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Context.NGC 1380 is a lenticular galaxy located near the centre of the Fornax Cluster, northeast of NGC 1399. The globular cluster system of this galaxy has hitherto only been studied from the ground. Recent studies of similar early-type galaxies, specially lenticular ones, reveal the existence of star clusters that apparently break up the traditional open/globular cluster dichotomy.

Aims.We analyzed HST/WFPC2 colour–magnitude diagrams (CMDs) of 15 populous Large Magellanic Cloud (LMC) stellar clusters with ages between ~0.3 Gyr and ~3 Gyr. These (V, $B-V$) CMDs are photometrically homogeneous and typically reach $V \sim 22$. Accurate and self-consistent physical parameters (age, metallicity, distance modulus and reddening) were extracted for each cluster by comparing the observed CMDs with synthetic ones.

Context.We have obtained BVRIphotometry for 21 stellar fields located in directions towards the central $3.5^\circ$of the Galaxy. Each field is $10\times 10$arcmin in size, and a total of ~$2 \times 10^5$stars were measured.

Context.NGC 5846 is a giant elliptical galaxy with a previously well studied globular cluster system (GCS), known to have a bimodal colour distribution with a remarkably high red fraction.

Aims.We used the deep colour–magnitude diagrams (CMDs) of five rich LMC clusters (NGC 1805, NGC 1818, NGC 1831, NGC 1868, and Hodge 14) observed with HST/WFPC2 to derive their present day mass function (PDMF) and its variation with position within the cluster.

We use the open clusters (OCs) with known parameters available in the WEBDA database and in recently published papers to derive properties related to the disk structure such as the thin-disk scale height, displacement of the Sun above the Galactic plane, scale length and the OC age-distribution function. The sample totals 654 OCs, consisting basically of Trumpler types I to III clusters whose spatial distribution traces out the local geometry of the Galaxy. We find that the population of OCs with ages younger than 200 Myr distributes in the disk following an exponential-decay profile with a scale height of zhpc. For the clusters with ages in the range 200 Myr to 1 Gyr we derive zhpc. Clusters older than 1 Gyr distribute nearly uniformly in height from the plane so that no scale height can be derived from exponential fits. Considering clusters of all ages we obtain an average scale height of zhpc. We confirm previous results that zhincreases with Galactocentric distance. The scale height implied by the OCs younger than 1 Gyr outside the Solar circle is a factor ${\sim}1.4{-}2$larger than zhof those interior to the Solar circle. We derive the displacement of the Sun above the Galactic plane as $\rm\mbox{$z_\odot$}=14.8\pm2.4$pc, which agrees with previous determinations using stars. As a consequence of the completeness effects, the observed radial distribution of OCs with respect to Galactocentric distance does not follow the expected exponential profile, instead it falls off both for regions external to the Solar circle and more sharply towards the Galactic center. We simulate the effects of completeness assuming that the observed distribution of the number of OCs with a given number of stars above the background, measured in a restricted zone outside the Solar circle, is representative of the intrinsic distribution of OCs throughout the Galaxy. Two simulation models are considered in which the intrinsic number of observable stars are distributed: (i)assuming the actual positions of the OCs in the sample, and (ii)random selection of OC positions. As a result we derive completeness-corrected radial distributions which agree with exponential disks throughout the observed Galactocentric distance range 5–14 kpc, with scale lengths in the range RD, smaller than those inferred by means of stars. In particular we retrieve the expected exponential-disk radial profile for the highly depleted regions internal to the Solar circle. The smaller values of RDmay reflect intrinsic differences in the spatial distributions of OCs and stars. We derive a number-density of Solar-neighbourhood (with distances from the Sun $\rm\mbox{$d_\odot$}\leq1.3\,kpc$) OCs of $\rm\mbox{$\rm\rho_\odot$}=795\pm70\,kpc^{-3}$, which implies a total number of (Trumpler types I to III) OCs of ${\sim}730$of which ${\sim}47\%$would already have been observed. Extrapolation of the completeness-corrected radial distributions down to the Galactic center indicates a total number of OCs in the range $\rm(1.8{-}3.7)\times10^5$. These estimates are upper-limits because they do not take into account depletion in the number of OCs by dynamical effects in the inner parts of the Galaxy. The observed and completeness-corrected age-distributions of the OCs can be fitted by a combination of two exponential-decay profiles which can be identified with the young and old OC populations, characterized by age scales of ${\sim}100\,\rm Myr$and $\rm{\sim}1.9\,Gyr$, respectively. This rules out evolutionary scenarios based on constant star-formation and OC-disruption rates. Comparing the number of observed embedded clusters and candidates in the literature with the expected fraction of very young OCs, derived from the observed age-distribution function, we estimate that 3.4–8% of the embedded clusters do actually emerge from the parent molecular clouds as OCs.

