 clusters) in order to study global effects. We find evidence for two peaks in the age distribution of SMC clusters, at∼6.5 and 2.5 Gyr, in good agreement with previous hints involving smaller samples. The most recent peak occurs at a time that corresponds to a very close encounter between the Large Magellanic Cloud (LMC) and the SMC according to the recent dynamical models of Bekki et al. that they used to explain the enhancement of LMC clusters with this age. It appears cluster formation may have been similarly stimulated in the SMC by this encounter as well. We also find very good agreement between cluster ages and metallicities and the prediction from a bursting model from Pagel and Tautvaišienė with a burst that occurred 3 Gyr ago. These two lines of evidence together favour a bursting cluster formation history as opposed to a continuous one for the SMC. [ABSTRACT FROM AUTHOR]

Reports on photometric studies on intermediate age and young Large Magellanic Cloud (LMC) star clusters. Derivation of ages and metallicities with theoretical isochrones; Use of homogeneous parameter determinations to probe the chemical enrichment of the LMC; Evidence of solar metal content in the inner disc clusters.

ABSTRACT We present Washington System photometry for 11 star clusters immersed in the north-west part of the Large Magellanic Cloud (LMC) bar, centred on the intermediate-age clusters NGC 1865 and SL 244. The fields are heavily populated by the intermediate-age component of the LMC bar. We succeeded in disentangling cluster colour–magnitude diagrams from those of the fields and in deriving reddening and ages for five clusters – SL 218, BRHT4b, and NGC 1839, 1838 and 1863 – with the aid of recent Washington System theoretical isochrones. The resulting cluster ages range between 50 and 125 Myr. Despite their proximity, NGC 1836 and BRHT4b have very different ages. Thus the possibility of these two objects being a binary cluster is very unlikely, although a capture cannot be ruled out a priori. Our results suggest that for each intermediate-age cluster remaining in the LMC bar region, a number of robust young blue star clusters occurs in the same region. [ABSTRACT FROM AUTHOR]

ABSTRACT We present Washington system colour–magnitude diagrams for 8 star clusters and their surrounding fields which, with one exception, lie within the inner parts of the Large Magellanic Cloud (LMC) disc. Careful attention is paid to separating out the cluster and field star distributions. Ages and metallicities are then determined in a consistent manner for both populations in two different ways. We first compare the colour–magnitude diagrams (CMDs) with new theoretical isochrones in the Washington system. We also derive ages using the magnitude difference between the red clump and the turnoff, and derive metallicities by comparing the giant branches to standard calibrating clusters. For this latter metallicity derivation, we present age-dependent metallicity corrections for intermediate age clusters (IACs) based on the new isochrones. The two methods for both age and metallicity determination are in good agreement with each other. All clusters are found to be IACs (1–3 Gyr), with [Fe/H] from -0.4 to -0.9. We find that the stellar population of each star cluster is generally quite similar to that of the field where it is embedded, sharing its mean age and metallicity. Combining the present sample with a revision of that of Bica et al. studied similarly, we find that our metallicities for IACs are intermediate in metallicity to those for clusters of similar age studied by Olszewski et al. and by Beasley, Hoyle & Sharples. A combined age–metallicity relation is presented which shows that LMC clusters formed between 1–3 Gyr ago with a mean metallicity (–0.5 dex) and metallicity spread (0.23 dex) independent of age. Good agreement is found with the bursting model of Pagel & Tautvaivˇienė. No evidence for a metallicity gradient is found. [ABSTRACT FROM AUTHOR]

We present the results on the age and metallicity estimates of the Small Magellanic Cloud (SMC) clusters L 110, L 112 and L 113 obtained from CCD Washington CT1 photometry. We confirm L 113 as a relatively old and metal-poor cluster, and report for the first time that L 110 and 112 are also relatively old clusters . Their derived ages and metallicities reinforce previous suggestions that the farther a cluster is from the centre of the galaxy, the older and more metal-poor it is, with some dispersion. In addition, the bursting star formation model still appears to be the most probable paradigm to describe the SMC's star formation history. We call attention to a second possible burst at ∼6–7 Gyr, besides the known burst at ∼3 Gyr. [ABSTRACT FROM AUTHOR]