This paper explores the quantitative connection between globular clusters and the diffuse stellar population of the galaxies they are associated with. Both NGC 1399 and NGC 4486 (M87) are well suited for this kind of analysis due to their large globular cluster populations. The main assumption of our Monte Carlo based models is that each globular cluster is formed along with a given diffuse stellar mass that shares the same spatial distribution, chemical composition and age. The main globular cluster subpopulations, that determine the observed bimodal colour distribution, are decomposed avoiding a priori parametric (e.g. Gaussian) fits and using a new colour (C-T1)-metallicity relation. The eventual detectability of a blue tilt in the colour-magnitude diagrams of the blue globular cluster subpopulation is also addressed.
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 T1~14 to as faint as T1~22 revealing the main-sequence turnoffs of the clusters. Adopting a metallicity of Z=0.004, 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{deg} 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.
We present CCD photometry in the Washington system C and T1 passbands down to T1~18.5mag in the field of Tombaugh 1, a little studied open cluster located in the third Galactic quadrant. We measured T1 magnitudes and C-T1 colours for a total of 1351 stars distributed throughout an area of 13.6'x13.6'.
We present the first colour-magnitude relation (CMR) of early-type galaxies in the central region of the Antlia cluster, obtained from CCD wide-field photometry in the Washington photometric system. Integrated (C-T1) colours, T1 magnitudes, and effective radii have been measured for 93 galaxies (i.e. the largest galaxies sample in the Washington system till now) from the FS90 Antlia Group catalogue. Membership of 37 objects can be confirmed through new radial velocities and data collected from the literature.
As part of an ongoing project to investigate the cluster formation and chemical evolution history in the Large Magellanic Cloud (LMC), we have used the CTIO 0.9m telescope to obtain CCD imaging in the Washington system of NGC 2161, SL 874, and KMHK 1719 - three unstudied star clusters located in the outer region of the LMC. We measured T1 magnitudes and C-T1 colors for a total of 9611 stars distributed throughout cluster areas of 13.6x13.6arcmin^2^. Cluster radii were estimated from star counts distributed throughout the entire observed fields. Careful attention was paid to setting apart the cluster and field star distributions so that statistically cleaned color-magnitude diagrams (CMDs) were obtained. Based on the best fits of isochrones computed by the Padova group to the (T1, C-T1) CMDs, the {delta}T1 index, and the standard giant branch procedure, ages and metallicities were derived for the three clusters.
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 system C and T1 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.
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 CT_1_ 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 (t~6.5Gyr) . 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 ~6-7Gyr, besides the known burst at ~3Gyr.
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 0.1-1.0Gyr, as derived from the fit of isochrones with Z=0.004. 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 present CCD photometry in the Washington system C and T1 passbands down to T1~22 in the fields of L35, L45, L49, L50, L62, L63 and L85, seven poorly studied star clusters in the inner region of the Small Magellanic Cloud (SMC). We measured T1 magnitudes and C-T1 colours for a total of 114826 stars distributed throughout cluster areas of 13.7x13.7arcmin^2^ each. Cluster radii were estimated from star counts distributed throughout the entire observed fields.
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 14.7x14.7arcmin^2^ 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.