We present the analysis of deep colour–magnitude diagrams (CMDs) of five rich LMC clusters. The data were obtained with HST/WFPC2 in the F555W(~V) and F814W(~I) filters, reaching $V_{555} \sim 25$. The sample of clusters is composed of NGC 1805 and NGC 1818, the youngest ones ($\tau < 100$Myr), NGC 1831 and NGC 1868, of intermediate-age ($ 400 < \tau < 1000 $Myr), and Hodge 14, the oldest ($\tau > 1200$Myr). We discuss and apply a statistical method for correcting the CMD for sampling incompleteness and field star contamination. Efficient use of the CMD data was made by means of direct comparisons of the observed to model CMDs. The CMD modeling process generates a synthetic Main Sequence (MS), where we introduce as model inputs the information about age, chemical composition, present day mass function (PDMF), fraction of unresolved binaries, distance modulus and light extinction. The photometric uncertainties were empirically determined from the data and incorporated into the model as well. Statistical techniques of CMD comparisons using 1 and 2 dimensions are presented and applied as an objective method to assess the compatibility between model and data CMDs. By modeling the CMDs from the central region we infer the metallicity (Z), the intrinsic distance modulus ($(m-M)_0$) and the reddening value ($E(B-V)$) for each cluster. We also determined the age for the clusters with $\tau > 400$Myr. By means of two-dimensional CMD comparisons we infer the following values: for NGC 1805, $Z=0.007 \pm 0.003$, $(m-M)_{0}=18.50 \pm 0.11$, $E(B-V)=0.03 \pm 0.01$; for NGC 1818, $Z=0.005 \pm 0.002$, $(m-M)_{0}=18.49 \pm 0.14$, $E(B-V) \sim 0.00$; for NGC 1831, $Z=0.012 \pm 0.002$, log($\tau/$yr$)=8.70 \pm 0.03$, $(m-M)_{0}=18.70 \pm 0.03$, $E(B-V) \sim 0.00$; for NGC 1868, $Z=0.008 \pm 0.002$, log($\tau/$yr$)=8.95 \pm 0.03$, $(m-M)_{0}=18.70 \pm 0.03$, $E(B-V) \sim 0.00$; for Hodge 14, $Z=0.008 \pm 0.004$, log($\tau/$yr$)=9.23 \pm 0.10$, $(m-M)_{0}=18.51 \pm 0.13$, $E(B-V)=0.02 \pm 0.02$. Taking into account the uncertainties, these values are in accordance with the ones obtained applying the one-dimensional CMD analysis, adding reliability to these determinations.

