A. Moitinho

New catalogue of optically visible open clusters and candidates

We have compiled a new catalogue of open clusters in the Galaxy which updates the previous cat- alogues of Lyng a (1987) and of Mermilliod (1995) (included in the WEBDA database). New objects and new data, in particular, data on kinematics (proper motions) that were not present in the old catalogues, have been included. Virtually all the clusters (1537) presently known were included, which represents an increment of about 347 objects relative to the Lyng a (1987) catalogue. The catalogue is presented in a single table con- taining all the important data, which makes it easy to use. The catalogue can be accessed on line either at http://www.astro.iag.usp.br/~wilton/ or as an electronic table which will be made available at the CDS.

Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate

ABSTRACT With the discovery of the Sagittarius dwarf spheroidal (Ibata et al. 1994), a galaxycaught in the process of merging with the Milky Way, the hunt for other such ac-cretion events has become a very active field of astrophysical research. The identifi-cation of a stellar ring-like structure in Monoceros, spanning more than 100 degrees(Newberg et al. 2002), and the detection of an overdensity of stars in the directionof the constellation of Canis Major (CMa; Martin et al. 2004), apparently associatedto the ring, has led to the widespread belief that a second galaxy being cannibalisedby the Milky Way had been found. In this scenario, the overdensity would be theremaining core of the disrupted galaxy and the ring would be the tidal debris leftbehind. However, unlike the Sagittarius dwarf, which is well below the Galactic planeand whose orbit, and thus tidal tail, is nearly perpendicular to the plane of the MilkyWay, the putative CMa galaxy and ring are nearly co-planar with the Galactic disk.This severely complicates the interpretation of observations. In this letter, we showthat our new description of the Milky Way leads to a completely different picture. Weargue that the Norma-Cygnus spiral arm defines a distant stellar ring crossing Mono-ceros and the overdensity is simply a projection effect of looking along the nearbylocal arm. Our perspective sheds new light on a very poorly known region, the thirdGalactic quadrant (3GQ), where CMa is located.Key words: Galaxy: structure — open clusters and associations: general — Galaxy:stellar content — galaxies: dwarf

SPIRAL STRUCTURE IN THE OUTER GALACTIC DISK. I. THE THIRD GALACTIC QUADRANT

We combine optical and radio observations to trace the spiral structure in the third quadrant of the Milky Way. The optical observations consist of a large sample of young open clusters and associations, whereas the radio observations consist of a surveyofnearbyand distant clouds observedinCO. Boththe optical and radio samples are the largest ones thus far presented in the literature. We use this unique material to analyze the behavior of interstellar extinction and totracethedetailedstructureofthethirdGalacticquadrant(TGQ).Wefindthattheouter(Cygnus)granddesignspiral arm is traced by stellar and CO components, while the Perseus arm is traced solely by CO and is possibly being disrupted by the crossing of the Local (Orion) arm. The Local arm is traced by CO and young stars toward l ¼ 240 � and extends for over 8 kpc along the line of sight reaching the outer arm. Finally, we characterize the Galactic warp and compare the geometries implied by the young stellar and CO components.

Gaia Data Release 1 - Catalogue validation

Before the publication of the Gaia Catalogue, the contents of the first data release have undergone multiple dedicated validation tests. These tests aim at analysing in-depth the Catalogue content to detect anomalies, individual problems in specific objects or in overall statistical properties, either to filter them before the public release, or to describe the different caveats of the release for an optimal exploitation of the data. Dedicated methods using either Gaia internal data, external catalogues or models have been developed for the validation processes. They are testing normal stars as well as various populations like open or globular clusters, double stars, variable stars, quasars. Properties of coverage, accuracy and precision of the data are provided by the numerous tests presented here and jointly analysed to assess the data release content. This independent validation confirms the quality of the published data, Gaia DR1 being the most precise all-sky astrometric and photometric catalogue to-date. However, several limitations in terms of completeness, astrometric and photometric quality are identified and described. Figures describing the relevant properties of the release are shown and the testing activities carried out validating the user interfaces are also described. A particular emphasis is made on the statistical use of the data in scientific exploitation.

ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations

ESPRESSO, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, will combine the efficiency of modern echelle spectrograph design with extreme radial-velocity precision. It will be installed on ESOs VLT in order to achieve a gain of two magnitudes with respect to its predecessor HARPS, and the instrumental radialvelocity precision will be improved to reach cm/s level. Thanks to its characteristics and the ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in various fields of astronomy. The main scientific objectives will be the search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M-dwarfs, and the analysis of the variability of fundamental physical constants. We will present the ambitious scientific objectives, the capabilities of ESPRESSO, and the technical solutions of this challenging project.

