New photometric material is presented for six outer disc supposedly old, Galactic star clusters: Berkeley 76, Haffner 4, Ruprecht 10, Haffner 7, Haffner 11 and Haffner 15, which are projected against the rich and complex Canis Major overdensity at 225 degrees <= l <= 248 degrees, -7 degrees <= b <= -2 degrees. This CCD data set, in the UBVI passbands, is used to derive their fundamental parameters, in particular age and distance. Four of the program clusters turn out to be older than 1 Gyr. This fact makes them ideal targets for future spectroscopic campaigns aiming at deriving their metal abundances. This, in turn, contributes to increase the number of well-studied outer disc old open clusters. Only Haffner 15, previously considered an old cluster, is found to be a young, significantly reddened cluster, member of the Perseus arm in the third Galactic quadrant. As for Haffner 4, we suggest an age of about half a Gyr. The most interesting result we found is that Berkeley 76 is probably located at more than 17 kpc from the Galactic centre, and therefore is among the most peripherical old open clusters so far detected. Besides, for Ruprecht 10 and Haffner 7, which were never studied before, we propose ages larger than 1 Gyr.

Context. The existence of lithium-rich low-mass red giant stars still represents a challenge for stellar evolution models. Stellar clusters are privileged environments for this kind of investigation.

Context. The discovery of brown dwarfs (BDs) in the solar neighborhood and young star clusters has helped to constraint the low-mass end of the stellar mass function and the initial mass function. We use data of the Vista Variables in the Via Lactea (VVV), a near-infrared (NIR) multi-wavelength (ZYJH K-s) multi-epoch (K-s) ESO Public Survey mapping the Milky Way bulge and southern Galactic plane to search for nearby BDs.

We present medium-resolution optical (lambda/Delta lambda similar to 4000) and near-infrared (lambda/Delta lambda similar to 8000) spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 angstrom Li i absorption in both Luhman 16A (8.0 +/- 0.4 angstrom) and Luhman 16B (3.8 +/- 0.4 angstrom) confirming their substellar mass. Interestingly, this is the first detection of Li i absorption in a T dwarf. In the near-infrared data, we find strong K I absorption at 1.168, 1.177, 1.243, and 1.254 mu m in both components. Neither the optical nor the near-infrared alkali lines show low surface gravity signatures. Along with the Li i absorption detection, we can broadly constrain the system age to 0.1-3 Gyr or the mass to 20-65M(Jup) for each component. Compared to the strength of K I line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J-band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 mu m and 1.25 m regions than Luhman 16A. Converting flux units to a brightness temperature we interpret this to mean that the secondary is similar to 50 K warmer than the primary in regions dominated by condensate grain scattering. One plausible explanation for this difference is that Luhman 16B has thinner clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter regions. We also detect comparably strong FeH in the 0.9896 mu m Wing-Ford band for both components. Traditionally, a signpost of changing atmosphere conditions from late-type L to early T, the persistence and similarity of FeH at 0.9896 mu m in both Luhman 16A and Luhman 16B is an indication of homogenous atmosphere conditions. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within 1 sigma with resultant T-effs of 1310 +/- 30 K and 1280 +/- 75 K for Luhman 16AB respectively.

New and existing X-ray, UBVJHK(s)W((1-4)), and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance because they host the classical Cepheids USgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids' period evolution (dP/dt) from similar to 140 years of observations, helped to resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, the distances derived for members of M25 and NGC7790 are 630 +/- 25 pc and 3.40 +/- 0.15 kpc, respectively.

Using FORS2 on the Very Large Telescope, we have astrometrically monitored over a period of two months the two components of the brown dwarf system WISE J104915.57-531906.1, the closest one to the Sun. Our astrometric measurements - with a relative precision at the milli-arcsecond scale - allowed us to detect the orbital motion and derive more precisely the parallax of the system, leading to a distance of 2.020 +/- 0.019 pc. The relative orbital motion of the two objects is found to be perturbed, which leads us to suspect the presence of a substellar companion around one of the two components. We also performed VRIz photometry of the two components and compared this with models. We confirm the flux reversal of the T dwarf.