We investigate the properties of two stellar concentrations in a low-absorption disk zone in Centaurus, located respectively at $\ell=306.47^{\circ}$, $b=-0.61 ^{\circ}$, and $\ell=307.01^{\circ}$, $b=-0.74 ^{\circ}$. The present analysis is based mostly on 2MASS photometry, as well as optical photometry. Based on colour–magnitude diagrams and stellar radial density profiles, we show that these concentrations are not open star clusters. Instead, they appear to be field stars seen through a differentially-reddened window. We estimate that the bulk of the stars in both stellar concentrations is located at ~1.5 kpc from the Sun, a distance consistent with that of the Sgr-Car arm in that direction. This low-absorption window allows one to probe into distant parts of the disk besides the Sgr-Car arm, probably the tangent part of the Sct-Cru arm, and/or the far side of the Sgr-Car arm in that direction. The main sequence associated to the Sgr-Car arm is reddened by $\mbox{$E(B-V)$}\sim0.5$, so that this window through the disk is comparable in reddening to Baade's window to the bulge. We also investigate the nature of the open cluster candidate Ru 166. The presently available data do not allow us to conclude whether Ru 166 is an actual open cluster or field stars seen through a small-scale low-absorption window.

We present the analysis of a deep colour-magnitude diagram (CMD) of NGC 1831, a rich star cluster in the LMC. The data were obtained with HST/WFPC2 in the F555W (~V) and F814W (~I) filters, reaching $m_{555} \sim 25$. We discuss and apply a method of correcting the CMD for sampling incompleteness and field star contamination. Efficient use of the CMD data was made by means of direct comparisons of the observed to model CMDs. The model CMDs are built by an algorithm that generates artificial stars from a single stellar population, characterized by an age, a metallicity, a distance, a reddening value, a present day mass function and a fraction of unresolved binaries. Photometric uncertainties are empirically determined from the data and incorporated into the models as well. Statistical techniques are presented and applied as an objective method to assess the compatibility between the model and data CMDs. By modelling the CMD of the central region in NGC 1831 we infer a metallicity $Z = 0.012$, $8.75 \leq \log\,(\tau/{\rm yr}) \leq 8.80$, $18.54 \leq (m-M)_{0} \leq 18.68$and $0.00 \leq E(B-V) \leq 0.03$. For the position dependent PDMF slope ($ \alpha = -{\rm d}\log\Phi(M)/{\rm d}\log M$), we clearly observe the effect of mass segregation in the system: for projected distances $R \leq 30$arcsec, $\alpha \simeq 1.7$, whereas $2.2 \leq \alpha \leq 2.5$in the outer regions of NGC 1831.

We built Kband extinction maps in the area of two candidate low-extinction windows in the inner Bulge: W0.2–2.1 at ($\ell,~b$) = (0.25°, -2.15°), and W359.4–3.1 at ($\ell,~b$) = (359.40°, -3.10°). We employed JHKsphotometry from the 2MASS Point Source Catalog. Extinction values were determined by fitting the upper giant branch found in the present 2MASS Ks($J-K_{\rm s}$) diagrams to a de-reddened bulge stellar population reference giant branch. We tested the method on the well known Baade's and Sgr I windows: the 2MASS mean extinction values in these fields agreed well with those of previous studies. We confirm the existence of low-extinction windows in the regions studied, as local minima in the AKmaps reaching AKvalues about 2 standard deviations below the mean values found in the neighbouring areas. Schlegel et al.'s ([CITE]) FIR extinction maps, which integrate dust contributions throughout the Galaxy, are structurally similar to those derived with 2MASS photometry in the two studied windows. We thus conclude that the dust clouds affecting the 2MASS and FIR maps in these directions are basically the same and are located on foreground of the bulk of bulge stars. However, the AKabsolute values differ significantly. In particular, the FIR extinction values for W359.4–3.1 are a factor $\simeq$1.45 larger than those derived from the 2MASS photometry. Possible explanations of this effect are discussed. The lower Galactic latitudes of the low-extinction windows W359.4–3.1 and W0.2–2.1, as compared to Baade's Window, make them promising targets for detailed studies of more central bulge regions.

