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We report our study of features at the observed red end of the white dwarf cooling sequences for three Galactic globular clusters: NGC 6397, 47 Tucanae and M 4. We use deep colour- magnitude diagrams constructed from archival Hubble Space Telescope (Advanced Camera for Surveys) to systematically investigate the blue turn at faint magnitudes and the age determinations for each cluster. We find that the age difference between NGC 6397 and 47 Tuc is 1.98+0.44 -0.26 Gyr, consistent with the picture that metal-rich halo clusters were formed later than metal-poor halo clusters. We self-consistently include the effect of metallicity on the progenitor age and the initial-to-final mass relation. In contrast with previous investigations that invoked a single white dwarf mass for each cluster, the data show a spread of white dwarf masses that better reproduce the shape and location of the blue turn. This effect alone, however, does not completely reproduce the observational data - the blue turn retains some mystery. In this context, we discuss several other potential problems in the models. These include possible partial mixing of H and He in the atmosphere of white dwarf stars, the lack of a good physical description of the collision-induced absorption process and uncertainties in the opacities at low temperatures. The latter are already known to be significant in the description of the cool main sequence. Additionally, we find that the present-day local mass function of NGC 6397 is consistent with a top-heavy type, while 47 Tuc presents a bottom-heavy profile. [ABSTRACT FROM AUTHOR]

Molecular clouds at very high latitude (b > 60°) away from the Galactic plane are rare and in general are expected to be non-star-forming. However, we report the discovery of two embedded clusters (Camargo 438 and Camargo 439) within the high-latitude molecular cloud HRK 81.4-77.8 using WISE. Camargo 439 with Galactic coordinates ℓ = 81°.11 and b = -77°. 84 is an ~2 Myr embedded cluster (EC) located at a distance from the Sun of CLQ = 5.09 ± 0.47 kpc. Adopting the distance of the Sun to the Galactic Centre R8857; = 7.2 kpc, we derive for Camargo 439 a Galactocentric distance of RGC = 8.70 ± 0.26 kpc and a vertical distance from the plane of -4.97 ± 0.46 kpc. Camargo 438 at ℓ = 79°.66 and b = -78&#176.86 presents similar values. The derived parameters for these two ECs put HRK 81.4-77.8 in the halo at a distance from the Galactic Centre of ~8.7 kpc and ~5.0 kpc from the disc. Star clusters provide the only direct means to determine the high-latitude molecular cloud distances. The present study shows that the molecular cloud HRK 81.4-77.8 is currently forming stars, apparently an unprecedented event detected so far among high-latitude clouds. We carried out a preliminary orbit analysis. It shows that these ECs are the most distant known ECs from the plane and both cloud and clusters are probably falling ballistically from the halo on to the Galactic disc, or performing a flyby. [ABSTRACT FROM AUTHOR]

We employed field star decontaminated Two Micron All Sky Survey photometry to study four nearby optical embedded clusters -- Collinder 34, NGC 3293, NGC 3766 and NGC 6231 -- obtaining deep colour-magnitude diagrams and stellar radial density profiles. We found what seem to be pre-main sequences detached in different amounts from main sequences in these diagrams. The structural analysis of each cluster revealed different radial distributions for these two sequences. We argued that the detached evolutionary sequences in our sample may be evidence of sequential star formation. Finally, we compared the sample cluster parameters with those of other young clusters in the literature and point out evidence that NGC 3766 and NGC 6231 might be evolving to OB associations. [ABSTRACT FROM AUTHOR]

Andrews-Lindsay 1 is a pertinent open cluster because it may host the planetary nebula (PN) PHR 1315-6555, yet ambiguities linger concerning its fundamental parameters (>50% scatter). New multiband BVJHW1-4 photometry for cluster and field stars, in concert with observations of recently discovered classical Cepheids, were used to constrain the reddening and velocity-distance profiles along the sightline. That analysis yielded the following parameters for the cluster: E(J − H) = 0.24 ± 0.03, d = 10.0 ± 0.4 kpc (dJH = 9.9 ± 0.6 kpc, dBV = 10.1 ± 0.5 kpc), and log τ = 8.90 ± 0.15. The steep velocity-distance gradient along ℓ ~ 305° indicates that two remote objects sharing spatial and kinematic parameters (i.e., PHR 1315-6555 and Andrews-Lindsay 1) are associated, thus confirming claims that the PN is a cluster member. The new distance for PHR 1315-6555 is among the most precise established yet for a Galactic PN (σ/d = 4%). [ABSTRACT FROM AUTHOR]