We present a new Y dwarf, WISE J030449.03-270508.3, confirmed from a candidate sample designed to pick out low-temperature objects from the Wide-field Infrared Survey Explorer (WISE) data base. The new object is typed Y0pec following a visual comparison with spectral standards, and lies at a likely distance of 10-17 pc. Its tangential velocity suggests thin disc membership, but it shows some spectral characteristics that suggest that it may be metal poor and/or older than previously identified Y0 dwarfs. Based on trends seen for warmer late-type T dwarfs, the Y-band flux peak morphology is indicative of sub-solar metallicity, and the enhanced red wing of the J-band flux peak offers evidence for high gravity and/or low metallicity (with associated model trends suggesting an age closer to similar to 10 Gyr and mass in the range 0.02-0.03 M-circle dot). This object may thus be extending the population parameter space of the known Y0 dwarfs.

Recent ground-based near-IR (NIR) studies of stellar clusters in nearby galaxies have suggested that young clusters remain embedded for 7-10 Myr in their progenitor molecular cloud, in conflict with optical-based studies which find that clusters are exposed after 1-3 Myr. Here, we investigate the role that spatial resolution plays in this apparent conflict. We use a recent catalogue of young (< 10 Myr) massive (> 5000M(circle dot)) clusters in the nearby spiral galaxy, M83, along with Hubble Space Telescope (HST) imaging in the optical and NIR, and ground-based NIR imaging, to see how the colours (and hence estimated properties such as age and extinction) are affected by the aperture size employed, in order to simulate studies of differing resolution. We find that the NIR is heavily affected by the resolution, and when aperture sizes > 40 pc are used, all young/blue clusters move redwards in colour space, which results in their appearance as heavily extincted clusters. However, this is due to contamination from nearby sources and nebular emission, and is not an extinction effect. Optical colours are much less affected by resolution. Due to the larger effect of contamination in the NIR, we find that, in some cases, clusters will appear to show NIR excess when large (> 20 pc) apertures are used. Our results explain why few young (< 6 Myr), low-extinction (AV < 1 mag) clusters have been found in recent ground-based NIR studies of cluster populations, while many such clusters have been found in higher resolution HST-based studies. Additionally, resolution effects appear to (at least partially) explain the origin of the NIR excess that has been found in a number of extragalactic young massive clusters.

Context. The abundances of a-elements are a powerful diagnostic of the star formation history and chemical evolution of a galaxy. Sulphur. being moderately volatile, can be reliably measured in the interstellar medium (ISM) of damped Ly-alpha galaxies and extragalactic H-II regions. Measurements in stars of different metallicity in our Galaxy can then be readily compared to the abundances in external galaxies. Such a comparison is not possible for Si or Ca that suffer depletion onto dust in the ISM. Furthermore, studying sulphur is interesting because it probes nucleosynthetic conditions that are very different from those of Oar Mg. In this context measurements in star clusters are a reliable tracers of the Galactic evolution of sulphur.

Passing stars can perturb the Oort Cloud, triggering comet showers and potentially extinction events on Earth. We combine velocity measurements for the recently discovered, nearby, low- mass binary system WISE J072003.20084651.2 (" Scholz's star") to calculate its past trajectory. Integrating the Galactic orbits of this 0.15 Me binary system and the Sun, we find that the binary passed within only 52+ 23 - 14 kAU ( 0.25+ 0.11 - 0.07 pc) of the Sun 70+ 15 - 10 kya ( 1s uncertainties), i. e., within the outer Oort Cloud. This is the closest known encounter of a star to our solar system with a well- constrained distance and velocity. Previous work suggests that flybys within 0.25 pc occur infrequently ( 0.1 Myr- 1). We show that given the low mass and high velocity of the binary system, the encounter was dynamically weak. Using the best available astrometry, our simulations suggest that the probability that the star penetrated the outer Oort Cloud is 98%, but the probability of penetrating the dynamically active inner Oort Cloud (< 20 kAU) is 10- 4. While the flyby of this system likely caused negligible impact on the flux of longperiod comets, the recent discovery of this binary highlights that dynamically important Oort Cloud perturbers may be lurking among nearby stars.