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Aims. In this work we derive clues to the formation scenario and ionisation source of the lenticular galaxy NGC 3607 by means of metallicity gradients, stellar population, and emission lines properties.

Context. Passing through the disk of a galaxy, a massive object such as a globular cluster can trigger star formation.

Context. Open clusters older than ~4 Gyr are rare in the Galaxy. Affected by a series of mass-decreasing processes, the stellar content of most open clusters dissolves into the field on a time-scale shorter than ~1 Gyr. In this sense, improving the statistics of old objects may provide constraints for a better understanding of the dynamical dissolution of open clusters.

Context.Structural parameters and the total MVmagnitude are important properties for the characterisation of individual globular clusters. With the growth in statistics, especially of the intrinsically faint objects, the collective properties of the Galactic globular cluster system will be better defined, leading to a deeper understanding of the Galaxy formation processes.

Context.Structural parameters of model star clusters are measured in radial profiles built from number-density, mass-density and surface-brightness distributions, assuming as well different photometric conditions.

Context.We examine the dynamical survival of intermediate-age/old open clusters in the inner Galaxy.

Aims.We investigate the nature of the recently catalogued star cluster candidate FSR 584, which is projected in the direction of the molecular cloud W 3 and may be the nearest globular cluster to the Sun.

Context.Structural and dynamical parameters of faint open clusters are probed with quality 2MASS-photometry and analytical procedures developed for bright clusters.

Aims.We derive accurate parameters related to the CMD, structure and dynamical state of M 52 and NGC 3960, whose fields are affected by differential reddening. Previous works estimated their ages in the ranges $35{-}135$Myr and $0.5{-}1.0$Gyr, respectively.

Aims.We derive the structure, distribution of MS and PMS stars and dynamical state of the young open cluster NGC 4755. We explore the possibility that, at the cluster age, some MS and PMS stars still present infrared excesses related to dust envelopes and proto-planetary discs.

Aims.Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way, such as the distance of the Sun to the Galactic centre, the bulge and halo structural parameters, and cluster destruction rates.Methods.We build a reduced sample that has been decontaminated of all the clusters younger than 10 Gyr and of those with retrograde orbits and/or evidence of relation to dwarf galaxies. The reduced sample contains 116 globular clusters that are tested for whether they were formed in the primordial collapse.Results.The 33 metal-rich globular clusters ($\rm [Fe/H]\geq-0.75$) of the reduced sample basically extend to the Solar circle and are distributed over a region with the projected axial-ratios typical of an oblate spheroidal, $\Delta x:\Delta y:\Delta z\approx1.0:0.9:0.4$. Those outside this region appear to be related to accretion. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios ${\approx}1.0:1.0:0.8$extending from the central parts to the outer halo, although several clusters in the external region still require detailed studies to unravel their origin as accretion or collapse. A new estimate of the Sun's distance to the Galactic centre, based on the symmetries of the spatial distribution of 116 globular clusters, is provided with a considerably smaller uncertainty than in previous determinations using globular clusters, $R_{\rm O}=7.2\pm0.3\,\rm kpc$. The metal-rich and metal-poor radial-density distributions flatten for $R_{\rm GC}\leq2\,\rm kpc$and are represented well over the full Galactocentric distance range both by a power-law with a core-like term and Sérsic's law; at large distances they fall off as ${\sim} R^{-3.9}$.Conclusions.Both metallicity components appear to have a common origin that is different from that of the dark matter halo. Structural similarities between the metal-rich and metal-poor radial distributions and the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse and part was accreted in an early period of merging. This applies to the bulge as well, suggesting an early merger affecting the central parts of the Galaxy. The present decontamination procedure is not sensitive to all accretions (especially prograde) during the first Gyr, since the observed radial density profiles still preserve traces of the earliest merger(s). We estimate that the present globular cluster population corresponds to ${\leq}23\pm6\%$of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law, and Sérsic's law indicates that we are dealing with spheroidal subsystems at all scales.

