Eduardo Luiz Damiani Bica

VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way

Original article can be found at: http://www.sciencedirect.com/science/journal/13841076 Copyright Elsevier B.V.

Age and metallicity distribution of the Galactic bulge from extensive optical and near-IR stellar photometry

We present a new determination of the metallicity distribution, age, and luminosity function of the Galactic bulge stellar population. By combining near-IR data from the 2MASS survey, from the SOFI imager at ESO NTT and the NICMOS camera on board HST we were able to construct color-magnitude diagrams (CMD) and luminosity functions (LF) with large statistics and small photometric errors from the Asymptotic Giant Branch (AGB) and Red Giant Branch (RGB) tip down to ∼0.15 M� . This is the most extended and complete LF so far obtained for the galactic bulge. Similar near-IR data for a disk control field were used to decontaminate the bulge CMDs from foreground disk stars, and hence to set a stronger constraint on the bulge age, which we found to be as large as that of Galactic globular clusters, or >10 Gyr. No trace is found for any younger stellar population. Synthetic CMDs have been constructed to simulate the effect of photometric errors, blending, differential reddening, metallicity dispersion and depth effect in the comparison with the observational data. By combining the near-IR data with optical ones, from the Wide Field Imager at the ESO/MPG 2.2 m telescope, a disk-decontaminated (MK,V-K )C MD has been constructed and used to derive the bulge metallicity distribution, by comparison with empirical RGB templates. The bulge metallicity is found to peak at near solar value, with a sharp cutoff just above solar, and a tail towards lower metallicity that does not appreciably extend below (M/H) ∼− 1.5.

Theoretical isochrones compared to 2MASS observations: Open clusters at nearly solar metallicity

We study classical disk clusters at nearly solar metallicity with ages in the range 200 Myr - 6 Gyr using 2MASS pho- tometry and theoretical isochrones. As a first step we employ J, H and K Johnsons Padova isochrones which, on a large scale, result in a good fit of the observed data. However, we find some significant deviations, especially in the red giant branch for intermediate age clusters and the low-mass main-sequence end in general. Subsequently, isochrones involving the 2MASS J, H and KS transmission curves were generated which account for differences of ≈0.02 of the above deviations, in the sense re- quired by the 2MASS observations. However, these corrections are not enough to fully account for the observed differences. We suggest that the remaining deviations should be accounted for by model atmosphere limitations, particularly the lack of molec- ular opacity data in low-temperature giants. Future models will incorporate these updated data in order to produce isochrones suitable for the whole range of stellar masses.

New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS

We carried out a survey of infrared star clusters and stellar groups on the 2MASS J, H and Ks all-sky release Atlas in the Northern and Equatorial Milky Way (350 ◦ <�< 360 ◦ ,0 ◦ <�< 230 ◦ ). The search in this zone complements that in the Southern Milky Way (Dutra et al. 2003a). The method concentrates efforts on the directions of known optical and radio nebulae. The present study provides 167 new infrared clusters, stellar groups and candidates. Combining the two studies for the whole Milky Way, 346 infrared clusters, stellar groups and candidates were discovered, whereas 315 objects were previously known. They constitute an important new sample for future detailed studies.

Low-extinction windows in the inner Galactic Bulge

We built K band extinction maps in the area of two candidate low-extinction windows in the inner Bulge: W0.2-2.1 at (l,b) = (0.25o,-2.15o), and W359.4-3.1 at (l,b) = (359.40o,-3.10o). We employed JHKs photometry from the 2MASS Point Source Catalog. Extinction values were determined by fitting the upper giant branch found in the present 2MASS Ks x J-Ks diagrams to a de-reddened bulge stellar population reference giant branch. We tested the method on the well known Baades and Sgr I windows: the 2MASS mean extinction values in these fields agreed well with those of previous studies. We confirm the existence of low-extinction windows in the regions studied, as local minima in the A_K maps reaching A_K values about 2 standard deviations below the mean values found in the neighbouring areas. Schlegel et al.s (1998) FIR extinction maps, which integrate dust contributions throughout the Galaxy, are structurally similar to those derived with 2MASS photometry in the two studied windows. We thus conclude that the dust clouds affecting the 2MASS and FIR maps in these directions are basically the same and are located on foreground of the bulk of bulge stars. However, the A_K absolute values differ significantly. In particular, the FIR extinction values for W359.4-3.1 are a factor ~1.45 larger than those derived from the 2MASS photometry. Possible explanations of this effect are discussed. The lower Galactic latitudes of the low-extinction windows W359.4-3.1 and W0.2-2.1, as compared to Baades Window, make them promising targets for detailed studies of more central bulge regions.

