We present a picture of star formation around the H ii region Sh2‐235 (S235) based upon data on the spatial distribution of young stellar clusters and the distribution and kinematics of molecular gas around S235. We observed 13CO (1–0) and CS (2–1) emission toward S235 with the Onsala Space Observatory 20‐m telescope and analysed the star density distribution with archival data from the Two Micron All‐Sky Survey (2MASS). Dense molecular gas forms a shell‐like structure at the southeastern part of S235. The young clusters found with 2MASS data are embedded in this shell. The positional relationship of the clusters, the molecular shell and the H ii region indicates that expansion of S235 is responsible for the formation of the clusters. The gas distribution in the S235 molecular complex is clumpy, which hampers interpretation exclusively on the basis of the morphology of the star‐forming region. We use data on kinematics of molecular gas to support the hypothesis of induced star formation, and distinguish three basic types of molecular gas components. The first type is primordial undisturbed gas of the giant molecular cloud, the second type is gas entrained in motion by expansion of the H ii region (this is where the embedded clusters were formed) and the third type is a fast‐moving gas, which might have been accelerated by winds from the newly formed clusters. The clumpy distribution of molecular gas and its kinematics around the H ii region implies that the picture of triggered star formation around S235 can be a mixture of at least two possibilities: the ‘collect‐and‐collapse’ scenario and the compression of pre‐existing dense clumps by the shock wave.

We present a detailed analysis of the spatial distribution of the stellar populations in the Galactic globular cluster ω Centauri. Taking advantage of the large photometric catalogue published by Pancino et al., we confirm that metal‐rich populations have a spatial distribution which is significantly different from the metal‐poor dominant population. In particular (i) the different sub‐populations have different centroids and (ii) the metal‐poor population is elongated along the east–west direction, while the metal‐rich populations are oriented along the orthogonal direction, i.e. north–south. The evidence presented here can partially explain the weird spatial metallicity segregation found by Jurcsik, and further supports the hypothesis that different subpopulations in ω Centauri might have had different origins.

Surface and spatial radial density profiles in open clusters are derived with the use of a kernel estimator method. Formulae are obtained for contribution of every star into spatial density profile. Evaluation of spatial density profiles is tested against open cluster models from N-body experiments with N=500. Surface density profiles are derived for seven open clusters NGC 1502, NGC 1960, NGC 2287, NGC 2516, NGC 2682, NGC 6819 and NGC 6939 by means of 2MASS data and for different limiting magnitudes. The selection of optimal kernel halfwidth is discussed. It is shown that open cluster radius estimates hardly depend on kernel halfwidth. Hints of stellar mass segregation and structural features indicating cluster non-stationarity in the regular force field are found. A comparison with other investigations shows that the data on open cluster sizes are often underestimated. The existence of an extended corona around open cluster NGC 6939 was confirmed. A combined function composed of King density profile for the cluster core and uniform sphere for the cluster corona is shown to be a better approximation of the surface radial density profile. King function alone does not reproduce surface density profiles of sample clusters properly. Number of stars, the cluster masses, and the tidal radii in the Galactic gravitational field for the sample clusters are estimated. It is shown that NGC 6819 and NGC 6939 are extended beyond their tidal surfaces.

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Binary stars are present in all stellar systems, yet their role is far from being fully understood. We investigate the effect of unresolved binaries in the derivation of open clusters' mass by star counts. We start from the luminosity functions of five open clusters: IC 2714, NGC 1912, NGC 2099. Luminosity functions are obtained via star counts extracted from the 2MASS database. The fraction of binaries is considered to be independent on stellar magnitude. We take into account different assumptions for the binary mass ratio distribution and assign binary masses using the so-called luminosity-limited pairing method and Monte-Carlo simulations. We show that cluster masses increase when binary stars are appropriately taken into account.

We present homogeneous V, I CCD photometry of nine stellar fields in the two inner quadrants of the Galactic plane. The lines-of-view to most of these fields aim in the direction of the very inner Galaxy, where the Galactic field is very dense, and extinction is high and patchy. Our nine fields are, according to several catalogs, centred on Galactic star clusters, namely Trumpler 13, Trumpler 20, Lynga 4, Hogg 19, Lynga 12, Trumpler 25, Trumpler 26, Ruprecht 128, and Trumpler 34. Apart from their coordinates, and in some cases additional basic data (mainly from the 2MASS archive), their properties are poorly known. By means of star count techniques and field star decontaminated Color-Magnitude diagrams, the nature and size of these visual over-densities has been established; and, when possible, new cluster fundamental parameters have been derived. To strengthen our findings, we complement our data-set with JHK s photometry from the 2MASS archive, that we analyze using a suitably defined Q-parameter. Most clusters are projected towards the Carina-Sagittarium spiral arm. Because of that, we detect in the Color Magnitude Diagrams of most of the other fields several distinctive sequences produced by young population within the arm. All the clusters are of intermediate or old age. The most interesting cases detected by our study are, perhaps, that of Trumpler 20, which seems to be much older than previously believed, as indicated by its prominent -and double-red clump; and that of Hogg 19, a previously overlooked old open cluster, whose existence in such regions of the Milky Way is puzzling.

We employed recent Gaia/DR2 data to investigate the dynamical status of the nearby (300 pc), old (2.5 Gyr) open cluster Ruprecht 147. We found prominent leading and trailing tails of stars along the cluster orbit, which demonstrates that Ruprecht 147 is losing stars at fast pace. Star counts indicate the cluster has a core radius of 33.3 arcmin and a tidal radius of 137.5 arcmin. The cluster also possesses an extended corona, which cannot be reproduced by a simple King model. We computed the present-day cluster mass using its luminosity and mass function, and derived an estimate of 234 ± 52 M ⊙. We also estimated the cluster original mass using available recipes extracted from N-body simulations obtaining a mass at birth of 50,000 ± 6500 M ⊙. Therefore dynamical mass loss, mostly caused by tidal interaction with the Milky Way, reduced the cluster mass by about 99%. We then conclude that Ruprecht 147 is rapidly dissolving into the general Galactic disk.

Abstract. We present the first results of our interstellar polarization programme for the South Galactic Pole (b < −70• ). The new observations (43 stars) combined with previously published data show that there is a substantial interstellar polarization in this area of the sky. Starting at a distance of 300 pc, we have found stars with P > 0.3% including one for which P ≈ 0.6%. These measurements lead to the conclusion that there is a significant amount of interstellar dust at high south galactic latitudes. Futhermore, there is a remarkable alignment seen over the South Polar Cap: for most stars the directions of polarization vectors are aligned with the longitude l ≈ 80• , close to the expected direction of the global magnetic field. In this respect the SGP seems to differ strongly from its northern counterpart.