Context. Fundamental parameters characterizing the end-state of intermediate-mass stars may be constrained by discovering planetary nebulae (PNe) in open clusters (OCs). Cluster membership may be exploited to establish the distance, luminosity, age, and physical size for PNe, and the intrinsic luminosity and mass of its central star. Aims. Four potential PN-OC associations were investigated to assess the cluster membership for the PNe. Methods. Radial velocities were measured from intermediate-resolution optical spectra, complemented with previous estimates in the literature. When the radial velocity study supported the PN/OC association, we analyzed whether other parameters (e.g., age, distance, reddening, central star brightness) were consistent with this conclusion. Results. Our measurements imply that the PNe VBe 3 and HeFa 1 are not members of the OCs NGC5999 and NGC6067, respectively, and that they very likely belong to the background bulge population. Conversely, consistent radial velocities indicate that NGC2452/NGC 2453 could be associated, but our results are not conclusive so additional observations are warranted. Finally, we demonstrate that all the available information point to He 2-86 being a young, highly internally obscured PN member of NGC4463. New near-infrared photometry acquired via the Vista Variables in the Via Lactea ESO public survey was used in tandem with existing UBV photometry to measure the distance, reddening, and age of NGC4463, finding d = 1.55 ± 0.10 kpc, E(B - V) = 0.41 ± 0.02, and t = 65 ± 10 Myr, respectively. The same values should be adopted for the PN if the proposed cluster membership is confirmed. [ABSTRACT FROM AUTHOR]

Cepheids are key to establishing the cosmic distance scale. Therefore it's important to assess the viability of QZ Nor, V340 Nor, and GU Nor as calibrators for Leavitt's law via their purported membership in the open cluster NGC 6067. The following suite of evidence confirms that QZ Nor and V340 Nor are members of NGC 6067, whereas GU Nor likely lies in the foreground: (i) existing radial velocities for QZ Nor and V340 Nor agree with that established for the cluster ( $-39.4\pm0.2(\sigma_{\bar {x}}) \pm1.2 (\sigma)~\mbox{km/s}$) to within 1 km/s, whereas GU Nor exhibits a markedly smaller value; (ii) a steep velocity-distance gradient characterizes the sight-line toward NGC 6067, thus implying that objects sharing common velocities are nearly equidistant; (iii) a radial profile constructed for NGC 6067 indicates that QZ Nor is within the cluster bounds, despite being 20′ from the cluster center; (iv) new BVJH photometry for NGC 6067 confirms the cluster lies d=1.75±0.10 kpc distant, a result that matches Wesenheit distances computed for QZ Nor/V340 Nor using the Benedict et al. (Astron. J. 133:1810, , HST parallaxes) calibration. QZ Nor is a cluster Cepheid that should be employed as a calibrator for the cosmic distance scale. [ABSTRACT FROM AUTHOR]

Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims. This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods. Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results. We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 103 M⊙) clusters. They are highly obscured (AV ∼ 5-24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ∼30-50 M⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the nature of 48 low-level stellar overdensities (from Froebrich, Scholz and Raftery catalogue - FSR07) projected towards the Galactic anticentre and derive fundamental parameters for the confirmed clusters, thus improving the open cluster (OC) census in that direction. Parameters are derived with field-star decontaminated photometry, colour-magnitude filters and stellar radial density profiles. Among the 48 targets, we identified 18 star clusters, six previously studied OCs and seven probable clusters that require deeper photometry to establish the nature. We discovered seven new clusters, six of them forming an association of clusters with BPI 14, FSR 777, Kronberger 1 and Stock 8 in the region of the nebula IC 417 and related to the Aur OB2 association, and one embedded in the nebula Sh2-229. We also derive parameters for these three non-FSR07 clusters, because they are important in determining the structure of the Galactic anticentre. Thus, 58 objects are analysed in this work and we could derive fundamental parameters for 28 of them. The scenario in the IC 417 star-forming region is consistent with a sequential event. FSR 888 and FSR 890 are embedded in Sh2-249 within the Gem OB1 association. According to the distance derived for these clusters and those in the association of clusters, both Aur OB2 and Gem OB1 are located in the Perseus arm. [ABSTRACT FROM AUTHOR]

ABSTRACT It is currently widely accepted that open star clusters and stellar associations result from the evolution of embedded star clusters. Parameters such star formation efficiency, time-scale of gas removal and velocity dispersion can be determinants of their future as bound or unbound systems. Finding objects at an intermediate evolution state can provide constraints to model the embedded cluster evolution. In the H ii region IC 1396, Trumpler 37 is an extended young cluster that presents characteristics of an association. We employed the Two Micron All Sky Survey (2MASS) photometry for analysing its structure and stellar content, and determining its astrophysical parameters. We also analysed 11 bright-rimmed clouds in IC 1396 in order to search for young infrared star clusters, and the background open star cluster Teutsch 74, to verify whether it has any contribution to the observed stellar density profile of Trumpler 37. The derived parameters and comparison with template objects from other studies lead us to conclude that Trumpler 37, rather than as a star cluster, will probably emerge from its molecular cloud as an OB association. [ABSTRACT FROM AUTHOR]

