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The detailed spiral structure in the outer Galactic disk is still poorly known, and for several Galactic directions we rely on model extrapolations. One of these regions is the fourth Galactic quadrant, in the sector comprised between Vela and Carina (270

We present new abundances and radial velocities for stars in the field of the open cluster Tombaugh 2, which has been suggested to be associated with the Galactic Anticenter Stellar Structure (also known as the Monoceros stream). Using VLT/FLAMES with the UVES and GIRAFFE spectrographs, we find a radial velocity (RV) of = 121 \pm 0.4 km/s using eighteen Tombaugh 2 cluster stars. Our abundance analysis of RV-selected members finds that Tombaugh 2 is more metal-rich than previous studies have found; moreover, unlike the previous work, our larger sample also reveals that stars with the velocity of the cluster show a relatively large spread in chemical properties (e.g., Delta[Fe/H] > 0.2). This is the first time a possible abundance spread has been observed in an open cluster, though this is one of several possible explanations for our observations. While there is an apparent trend of [alpha/Fe] with [Fe/H], the distribution of abundances of these "RV cluster members" also may hint at a possible division into two primary groups with different mean chemical characteristics -- namely (<[Fe/H]>,<[Ti/Fe]>) ~ (-0.06, +0.02) and (-0.28, +0.36). Based on position and kinematics Tombaugh 2 is a likely member of the GASS/Monoceros stream, which makes Tombaugh 2 the second star cluster within the originally proposed GASS/Monoceros family. However, we explore other possible explanations for the observed spread in abundances and two possible sub-populations, with the most likely explanation being that the metal-poor ([Fe/H] = -0.28), more centrally-concentrated population being the true Tombaugh 2 clusters stars and the metal-rich ([Fe/H] = -0.06) population being an overlapping, and kinematically associated, but "cold" (sigma_V < 2 km/s) stellar stream at R_{gc} >= 15 kpc., Comment: 15 pages, 7 figure, MNRAS in press

We present observations for three star clusters, Kron 11, Kron 63 and NGC 121, in the Small Magellanic Cloud. We have studied their structure and derived their fundamental parameters by means of their luminosity functions, their color magnitude diagrams and the Padova suite of isochrones. NGC 121 is a well studied object, for which we confirm previous evidence about its old age and low metal content, and have found that it is undergoing mass segregation. Kron 11 and Kron 63 are poorly populated clusters which had never been studied so far. Kron 11 is several gigayears younger than NGC 121, while Kron 63 is basically a very young star aggregate. Both clusters are immersed in dense stellar fields which share the same population properties, suggesting that in their cases, cluster ages are consistent with typical ages of field stars., Comment: 9 pages; 7 figures, MNRAS paper

We investigate the distribution of Blue Straggler stars in the field of three open star clusters. The main purpose is to highlight the crucial role played by general Galactic disk fore-/back-ground field stars, which are often located in the same region of the Color Magnitude Diagram as Blue Straggler stars. We analyze photometry taken from the literature of 3 open clusters of intermediate/old age rich in Blue Straggler stars, and which are projected in the direction of the Perseus arm, and study their spatial distribution and the Color Magnitude Diagram. As expected, we find that a large portion of the Blue Straggler population in these clusters are simply young field stars belonging to the spiral arm. This result has important consequences on the theories of the formation and statistics of Blue Straggler stars in different population environments: open clusters, globular clusters or dwarf galaxies. As previously emphasized by many authors, a detailed membership analysis is mandatory before comparing the Blue Straggler population in star clusters against theoretical models. Moreover, these sequences of young field stars (blue plumes) are potentially powerful tracers of Galactic structure which require further consideration., Comment: 11 pages, 4 figurs, in press as Research Note in A&A

