Stellar evolution models predict that internal mixing should cause some sodium overabundance at the surface of red giants more massive than ~1.5-2.0M_{aun}_. The surface aluminium abundance should not be affected. Nevertheless, observational results disagree about the presence and/or the degree of Na and Al overabundances. In addition, Galactic chemical evolution models adopting different stellar yields lead to very different predictions for the behavior of [Na/Fe] and [Al/Fe] versus [Fe/H]. Overall, the observed trends of these abundances with metallicity are not well reproduced. We re-address both issues, using new Na and Al abundances determined within the Gaia-ESO Survey. Our aim is to obtain better observational constraints on the behavior of these elements using two samples: i) more than 600 dwarfs of the solar neighborhood and of open clusters and ii) low- and intermediate-mass clump giants in six open clusters. Abundances were determined using high-resolution UVES spectra. The individual Na abundances were corrected for nonlocal thermodynamic equilibrium effects. For the Al abundances, the order of magnitude of the corrections was estimated for a few representative cases. For giants, the abundance trends with stellar mass are compared to stellar evolution models. For dwarfs, the abundance trends with metallicity and age are compared to detailed chemical evolution models.
The table presents tidal parameters and masses of 236 open clusters in the nearest kiloparsecs around the Sun. The parameters are derived from a fitting of three-parameter King profiles to the the observed density distribution. The clusters are sub-sample of the Catalogue of Open Cluster Data and their members are selected from high precision homogeneous all sky catalogue ASCC-2.5 (Kharchenko, 2001, Cat. <I/280>). Up to four cluster membership samples in wide cluster area are considered for every cluster and the best solution is presented in the table. Clusters in the table are sorted by numbers in the COCD order.
We have determined stellar membership based on astrometry, primarily from TGAS and HSOY, and multi-band photometry for 24 clusters within 333 pc. The fundamental cluster parameters (distance, age, and reddening) have been derived by fitting Padova isochrones (Bressan et al. 2012) to the cluster photometry using a chi-squared minimization.
In a previous paper we obtained King's parameters for 236 of 650 Galactic open clusters identified in the ASCC-2.5 (Kharchenko, 2001, Cat. <I/280>). Our aims is the estimate tidal radii by use of observable parameters available for all clusters. Bias-free results are required. We use methods of stellar statistics and develop a semi-empirical model of open clusters.
We have carried out near-infrared (NIR) imaging observations of the Carina Nebula for an area of ~400arcmin^29 including the clusters Trumpler 14 and Trumpler 16, with 10sigma limits of J~18.5, H~17.5, and Ks ~16.5mag. A total of 544 Class II candidates, 11 Class I candidates, and 40 red (H-Ks>2) sources have been found.
We have conducted aperture polarimetry of ~500 stars of the Orion Nebula Cluster in M42 based on our wide-field (~8'x8') JHKs-band polarimetry. Most of the near-infrared (NIR) polarizations are dichroic, with position angles of polarization agreeing, both globally and locally, with previous far-infrared (FIR) and submillimeter observations, having taken into account the 90{deg} difference in angles between dichroic absorption and emission. This is consistent with the idea that both NIR dichroic polarizations and FIR/submillimeter thermal polarizations trace the magnetic fields in the OMC-1 region.
We want to study the content of young stellar objects in the RCW 38 cluster by means of multi-epoch variability studies. We performed a three-month near-infrared (NIR) monitoring campaign of the young cluster RCW 38 using the 80cm IRIS telescope near Cerro Armazones, Chile. Variability data with a median sampling of 1 day was gathered for 1026 sources, while a total of 3433 sources in JHK could be studied in the co-added, deep images with a completeness limit of K<15mag.
We present near-IR (NIR) J, H and K mosaic images of the active star forming region associated with the optical reflection nebula NGC 1333. These observations cover an area of 10'x10' and are centered on the energetic outflow source SSV 13. From these data, we have obtained NIR photometry of 134 objects down to a 5{sigma} limiting K magnitude of mK=16.2 and a conservative survey completeness limit of mK=16.0. With the addition of new optical R and I band CCD photometry, and both (sub)mm line and continuum maps, we analyse and discuss the region's morphology and spatial source distribution with additional reference to existing multi-wavelength data.
Young massive clusters are key to map the Milky Way's structure, and near-IR large area sky surveys have contributed strongly to the discovery of new obscured massive stellar clusters. We present the third article in a series of papers focused on young and massive clusters discovered in the VVV survey. This article is dedicated to the physical characterization of VVV CL086, using part of its OB-stellar population. We physically characterized the cluster using JHKs near-infrared photometry from ESO public survey VVV images, using the VVV-SkZ pipeline, and near-infrared K-band spectroscopy, following the methodology presented in the first article of the series. Individual distances for two observed stars indicate that the cluster is located at the far edge of the Galactic bar. These stars, which are probable cluster members from the statistically field-star decontaminated CMD, have spectral types between O9 and B0V. According to our analysis, this young cluster (1.0Myr<age<5.0Myr) is located at a distance of 11kpc, and we estimate a lower limit for the cluster total mass of 2800 solar masses. It is likely that the cluster contains even earlier and more massive stars.
Studying stellar pulsations in open clusters offers the possibility of performing ensemble asteroseismology. The reasonable assumption that the cluster members have the same age, distance, and overall metallicity aids in the seismic modelling process and tightly constrains it. Therefore it is important to identify open clusters with many pulsators. New pulsating stars of the beta Cephei type were searched for among the members of the open cluster NGC 637. Thirty-one hours of time-resolved V filter CCD photometry were obtained. The measurements confirmed two previously known variables, and revealed three new beta Cephei stars and one more candidate. All four pulsators have sufficiently large amplitudes for easy mode identification and are multiperiodic. With four certain pulsating members, NGC 637 is now among the open clusters that are richest in beta Cephei stars. It is thus an excellent target for ensemble asteroseismology, and to examine the differences between pulsating and apparently constant stars in the beta Cephei domain.