We present BVIphotometry of the globular cluster NGC 6642 using the SOI imager at the SOAR Telescope. The colour magnitude diagrams (CMD) reach ≈1.5 mag in Vbelow the main sequence turn-off. A comparison of the overall sequences, and in particular the Red Giant Branch slope of NGC 6642 with that of M 5, indicates that the two clusters must have a similar metallicity of [Fe/H] ≈–1.3. We also obtained a reddening $E(B-V)=0.42\pm0.03$for NGC 6642, and a distance from the Sun of $d_{\odot}=7.2\pm0.5$kpc. Therefore NGC 6642 is a moderately metal-poor globular cluster that is spatially located in the bulge at a galactocentric distance of $R_{\rm GC}\approx 1.7$kpc. The comparison of CMDs of NGC 6642 with those of M 5 shows that there is a very good match of magnitude difference between turn-off and horizontal branch, suggesting comparable ages. The age of M 5 is typical of halo globulars, so NGC 6642 is coeval with the halo. It is a good candidate as one of the few genuine metal-poor and old bulgeclusters, and might be one of the oldest fossils in the Galaxy.

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 use J, Hand KS2MASS 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 ≈$5\,\mbox{$M_\odot$}$. Based on the fraction of KSexcess stars in the colour–colour diagram we estimate an age of $1.3\pm0.3$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 $\mbox{$d_\odot$}=1.8\pm0.5\,\rm kpc$. The radial density distribution including MS and PMS stars is fitted by a King profile with a core radius Rcore. The cluster density profile merges into the background at a limiting radius Rlim. From the field-star subtracted luminosity functions we derive the mass functions (MFs) in the form $\phi(m)\propto m^{-(1+\chi)}$. In the halo and through the whole cluster the MFs have slopes $\rm\chi=1.52\pm0.13$and $\rm\chi=1.45\pm0.12$, respectively, thus slightly steeper than Salpeter's IMF. In the core the MF is flat, $\rm\chi=0.62\pm0.16$, indicating some degree of mass segregation since the cluster age is a factor ~2 larger than the relaxation time. Because of the very young age of NGC 6611, part of this effect appears to be related to the molecular cloud-fragmentation process itself. We detect $362\pm120$PMS stars. The total observed mass including detected MS (in the range $5{-}85\,\mbox{$M_\odot$}$) and PMS stars amounts to ~$1600\,\mbox{$M_\odot$}$, thus more massive than the Trapezium cluster. Compared to older open clusters of different masses, the overall NGC 6611 fits in the relations involving structural and dynamical parameters. However, the core is atypical in the sense that it looks like an old/dynamically evolved core. Again, part of this effect must be linked to formation processes.

We derive photometric, structural and dynamical evolution-related parameters of five as yet unstudied low-contrast open clusters located in the third quadrant using 2MASS data. The target clusters are Czernik 31, Czernik 32, Haffner 9, Haffner 11 and Trumpler 13. We apply a statistical field-star decontamination procedure to infer on the intrinsic colour–magnitude diagram (CMD) morphology which is critical for such low-contrast objects. Consequently, it became possible to derive accurate reddening, age, distance from the Sun and Galactocentric distance for the five clusters. In the structural and luminosity/mass-function analyses we apply a colour-magnitude filter which encompasses the cluster evolutionary CMD sequences and excludes stars with discrepant colours. Using this procedure we derive core and limiting radii, mass function (MF) slope, total mass, mass density and relaxation time. We derive ages in the range 140–1100 Myr, Galactocentric distances within 7.7–11.4 kpc, and total masses within 360–2900 $M_\odot$. Reflecting large-scale mass segregation, the MF slope in the core is significantly flatter than that in the halo of the five clusters. Although some of the present clusters are relatively younger than the Gyr-old clusters, they present evidence of advanced dynamical evolution. This kind of study has become possible because of the photometric uniformity and spatial coverage of 2MASS which allows a proper subtraction of the field-star contamination on the target CMDs. The present study indicates that low-contrast clusters can be studied with 2MASS, particularly after field-star subtraction, which is important since most of the unstudied open clusters belong to this class.

An overall analysis of the structure and stellar content of M 11 is presented, thanks to the wide-angle 2MASS spatial coverage. We derive photometric and structural parameters and discuss the spatial dependance of the luminosity and mass functions. Photometric parameters basically agree with previous ones mostly based on the optical. We obtained a core radius of 1.23 pc and a tidal radius of 29 pc. In particular, the cluster is populous enough so that the tidal radius could be obtained by fitting the three-parameter King profile to the radial distribution of stars. We analyzed the spatial distribution of mass functions, finding that the slope changes from -0.73 in the core to +2.88 in the outer halo. The spatial distribution of mass function slopes derived from 2MASS agrees with that derived from optical CCD data, which further confirms the reliability of 2MASS data for future analyses of this kind at comparable observational limits. We detect mass segregation up to distances from the center of ≈$20\arcmin$. We emphasize that the mass function slope in the core is flatter than anywhere else as a consequence of mass segregation. The derived total cluster mass is ≈$11\,000\,\mbox{$M_\odot$}$.