Detection of a young stellar population in the background of open clusters in the third galactic quadrant

We report the detection of a young stellar population (≤100 Myr) in the background of nine young open clusters belonging to a homogenous sample of 30 star clusters in the third Galactic quadrant (at 217° ≤ l ≤ 260°). Deep and accurate UBVRI photometry allows us to measure model-independent age and distance for the clusters and the background population with high confidence. This population is exactly the same population (the blue plume) recently detected in three intermediate-age open clusters and suggested to be a ≤1-2 Gyr old population belonging to the Canis Major (CMa) overdensity (Bellazzini et al.; Martinez-Delgado et al.). However, we find that the young population in those three clusters and in six clusters of our sample follows the pattern of the Norma-Cygnus spiral arm as defined by CO clouds remarkably well, while in the other three program clusters it lies in the Perseus arm. We finally provide one example (out of 21) of a cluster that does not show any background population, demonstrating that this population is not ubiquitous toward CMa.

NGC 2362: A Template for Early Stellar Evolution*

We present UBVRI photometry for the young open cluster NGC 2362. From analysis of the appropriate color-color and color-magnitude diagrams we derive the fundamental parameters of the NGC 2362 cluster to be age = 5 Myr, distance = 1480 pc, and E(B-V) = 0.10 mag. The cluster age was independently determined for both high-mass (2.1-36 M☉) and low-mass (0.7-1.2 M☉) stars with excellent agreement between the ages derived using post-main-sequence (Girardi et al. 2000) and pre-main-sequence (Baraffe et al. 1998) evolutionary tracks for the high- and low-mass stars, respectively. Analysis of this clusters color-magnitude diagram reveals a well-defined pre-main sequence (covering ΔV ~ 9 mag in V and extending from early A stars to near the hydrogen-burning limit), which makes this cluster an ideal laboratory for pre-main-sequence evolution studies.

On the difference between nuclear and contraction ages

Context. Ages derived from low mass stars still contracting onto the main sequence often differ from ages derived from the high mass ones that have already evolved away from it. Aims. We investigate the general claim of disagreement between these two independent age determinations by presenting UBVRI photometry for the young galactic open clusters NGC 2232, NGC 2516, NGC 2547 and NGC 4755, spanning the age range ∼10–150 Myr Methods. We derived reddenings, distances, and nuclear ages by fitting ZAMS and isochrones to color–magnitudes and color–color diagrams. To derive contraction ages, we used four different pre-main sequence models, with an empirically calibrated color-temperature relation to match the Pleiades cluster sequence. Results. When exclusively using the V vs. V −I color–magnitude diagram and empirically calibrated isochrones, there is consistency between nuclear and contraction ages for the studied clusters. Although the contraction ages seem systematically underestimated, in none of the cases do they deviate by more than one standard deviation from the nuclear ages.

Gaia Data Release 2: Catalogue validation

Context. The second Gaia data release (DR2) contains very precise astrometric and photometric properties for more than one billion sources, astrophysical parameters for dozens of millions, radial velocities for millions, variability information for half a million stars from selected variability classes, and orbits for thousands of solar system objects. Aims: Before the catalogue was published, these data have undergone dedicated validation processes. The goal of this paper is to describe the validation results in terms of completeness, accuracy, and precision of the various Gaia DR2 data. Methods: The validation processes include a systematic analysis of the catalogue content to detect anomalies, either individual errors or statistical properties, using statistical analysis and comparisons to external data or to models. Results: Although the astrometric, photometric, and spectroscopic data are of unprecedented quality and quantity, it is shown that the data cannot be used without dedicated attention to the limitations described here, in the catalogue documentation and in accompanying papers. We place special emphasis on the caveats for the statistical use of the data in scientific exploitation. In particular, we discuss the quality filters and the consideration of the properties, systematics, and uncertainties from astrometry to astrophysical parameters, together with the various selection functions.

Open clusters in the third galactic quadrant - I. Photometry

We have performed a photometric survey of open clusters in the third Galactic quadrant in order to study the star formation history and spatial structure in the Canis Major-Puppis-Vela region. In this paper we describe a catalogue of CCD