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Teutsch 145 and Teutsch 146 are shown to be open clusters (OCs) orbiting well inside the solar circle, a region where several dynamical processes combine to disrupt most OCs on a time-scale of a few 108 yr. BVI photometry from the GALILEO telescope is used to investigate the nature and derive the fundamental and structural parameters of the optically faint and poorly known OCs Teutsch 145 and 146. These parameters are computed by means of field-star-decontaminated colour–magnitude diagrams and stellar radial density profiles (RDPs). Cluster mass estimates are made based on the intrinsic mass functions (MFs). We derive the ages and , and the distances from the Sun and , respectively, for Teutsch 145 and 146. Their integrated apparent and absolute magnitudes are and 13.3 and and −5.3. The MFs (detected for stars with ) have slopes similar to Salpeter's initial mass function. Extrapolated to the H-burning limit, the MFs would produce total stellar masses of , typical of relatively massive OCs. Both OCs are located deep into the inner Galaxy and close to the Crux–Scutum arm. Since cluster-disruption processes are important, their primordial masses must have been higher than the present-day values. The conspicuous stellar density excess observed in the innermost bin of both RDPs might reflect the dynamical effects induced by a few of external tidal stress. [ABSTRACT FROM AUTHOR]

The very young open cluster (OC) NGC 2244 in the Rosette Nebula was studied with field-star-decontaminated Two-Micron All-Sky Survey (2MASS) photometry, which shows the main-sequence (MS) stars and an abundant pre-MS (PMS) population. Fundamental and structural parameters were derived with colour–magnitude diagrams (CMDs), stellar radial density profiles (RDPs) and mass functions (MFs). Most previous studies centred NGC 2244 close to the bright K0V star 12 Monocerotis, which is not a cluster member. Instead, the near-infrared RDP indicates a pronounced core near the O5 star HD 46150. We derive an age within 1–6 Myr, an absorption , a distance from the Sun (≈1.5 kpc outside the solar circle), an MF slope and a total (MS+PMS) stellar mass of . Its RDP is characterized by the core and cluster radii and , respectively. Departure from dynamical equilibrium is suggested by the abnormally large core radius and the marked central stellar excess. We also investigate the elusive neighbouring OC NGC 2239, which is low mass , young rather absorbed , and located in the background of NGC 2244 at . Its RDP follows a King-like function of and . The MF slope, , is essentially Salpeter's initial mass function. NGC 2244 is probably doomed to dissolution in a few 107 yr. Wide-field extractions and field-star decontamination increase the stellar statistics and enhance both CMDs and RDPs, which is essential for faint and bright star clusters. [ABSTRACT FROM AUTHOR]

We employ the recently installed near-infrared Multi-Conjugate Adaptive Optics demonstrator (MAD) to determine the basic properties of a newly identified, old and distant, Galactic open cluster (FSR 1415). The MAD facility remarkably approaches the diffraction limit, reaching a resolution of 0.07 arcsec (in K), that is also uniform in a field of ∼1.8 arcmin in diameter. The MAD facility provides photometry that is 50 per cent complete at . This corresponds to about 2.5 mag below the cluster main-sequence turn-off. This high-quality data set allows us to derive an accurate heliocentric distance of 8.6 kpc, a metallicity close to solar and an age of ∼2.5 Gyr. On the other hand, the deepness of the data allows us to reconstruct (completeness-corrected) mass functions (MFs) indicating a relatively massive cluster, with a flat core MF. The Very Large Telescope/MAD capabilities will therefore provide fundamental data for identifying/analysing other faint and distant open clusters in the Galaxy III and IV quadrants. [ABSTRACT FROM AUTHOR]