Luminosity and mass functions in the old open cluster NGC 188 are analysed by means of Jand H2MASS photometry, which provides uniformity and spatial coverage for a proper background subtraction. With an age of about 6–8 Gyr, NGC 188 is expected to be suffering the effects of advanced dynamical evolution. Indeed, previous works in optical bands have suggested the presence of mass segregation. Within the uncertainties, the observed projected radial density profile of NGC 188 departs from the two-parameter King model in two inner regions, which reflects the non-virialized dynamical state and possibly, some degree of non-sphericity in the spatial shape of this old open cluster. Fits with two and three-parameter King models to the radial distribution of stars resulted in a core radius Rcorepc and a tidal radius Rtidalpc, about twice as large as the visual limiting radius. The concentration parameter $c=1.2\pm0.1$of NGC 188 makes this open cluster structurally comparable to the loose globular clusters. The present 2MASS analysis resulted in significant slope variations with distance in the mass function $\phi(m)\propto m^{-(1+\chi)}$, being flat in the central parts ($\chi=0.6\pm0.7$) and steep in the cluster outskirts ($\chi=7.2\pm0.6$). The overall mass function has a slope $\chi=1.9\pm0.7$, slightly steeper than a standard Salpeter mass function. In this context, NGC 188 is similar to the 3.2 Gyr, dynamically evolved open cluster M 67. Solar metallicity Padova isochrone fits to the near-infrared colour-magnitude diagram of NGC 188 resulted in an age of $7.0\pm1.0$Gyr. The best fit, obtained with the 7.1 Gyr isochrone, produced a distance modulus $\mbox{$(m-M)_0$}=11.1\pm0.1$, $\mbox{$E(B-V)$}=0.0$, and a distance to the Sun $\mbox{$d_\odot$}=1.66\pm0.08$kpc. The observed stellar mass (in the range $0.98\,\mbox{$M_\odot$}{-} 1.08\,\mbox{$M_\odot$}$) in NGC 188 is mobs. A simple extrapolation of the observed overall mass function to stars with $0.08\,\mbox{$M_\odot$}$resulted in a total present mass of mtot. On the other hand, for a more realistic initial mass function which flattens in the low-mass range, the total mass in NGC 188 drops to mtot. Since mass-loss processes such as evaporation and tidal stripping have been occurring in this old open cluster for about 7 Gyr, the primordial mass in NGC 188 must have been significantly larger than ${\sim}4\times10^3\,\mbox{$M_\odot$}$. We also examined the consequences of the presence of unresolved binaries and concluded that, even if dominant in the CMD, binaries alone are not responsible for the flat central mass function, which supports the mass-segregation scenario.

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 analyze 9 open clusters with ages in the range 70 Myr to 3.2 Gyr using UCAC2 proper motion data and 2MASS photometry, which allows us to reach stellar masses down to ${\approx}0.7\,\mbox{$M_\odot$}$. We employ in this work an approach in which the background proper motion contribution is statistically subtracted in order to obtain the cluster's intrinsic proper motion distribution. For each cluster we consider the projected velocity distributions in the core and off-core regions separately. In the projected velocity distribution of all sample clusters we find a well-defined low-velocity peak, as well as an excess in the number of stars at larger velocities. The low-velocity peak is accounted for by the random motion of the single stars, while the high-velocity excess can be attributed to the large velocity changes produced by a significant fraction of unresolved binaries in a cluster. We derive kinematic parameters of the single-star distribution, in particular the projected velocity dispersion. The relatively large velocity dispersions derived in this work may reflect the non-virialized state of the clusters. Based on the relative number of high-velocity (binary) and single stars, we inferred for the sample clusters unresolved binary fractions in the range fbin, for both core and off-core regions. Stars with a projected velocity exceeding the maximum reached by the single-star distribution are identified in 2MASS Jcolour–magnitude diagrams. The asymmetry observed in the distribution of these stars around the main sequence is consistent with models of main-sequence widening resulting from unresolved binaries combined with 2MASS photometric uncertainties. The present results suggest that care must be taken when applying proper-motion filters to sort out members, especially binaries in a star cluster. This paper shows that proper motions turn out to be a useful tool for identifying high-velocity stars as unresolved binary cluster members, and as a consequence, map and quantify the binary component in colour–magnitude diagrams.

