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Register a new userCCD Washington photometry of 10 open clusters or candidates projected close to the Galactic plane
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We present high-quality CCD photometry in the Washington system C and T1 passbands down to T1 ~ 19.5 mag in the fields of 10 Galactic open clusters (OCs) or candidates projected close to the Galactic plane, namely: ESO 313-SC03, BH 54, Ruprecht 87, ESO 129-SC32, BH 217, Collinder 347, Basel 5, Ruprecht 144, Archinal 1 and Berkeley 82. Four of these objects are located toward the Galactic centre direction within a solid angle of 21 deg. No photoelectric or CCD photometry in the optical domain has been so far reported for five of these objects. Cluster radii are estimated from radial density profiles (RDPs) in the cluster fields. Using the cluster Washington (C-T1,T1) colour-magnitude diagrams (CMDs), statistically cleaned from field star contamination, we estimate reddening, heliocentric distance and age of the clusters by fitting Padova theoretical isochrones computed for the Washington system. In all cases, the best fittings were obtained with nearly solar metal content isochrones. Both RDPs and CMDs show that we are dealing with real OCs, except for Ruprecht 87 and Archinal,1 that are found to be probably not physical systems. Differential reddening appears to be present across the fields of ESO313-SC03, ESO129-SC32, BH 217, Collinder 347 and Basel 5. The studied OCs are located at d = 1.0-5.0 kpc from the Sun and at Galactocentric distances R_GC = 6.0-10.6 kpc, with mean reddening E(B-V) in the range 0.10-1.30 mag and ages between 5 Myr (Collinder 347) and ~ 1000 Myr (Basel 5). The estimated linear cluster radii are in the range of 0.4-3.2 pc. In general terms, the results obtained show fairly good agreement with previous photometric results. In some clusters, however, considerable differences are found between the present results and previous ones determined using near-infrared photometric data. The current study provides new OC parameters and some revisions to the OC catalogues.
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Complementing our Washington photometric studies on Galactic open clusters (OCs), we now focus on four poorly studied OCs located in the first and fourth Galactic quadrants, namely BH 84, NGC 5381, BH 211 and Czernik 37. We have obtained CCD photometry in the Washington system $C$ and $T_1$ passbands down to $T_1$ $sim$ 18.5 magnitudes for these four clusters. Their positions and sizes were determined using the stellar density radial profiles. We derived reddening, distance, age and metallicity of the clusters from extracted $(C-T_1,T_1)$ color-magnitude diagrams (CMDs), using theoretical isochrones computed for the Washington system. There are no previous photometric data in the optical band for BH 84, NGC 5381 and BH 211. The CMDs of the observed clusters show relatively well defined main sequences, except for Czernik 37, wherein significant differential reddening seems to be present. The red giant clump is clearly seen only in BH 211. For this cluster, we estimated the age in (1000$^{+260}_{-200}$) Myr, assuming a metallicity of $Z$ = 0.019. BH 84 was found to be much older than it was previously believed, while NGC 5381 happened to be much younger than previously reported. The heliocentric distances to these clusters are found to range between 1.4 and 3.4 kpc. BH 84 appears to be located at the solar galactocentric distance, while NGC 5381, BH 211 and Czernik 37 are situated inside the solar ring.
We present BVI photometry for poorly known southern hemisphere open clusters: NGC 2425, Haffner 10 and Czernik 29. We have calculated the density profile and established the number of stars in each cluster. The colour-magnitude diagrams of the objects show a well-defined main sequence. However, the red giant clump is present only in NGC 2425 and Haffner 10. For these two clusters we estimated the age as 2.5 +/- 0.5 Gyr assuming metallicity of Z=0.008. The apparent distance moduli are in the ranges 13.2<(m-M)_V<13.6 and 14.3<(m-M)_V<14.7, while heliocentric distances are estimated to be 2.9<d<3.8 kpc and 3.1<d<4.3 kpc, respectively for NGC 2425 and Haffner 10. The angular separation of 2.4 deg (150 pc at mean distance) may indicate a common origin of the two clusters.
We present BVI CCD photometry of 10 northern open clusters, Berkeley 43, Berkeley 45, Berkeley 47, NGC 6846, Berkeley 49, Berkeley 51, Berkeley 89, Berkeley 91, Tombaugh 4 and Berkeley 9, and estimate their fundamental parameters. Eight of the clusters are located in the first galactic quadrant and 2 are in the second. This is the first optical photometry for 8 clusters. All of them are embedded in rich galactic fields and have large reddening towards them (E(B-V) = 1.0 - 2.3 mag). There is a possibility that some of these difficult-to-study clusters may be asterisms rather than physical systems, but assuming they are physical clusters, we find that 8 of them are located beyond 2 kpc, and 6 clusters (60% of the sample) are located well above or below the Galactic plane. Seven clusters have ages 500 Myr or less and the other 3 are 1 Gyr or more in age. This sample of clusters has increased the optical photometry of clusters in the second half of the first galactic quadrant, beyond 2 kpc, from 10 to 15. NGC 6846 is found to be one of the most distant clusters in this region of the Galaxy.
The stellar content of Galactic open clusters is gradually depleted during their evolution as a result of internal relaxation and external interactions. The final residues of the evolution of open clusters are called open cluster remnants, barely distinguishable from the field. We aimed to characterise and compare the dynamical states of a set of 16 such objects. The sample also includes 7 objects that are catalogued as dynamically evolved open clusters. We used photometric data from the 2MASS, astrometric data from the GAIA DR2 and a decontamination algorithm that was applied to the three-dimensional astrometric space of proper motions and parallaxes for stars in the objects areas. The luminosity and mass functions and total masses for most open cluster remnants are derived here for the first time. Our analysis used predictions of N-body simulations to estimate the initial number of stars of the remnants from their dissolution timescales. The investigated open cluster remnants present masses and velocity dispersions within well-defined ranges: M between ~10-40M_Sun and sigma_v between ~1-7km/s. Some objects in the remnant sample have a limiting radius R_lim<~2pc, which means that they are more compact than the investigated open clusters; other remnants have R_lim between ~2-7pc, which is comparable to the open clusters. We suggest that the open cluster NGC2180 is entering a remnant evolutionary stage. In general, our clusters show signals of depletion of low-mass stars. This confirms their dynamically evolved states. We conclude that the open cluster remnants we studied are in fact remnants of initially very populous open clusters (No~10^3-10^4 stars). The outcome of the long-term evolution is to bring the final residues of the open clusters to dynamical states that are similar to each other, thus masking out the memory of the initial formation conditions of star clusters.
We carried out a search for new infrared star clusters, stellar groups and candidates using WISE images, which are very sensitive to dust emission nebulae. We report the discovery of 437 embedded clusters and stellar groups that show a variety of structures, both in the stellar and nebular components. Pairs or small groupings of clusters are observed, suggesting multiple generations at the early formation stages. The resulting catalogue provides Galactic and equatorial coordinates, together with angular sizes for all objects. The nature of a representative test sub-sample of 14 clusters is investigated in detail by means of 2MASS photometry. The colour magnitude diagrams and radial density distributions characterize them as stellar clusters. The 437 new objects were found in the ranges $145^circ,leq,ell,leq 290^circ$ and $-25^circ,leq,b,leq 20^circ$, and they appear to be a major object source for future studies of star cluster formation and their early evolution. WISE is a powerful tool to further probe for very young clusters throughout the disk.
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