Photometry in the Band Vbands is presented for the southern stellar groups NGC 1901 and NGC 1252. NGC 1901 is often described as an open cluster while NGC 1252 consists of a concentration of about 20 stars centered ≈20′ north of the original New General Catalogue coordinates, and at the southwest edge of the large region previously assigned to this object in the literature. NGC 1901 has a clear main sequence and shares similarities with the Hyades. We derive a reddening value $E(B-V) = 0.04$, a distance from the Sun $d_{\odot} = 0.45$kpc ($Z = -0.23$kpc) and an age 0.6 ±0.1 Gyr. NGC 1901 is conclusively a physical system, dynamically comparable to or more evolved than the Hyades. The colour-magnitude diagram of NGC 1252 suggests a turnoff and main sequence, and a total of 12 probable members. We simulated the Galactic field colour-magnitude diagram in the same direction and found it to be a poor match to NGC 1252, suggesting that NGC 1252 is not a field fluctuation. Isochrone fitting to the probable members is consistent with $E(B-V) = 0.02$, $d_{\odot} = 0.64$kpc ($Z = -0.46$kpc) and an age 3 ±1 Gyr. NGC 1252 cannot be ruled out as a physical group with the available data. If so, evidence is found that it is not a classical open cluster, but rather an open cluster remnant.

We show the results of deep Vand IHST photometry of 6 rich star clusters in the Large Magellanic Cloud with different ages and metallicities. The number of stars with measured magnitudes in each cluster varies from about 3000 to 10 000 stars. We build stellar density and surface brightness profiles for the clusters and extract half-light radii and other structural parameters for each. We also obtain luminosity functions, $\Phi (M_V)$, down to $M_V \simeq 6$$(M/M_{\odot} \ga 0.9)$, and investigate their dependence with distance from the cluster centre well beyond their half-light radius. In all clusters we find a systematic increase in the luminosity functions slope, $\Delta \log \Phi (M_V) / \Delta (M_V)$, with radial distance from the centre. Among the clusters displaying significant mass segregation are the 2 youngest in the sample: NGC 1805, NGC 1818. For these two clusters we obtain present day mass functions. The NGC 1818 mass function is in excellent agreement with that derived by other authors, also using HST data. The young cluster mass function slopes differ, that of NGC 1805 being systematically steeper than NGC 1818. Since these are very young stellar systems ($\tau \la 40$Myrs), these variations may reflect the initial conditions rather than evolution due to internal dynamics.

We present a list of 34 neglected entries from star cluster catalogues located at relatively high galactic latitudes ($|b| > $15°) which appear to be candidate late stages of star cluster dynamical evolution. Although underpopulated with respect to usual open clusters, they still present a high number density contrast as compared to the galactic field. This was verified by means of (i) predicted model counts from different galactic subsystems in the same direction, and (ii) Guide Star Catalog equal solid angle counts for the object and surrounding fields. This suggests that the objects are physical systems, possibly star clusters in the process of disruption or their fossil remains. The sample will be useful for followup studies in view of verifying their physical nature.

We analyse a sample of over 1000 stars from 32 fields imaged in the Vand Ibands with the Wide Field and Planetary Camera, on board of the Hubble Space Telescope. The fields are located at Galactic latitudes $\vert b \vert \geq 15^{\circ}$and in various directions on the sky. We consider models for the structure of the Galaxy with different choices for the main parameters governing the shape and luminosity function of the thick disk and stellar halo. Comparing model predictions with the observed colour-magnitude diagram we are able to rule out an increasing or flat stellar luminosity function at the low-luminosity end. We also rule out large values of the vertical scale height of the thick disc, z0, finding it to be in the range $800 \leq z_0 \leq 1200$pc. As for the local density normalization, values within the range $4 \% \leq n_0 \leq 8 \%$seem to better reproduce the data. Our data essentially rule out a flattened stellar halo ($c/a \la 0.5$) or models with both large local normalization and effective radii.