The spatial dependence of luminosity and mass functions of evolved open clusters is discussed in this work using Jand H2MASS photometry, which allows a wide spatial coverage and proper background determination. The target objects are the intermediate-age open cluster NGC 3680 ($\ell=286.76^\circ$and $b=16.92^\circ$), which has been reported as being in an advanced state of dissolution, and NGC 2180 ($\ell=203.85^\circ$, $b=-7.01^\circ$), a possible dynamically evolved open cluster. At the $1-\sigma$level, NGC 2180 presents a radial distribution of stars that can be represented by a King law. We conclude that, although in an advanced dynamical state (mass segregated), NGC 3680 does not present strong signs of dissolution, having luminosity and mass functions very similar to those of the $\mbox{$\tau_{{\rm age}}$}\approx3.2$Gyr open cluster M 67. On the other hand, NGC 2180 appears to have flat, eroded luminosity functions throughout its structure, suggesting that in addition to mass segregation, Galactic tidal stripping has been effective in depleting this object. Accordingly, NGC 2180 may be the missing link between evolved open clusters and remnants. For NGC 2180 we infer a distance to the Sun $\mbox{$d_\odot$}=0.91$±0.15 kpc, an age $\mbox{$\tau_{{\rm age}}$}\approx710$Myr and an observed stellar mass of $\mbox{$m_{{\rm obs}}$}\sim47~\mbox{$M_\odot$}$. For NGC 3680 we derive an age $\mbox{$\tau_{{\rm age}}$}\approx1.6$Gyr, $\mbox{$E(B-V)$}=0.0$and $\mbox{$d_\odot$}=1.00$±0.09 kpc, confirming previous estimates. The observed stellar mass $\mbox{$m_{{\rm obs}}$}\approx130~\mbox{$M_\odot$}$agrees with previous values. We study both clusters in the context of dynamical states estimated from diagnostic diagrams involving photometric and structural parameters. Both objects appear to be dynamically evolved systems. In particular, NGC 2180 is closer to open cluster remnants than NGC 3680.

We report the discovery of three optical open clusters in the Milky Way. Two clusters are in Scutum (Cluster 1 at $\ell=18.44^{\circ}$and $b=-0.42^\circ$, and Cluster 2 at $\ell=19.60^{\circ}$and $b=-1.02^\circ$), thus projected not far from the Galactic center direction, and the other is in Canis Major (Cluster 3 at $\ell=235.61^{\circ}$and $b=-4.10^\circ$), near the anti-center direction. Cluster 3 is less populous than Clusters 1 and 2, but presents evidence of being a physical system. The objects were found optically by inspecting maps obtained from the Guide Star Catalogue and images from the Digitized Sky Survey. No previous identification of a cluster has been reported in any of these areas so far. The analysis was carried out with 2MASS photometry in Jand H. For Cluster 1 we derive an age of $t=25$±5 Myr, a reddening $\mbox{$E(B-V)$}=2.18$±0.03 and a distance from the Sun $\mbox{$d_\odot$}=1.64$±0.19 kpc; for Cluster 2, $t=500$±100 Myr, $\mbox{$E(B-V)$}=0.91$±0.03 and $\mbox{$d_\odot$}=2.19$±0.21 kpc; finally for Cluster 3, $t=32{-}100$Myr, $\mbox{$E(B-V)$}=0.94$±0.03 and $\mbox{$d_\odot$}=3.93$±0.35 kpc. Luminosity and mass functions are derived for Clusters 1 and 2 which, in turn, allow us to estimate their observed masses as $147~\mbox{$M_\odot$}$and $89~\mbox{$M_\odot$}$, respectively. Estimated total masses, by extrapolating the mass functions to $0.08~\mbox{$M_\odot$}$, amount to $382~\mbox{$M_\odot$}$and $614~\mbox{$M_\odot$}$for the two clusters. Cluster 3 has an observed mass of ~$55~\mbox{$M_\odot$}$. The present results indicate that further searches in the optical might still reveal new open clusters, especially in the infrared bands.