Abstract: We derive fundamental parameters of the embedded cluster DBSB 48 in the southern nebula Hoffleit 18 and the very young open cluster Trumpler 14, by means of deep JHK s infrared photometry. We build colour–magnitude and colour–colour diagrams to derive reddening and age, based on main sequence and pre-main sequence distributions. Radial stellar density profiles are used to study cluster structure and guide photometric diagram extractions. Field-star decontamination is applied to uncover the intrinsic cluster sequences in the diagrams. Ages are inferred from K-excess fractions. A prominent pre-main sequence population is present in DBSB 48, and the K-excess fraction f K =55±6% gives an age of 1.1±0.5Myr. A mean reddening of was found, corresponding to A V =8.2±0.3. The cluster CMD is consistent with the far kinematic distance of 5kpc for Hoffleit 18. For Trumpler 14 we derived similar parameters as in previous studies in the optical, in particular an age of 1.7±0.7Myr. The fraction of stars with infrared excess in Trumpler 14 is f K =28±4%. Despite the young ages, both clusters are described by a King profile with core radii R core =0.46±0.05pc and R core =0.35±0.04pc, respectively, for DBSB 48 and Trumpler 14. Such cores are smaller than those of typical open clusters. Small cores are probably related to the cluster formation and/or parent molecular cloud fragmentation. In DBSB 48, the magnitude extent of the upper main sequence is ΔK s ≈2mag, while in Trumpler 14 it is ΔK s ≈5mag, consistent with the estimated ages. [Copyright &y& Elsevier]

We report the discovery of a new open cluster (OC) in the Galaxy at and . Its field includes the planetary nebula (PN) PK 167−0.1. We study the possible associations of the PN/OC pairs NGC 2818/2818A, NGC 2438/M 46 (NGC 2437), PK 6+2.5/NGC 6469, as well as of the PN PK 167−0.1 with New Cluster 1. The analyses are based on near-infrared colour–magnitude diagrams (CMDs) and stellar radial density profiles. NGC 6469 is located in a heavily contaminated bulge field. The CMD morphology, especially for the latter two cases, is defined with a field-star decontamination algorithm applied to the 2MASS J, H and Ks photometry. Field decontamination for the OCs NGC 2818A and M 46 produced better defined CMDs and more accurate cluster parameters than in the literature. Those pieces of evidence point to M 46 as physically associated with the PN NGC 2438. The same occurs for the OC NGC 2818A and the PN NGC 2818; however, previous radial velocity arguments indicate that they are not associated. The OC NGC 6469 does not appear to be associated with the PN PK 6+2.5, which probably belongs to the bulge. Finally, the distance of the OC New Cluster 1 is consistent with a physical association with the PN PK 167−0.1. [ABSTRACT FROM AUTHOR]

Star clusters projected on to dense stellar fields in general require field-star (FS) decontamination to confirm their nature and derive intrinsic photometric and structural fundamental parameters. This work focuses on the open clusters (OCs) or candidates NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37 which are projected within and , against crowded bulge and/or disc fields. To tackle these difficult objects we develop a colour–magnitude diagram FS-decontamination algorithm based on 2MASS J, ( J− H) and data, and respective uncertainties, to detect cluster star excesses over the background. On the other hand, colour–magnitude filters are used to build stellar radial density profiles and mass functions. The results convey compelling evidence that Lyngå 9 and Czernik 37 are intermediate-age OCs, and their fundamental parameters are measured for the first time. Trumpler 23 is a particularly challenging object, since besides high background level, its field presents variable absorption in near-infrared bands. We confirm it to be an intermediate-age OC. Trumpler 26 is studied in more detail than in previous works, while NGC 5715 and Lyngå 4 have fundamental parameters determined for the first time. These OCs are located 0.9–1.6 kpc within the solar circle, with ages similar to that of the Hyades. Structurally, they are well described by King profiles. In all cases, core and limiting radii are significantly smaller than those of nearby OCs outside the solar circle. We test the effect of background levels on cluster radii determinations by means of simulations. They indicate that for central clusters, radii may be underestimated by about 10–20 per cent, which suggests that the small sizes measured for the present sample reflect as well intrinsic properties related to dynamical evolution effects. The objects probably have been suffering important tidal effects that may have accelerated dynamical evolution, especially in Czernik 37, the innermost object. [ABSTRACT FROM AUTHOR]

This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the J -, H - and K s - bands obtained from the Vista Variables in the Vía Láctea (VVV) Survey. We performed in each cluster field a variability search using Stetson’s variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study, 157 in total in three different known OCs, are classified based on their light curve shapes, periods, amplitudes and their location in the corresponding color-magnitude ( J − K s , K s ) and color-color ( H − K s , J − H ) diagrams. We found 5 possible Cepheid stars which, based on the period-luminosity relation, are very likely type II Cepheids located behind the bulge. Among the newly discovered variables, there are eclipsing binaries, δ Scuti, as well as background RR Lyrae stars. Using the new version of the Wilson & Devinney code as well as the “Physics Of Eclipsing Binaries” (PHOEBE) code, we analyzed some of the best eclipsing binaries we discovered. Our results show that these studied systems turn out to be ranging from detached to double-contact binaries, with low eccentricities and high inclinations of approximately 80°. Their surface temperatures range between 3500 K and 8000 K. [ABSTRACT FROM AUTHOR]