Context. Luminous elliptical galaxies generally display a rich star cluster system, whose properties provide strong constraints on the physics of galaxy formation and evolution. Star cluster system studies, however, concentrate on galaxies located in nearby or rich galaxy clusters.Aims. We acquired deep B and I images of NGC?1600, a luminous elliptical in a galaxy group to study its star cluster system. The images were obtained with the Optical Imager at the Southern Telescope for Astrophysical Research for an exposure time of 1.66?h in each filter.Methods. The sample selection incompleteness was assessed as a function of magnitude and image background level. Source counts were measured for different elliptical annuli from the centre of NGC?1600, background subtracted, and fitted with a Gaussian function. Colour distributions were derived as a function of galactocentric distance for sources measured successfully in both filters. Typical ages and metallicities were estimated based on single stellar population models.Results. A clear excess of point sources around NGC?1600 was found in relation to the nearby field. The source counts were consistent with a Gaussian distribution typical of other luminous ellipticals. The luminosity function fits provided an estimate of the density of clusters at the different annuli that could be integrated in solid angle, resulting in an estimated total population of NGC?2850 star clusters. This yielded a specific frequency of SN?1.6. The colour distributions show a hint of bimodality, especially at ?20?kpc from the centre. Clusters in this region may be associated with a ring or shell perturbation. Finally, the star cluster candidates were cross-correlated to discrete X-ray sources and a coincidence rate of ?40% was found. These are likely to be globular clusters harboring low-mass X-ray binaries.

Context. There is a clear scarcity of structural parameters for stellar thick discs, especially for spiral galaxies located in high-density regions, such as galaxy clusters and compact groups.Aims. We have modelled the thin and thick discs of 4 edge-on spirals located in Abell?clusters: NGC?705, ESO?243G49, ESO?187G19, LCSBS?0496P. Deep I?band images of NGC?705 were taken from the HST archive, whereas the remaining images were obtained with the Southern Telescope for Astrophysical Research (SOAR) in Gunn r?filter. They reached surface brightness levels of ?I?26.0?mag?arcsec-2and ?r?26.5?mag?arcsec-2, respectively.Methods. Profiles were extracted from the deep images, in directions both parallel and perpendicular to the major axis. Profile fits were carried out at several positions, yielding horizontal and vertical scale parameters for both thin and thick disc components.Results. The extracted profiles and fitted disc parameters vary from galaxy to galaxy. Two galaxies have a horizontal profile with a strong down-turn at outer radii, preventing a simple exponential from fitting the entire range. For the 2 early-type spirals, the thick discs have larger scalelengths than the thin discs, whereas no trend is seen for the later types. Both the thin and thick discs sampled tend to have similar scalelengths and scaleheights when compared to typical field disc galaxies. However, the thin disc parameters of the 2 farthest galaxies, both late-type spirals, may be significantly affected by seeing effects. Taken at face value, our results suggest that environment plays a minor role in determining the thin and thick disc sizes.

We present the analysis of deep colour–magnitude diagrams (CMDs) of 6 stellar fields in the LMC. The data were obtained using HST/WFPC2 in the $F814W$ (~$I$) and $F555W$ (~$V$) filters, reaching ${V_{555} \sim 26.5}$. We discuss and apply a method of correcting CMDs for photometric incompleteness. A method to generate artificial CMDs based on a model star formation history is also developed. This method incorporates photometric error effects, unresolved binaries, reddening and allows use of different forms of the initial mass function and of the SFH itself. We use the Partial Models Method, as presented by Gallart and others, for CMD modelling, and include control experiments to prove its validity in a search for constraints on the Large Magellanic Cloud star formation history in different regions. Reliable star formation histories for each field are recovered by this method. In all fields, a gap in star formation with $\tau \sim 700$ Myr is observed. Field-to-field variations have also been observed. The two fields near the LMC bar present some significant star forming events, having formed both young ($\tau \la 1$ Gyr) and old ($\tau \ga 10$ Gyr) stars, with a clear gap from $3{-}6$ Gyr. Two other fields display quite similar SFHs, with increased star formation having taken place at $\tau \simeq 2{-}3$ Gyr and $6 \la \tau \la 10$ Gyr. The remaining two fields present star formation histories closer to uniform, with no clear event of enhanced star formation.