We present mid-IR photometric properties for a sample of 28 early-type galaxies observed at 6.75, 9.63 and 15 $\mu{} $m with the ISOCAM instrument on board the ISO satellite. We find total mid-IR luminosities in the range $(3{-}42) \times{} 10^{8}$$ L_{\odot}$. The spectral energy distributions (SED) of the galaxies were derived using the mid-IR data together with previously published UV, optical and near-IR data. These SEDs clearly show a mid-IR emission coming from dust heated at $T \simeq 260$K. Dust grains properties are inferred from the mid-IR colors. The masses of the hot dust component are in the range $10{-}400$$M_{\odot}$. The relationship between the masses derived from mid-IR observations and those derived from visual extinction are discussed. The possible common heating source for the gas and dust is investigated through the correlations between ${\rm H}\alpha$and mid-IR luminosities.

Optical spectra were used to study the stellar population and gas emission, when present, in the central parts of the elliptical galaxies NGC$ $6958, NGC$ $6851 and ESO$ $185-G54, and the spiral galaxies NGC$ $5757, NGC$ $7412 and IC$ $4214. Stellar population properties were derived by comparing the equivalent widths of the absorption lines with those of galaxy templates built from star clusters, as well as by applying a method of stellar population synthesis based on the same star clusters. For the galaxies with emission lines, the underlying stellar population was subtracted to obtain the pure emission spectrum, and the resulting emission line intensities were measured to determine the mechanism responsible for the gas excitation. From this analysis we concluded that the galaxies have solar metallicity except the elliptical ESO$ $185-G54 that reached metallicity slightly above solar. The three ellipticals and the Sa galaxy IC$ $4214 have their nuclei dominated by old stellar populations, although IC$ $4214 appears to have some contribution from the young generation stars. Recent star formation ($t < 500$Myr) is prominent in the nucleus of the SBb galaxy NGC$ $5757, and is also present to a lesser degree in the Sbc NGC$ $7412. In these two galaxies, the recent star formation is responsible for the observed Hiitype emission lines, while IC$ $4214 has LINER emission. Among the ellipticals, only in NGC$ $6958 did we detect ionized gas, whose spectra is typical of LINERs.

Aims. Astrophysical parameters (age, reddening, distance, core and cluster radii) of 14?open clusters (OCs) projected close to the Galactic plane are derived with 2MASS photometry. The OCs are Be?63, Be?84, Cz?6, Cz?7, Cz?12, Ru?141, Ru?144, Ru?172, FSR?101, FSR?1430, FSR?1471, FSR?162, FSR?178, and FSR?198. The OCs Be?63, Be?84, Ru?141, Ru?144, and Ru?172 are studied in more detail than in previous works, while the others have astrophysical parameters derived for the first time.Methods. We analyse the colour-magnitude diagrams (CMDs) and stellar radial density profiles (RDPs) built after field-star decontamination and colour-magnitude filtered photometry. Field-star decontamination is applied to uncover the cluster's intrinsic CMD?morphology, and colour-magnitude filters are used to isolate stars with a high probability of being cluster members in view of structural analyses.Results. The open clusters of the sample are located at d?=1.6-7.1?kpc from the Sun and at Galactocentric distances 5.5-11.8?kpc, with age in the range 10?Myr to 1.5?Gyr and reddening?E(B-V) in the range 0.19-2.56?mag. The core and cluster radii are in the range 0.27-1.88?pc and 2.2-11.27?pc, respectively. Cz?6 and FSR?198 are the youngest OCs of this sample, with a population of pre-main sequence (PMS) stars, while FSR?178 is the oldest cluster.

Context. Usually, a loose stellar distribution can be classified as an OB?stellar group, an association, or a young open cluster. We compare data with the typical OB?association Vul?OB1.Aims. Here, we discuss the nature of Bochum?1, a typical example of an object affected by the above classification problem.Methods. Field-decontaminated 2MASS photometry is used to analyse colour?magnitude diagrams (CMDs) and stellar radial density profiles (RDPs) of the structures present in the region of Bochum?1.Results. The field-decontaminated CMD of Bochum?1 shows main sequence?(MS) and pre-main sequence?(PMS) stars. We report two new small angular-size, compact young clusters and one embedded cluster in the area of Bochum?1. Vul?OB1 harbours the young open cluster NGC?6823 and the very compact embedded cluster Cr?404. The Vul?OB1 association includes the H?II region Sh2-86, and its stellar content is younger (?3?Myr) than that of Bochum?1 (?9?Myr), which shows no gas emission. Bochum?1 harbours one of the newly found compact clusters as its core. The RDP of Bochum?1 is irregular and cannot be fitted by a King-like profile, which suggests significant erosion or dispersion of stars from a primordial cluster. Similarly to Bochum?1, the decontaminated?CMD of NGC?6823 presents conspicuous?MS and PMS sequences. Taken separately, RDPs of MS and PMS stars follow a King-like profile. The core shows an excess density of MS?stars that mimics the profile of a post-core collapse cluster. At such a young age, it can be explained by an excess of stars formed in the prominent core.Conclusions. The present study suggests that Bochum?1 is a star cluster fossil remain that might be dynamically evolving into an OB association. Bochum?1 may be a missing link connecting early star cluster dissolution with the formation of low-mass OB associations.