Globular cluster system and Milky Way properties revisited

Aims. Updated data of the 153 Galactic globular clusters are used to readdress fundamental parameters of the Milky Way, such as the distance of the Sun to the Galactic centre, the bulge and halo structural parameters, and cluster destruction rates. Methods. We build a reduced sample that has been decontaminated of all the clusters younger than 10 Gyr and of those with retrograde orbits and/or evidence of relation to dwarf galaxies. The reduced sample contains 116 globular clusters that are tested for whether they were formed in the primordial collapse. Results. The 33 metal-rich globular clusters ([Fe/H] ≥− 0.75) of the reduced sample basically extend to the Solar circle and are distributed over a region with the projected axial-ratios typical of an oblate spheroidal, ∆x : ∆y : ∆z ≈ 1. 0:0 . 9:0 .4. Those outside this region appear to be related to accretion. The 81 metal-poor globular clusters span a nearly spherical region of axial-ratios ≈1. 0:1 . 0:0 .8 extending from the central parts to the outer halo, although several clusters in the external region still require detailed studies to unravel their origin as accretion or collapse. A new estimate of the Sun’s distance to the Galactic centre, based on the symmetries of the spatial distribution of 116 globular clusters, is provided with a considerably smaller uncertainty than in previous determinations using globular clusters, RO = 7.2 ± 0.3 kpc. The metal-rich and metal-poor radial-density distributions flatten for RGC ≤ 2 kpc and are represented well over the full Galactocentric distance range both by a power-law with a core-like term and Sersic’s law; at large distances they fall off as ∼R −3.9 . Conclusions. Both metallicity components appear to have a common origin that is different from that of the dark matter halo. Structural similarities between the metal-rich and metal-poor radial distributions and the stellar halo are consistent with a scenario where part of the reduced sample was formed in the primordial collapse and part was accreted in an early period of merging. This applies to the bulge as well, suggesting an early merger affecting the central parts of the Galaxy. The present decontamination procedure is not sensitive to all accretions (especially prograde) during the first Gyr, since the observed radial density profiles still preserve traces of the earliest merger(s). We estimate that the present globular cluster population corresponds to ≤23 ± 6% of the original one. The fact that the volume-density radial distributions of the metal-rich and metal-poor globular clusters of the reduced sample follow both a core-like power-law, and Sersic’s law indicates that we are dealing with spheroidal subsystems at all scales.

A search for old star clusters in the large magellanic cloud

We report the first results of a color-magnitude diagram survey of 25 candidate old LMC clusters. For almost all of the sample, it was possible to reach the turnoff region, and in many clusters we have several magnitudes of the main sequence. Age estimates based on the magnitude difference

A Revised and Extended Catalog of Magellanic System Clusters, Associations, and Emission Nebulae. II. The Large Magellanic Cloud

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A general catalogue of extended objects in the Magellanic System

between the giant branch clump and the turnoff revealed that no new old clusters were found. The candidates turned out to be of intermediate age (1-3 Gyr) We show that the apparently old ages as inferred from integrated UBV colors can be explained by a combination of stochastic effects produced by bright stars and by photometric errors for faint clusters lying in crowded fields. The relatively metal poor candidates from the CaII triplet spectroscopy also turned out to be of intermediate age. This, combined with the fact that they lie far out in the disk, yields interesting constraints regarding the formation and evolution of the LMC disk. We also study the age distribution of intermediate age and old clusters This homogeneous set of accurate relative ages allows us to make an improved study of the history of cluster formation/destruction for ages

Open clusters in dense fields: the importance of field-star decontamination for NGC 5715, Lyngå 4, Lyngå 9, Trumpler 23, Trumpler 26 and Czernik 37

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