Context. We investigate the nature of a sample of star cluster candidates detected as stellar overdensities towards the Galactic anticentre.Aims. Taken from the catalogue of Froebrich, Scholz, and Raftery (FSR), the sample contains 28 star cluster candidates located within |??|=20?of the anticentre. These are all the candidates in that sector classified by FSR with a high probability of being star clusters. Our main goals are to determine the fraction of such candidates that are unknown star clusters, to derive their astrophysical parameters, and to investigate the relationship of cluster parameters with position in the Galaxy.Methods. Properties of the star cluster candidates are investigated with field-star decontaminated 2MASS colour?magnitude diagrams and stellar radial density profiles.Results. All candidates present significant excesses in the radial density profiles, consistent with the method from which they were originally selected. Of the 28?candidates, 7 are previously known open clusters, 2 have been recently identified, and 6 are new ones with ages from 30?Myr to 1?Gyr. Among the remaining 13?candidates, 6 are uncertain cases that require deeper observations, while 7 appear to be important field fluctuations. The structure of part of the newly identified open clusters appears to be affected by interaction with giant molecular clouds in the Local and Perseus arms.Conclusions. When photometric and radial distribution properties are considered together, an important fraction of the stellar overdensities with a fluctuation level ?3? are shown to be star clusters. Thus, catalogues of star cluster candidates, coupled to the present kind of study, are an important source for identifying unknown open clusters. Such efforts affect the understanding of the star-formation rate, cluster dynamical evolution, and Galactic structure, among others.

Context. The LMC and SMC are rich in binary star clusters, and some mergers are expected. It is thus important to characterise single clusters, binary clusters and candidates for mergers.Aims. We selected a sample of star clusters in each Cloud with this aim. Surface photometry of 25?SMC and 22?LMC star clusters was carried with the ESO Danish 1.54?m telescope. 23?clusters were observed for the first time for these purposes.Methods. We fitted Elson, Fall and Freeman (EFF) profiles to the data, deriving structural parameters, luminosities and masses. We also use isophotal maps to constrain candidates for cluster interactions.Results. The structural parameters, luminosities and masses presented good agreement with those in the literature. Three binary clusters in the sample have a double profile. Four clusters (NGC?376, K?50, K?54 and NGC?1810) do not have companions and present important deviations from EFF?profiles.Conclusions. The present sample contains blue and red Magellanic clusters. Profiles with excess with respect to EFF were detected in some blue clusters. We find evidence that important deviations from the body of EFF?profiles might be used as a tool to detect cluster mergers.

Context.VISTA Variables in the Vía Láctea (VVV) is one of the six ESO Public Surveys operating on the new 4-m Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of differentages.

Context.Poorly-populated star clusters may have photometric and structural properties not much different from asterisms, to the point that, in some cases, widely-used databases present conflicting classifications.Aims.We investigate the nature of a sample of challenging targets that have been classified either as star clusters or asterisms in different studies. A few objects are studied for the first time.Methods.The analysis employs 2MASS photometry, field-star decontamination, to enhance the intrinsic colour–magnitude diagram (CMD) morphology, and colour-magnitude filters, for high contrast stellar radial density profiles (RDPs).Results.Based on properties derived from field-star decontaminated CMDs, and structural parameters from RDPs, we find that Pismis 12, IC 1434, Juchert 10, Ruprecht 30, NGC 3519, Herschel 1, Mayer 1, and Muzzio 1 are open clusters with ages within 5 Myr − 1.3 Gyr. Ruprecht 129, 130, 140, and 146 are borderline cases, being rather poorly-populated, with evolutionary sequences and RDPs suggesting star clusters. Dolidze 39, BH 79, and Ruprecht 103, have CMDs and RDPs typical of asterisms. Conclusions.When a low stellar population is associated with a dense field contamination and/or important differential reddening, only a thin line separates star clusters and asterisms. These cases require specific analytical tools to establish their nature.