We report on a new, wide field ($20^{\prime} \times 20^{\prime}$), multicolor ($UBVI$), photometric campaign in the area of the nearby old open cluster NGC 2112. At the same time, we provide medium-resolution spectroscopy of 35 (and high-resolution of additional 5) Red Giant and Turn Off stars. This material is analyzed with the aim to update the fundamental parameters of this traditionally difficult cluster, which is very sparse and suffers from heavy field star contamination. Among the 40 stars with spectra, we identified 21 {\it bona fide} radial velocity members which allow us to put more solid constraints on the cluster's metal abundance, long suggested to be as low as the metallicity of globulars. As indicated earlier by us on a purely photometric basis (Carraro et al. 2002), the cluster [Fe/H] abundance is slightly super-solar ([Fe/H] =0.16$\pm$0.03) and close to the Hyades value, as inferred from a detailed abundance analysis of 3 of the 5 stars with higher resolution spectra. Abundance ratios are also marginally super solar. Based on this result, we revise the properties of NGC 2112 using stellar models from the Padova and Yale-Yonsei groups. For this metal abundance, we find the cluster's age, reddening, and distance values are 1.8 Gyr, 0.60 mag, and 940 pc, respectively. Both the Yale-Yonsei and Padova models predict the same values for the fundamental parameters within the errors. Overall, NGC 2112 is a typical solar neighborhood, thin disk star cluster, sharing the same chemical properties of F-G stars and open clusters close to the Sun. This investigation outlines the importance of a detailed membership analysis in the study of disk star clusters., Comment: 12 pages, 10 eps figure, in press in MNRAS

We performed a photometric multicolor survey of the core of the Canis Major over-density at l 244, -8.0, reaching V = 22 and covering 0.3 x 1 degree. The main aim is to unravel the complex mixture of stellar populations toward this Galactic direction, where in the recent past important signatures of an accretion event have been claimed to be detected. While our previous investigations were based on disjointed pointings aimed at revealing the large scale structure of the third Galactic Quadrant, we now focus on a complete coverage of a smaller field centered on the Canis Major over-density. A large wave-length baseline, in the UBVRI bands, allows us to build up a suite of colour colour and colour magnitude diagrams, providing a much better diagnostic tool to disentangle the stellar populations of the region. In fact, the simple use of one colour magnitude diagram, widely employed in all the previous studies defending the existence of the Canis Major galaxy, does not allow one to separate the effects of the different parameters (reddening, age, metallicity, and distance) involved in the interpretation of data, forcing to rely on heavy modeling. In agreement with our previous studies in the same general region of the Milky Way, we recognize a young stellar population compatible with the expected structure and extension of the Local (Orion) and Outer (Norma-Cygnus) spiral arms in the Third Galactic Quadrant. Moreover we interpret the conspicuous intermediate-age metal poor population as belonging to the Galactic thick disk, distorted by the effect of strong disk warping at this latitude, and to the Galactic halo., Comment: 9 pages, 12 eps figures (some of them somewhat degraded in resolution), accepted for publication in MNRAS

It is widely accepted that the large obliquity of Uranus is the result of a great tangential collision (GC) with an Earth size proto-planet at the end of the accretion. We attempt to constraint the GC scenario as the cause of Uranus' obliquity as well as on the mechanisms able to give origin to the Uranian irregulars. Different capture mechanisms for irregulars operate at different stages on the giant planets formation process. The mechanisms able to capture the uranian irregulars before and after the GC are analysed. Assuming that they were captured before the GC, we calculate the orbital transfer of the nine irregulars by the impulse imparted by the GC. If their orbital transfer results dynamically implausible, they should have originated after the GC. We investigate and discuss the dissipative mechanisms able to operate later. In particular Prospero could not exist at the time of the GC. Different capture mechanisms for Prospero after the GC are investigated. Gas drag by Uranus'envelope and pull-down capture are not plausible mechanisms. Capture of Prospero through a collisionless interaction seems to be difficult. The GC itself provides a mechanism of permanent capture. However, the capture of Prospero by the GC is a low probable event. Catastrophic collisions could be a possible mechanism for the birth of Prospero and the other irregulars after the GC. Orbital and physical clusterings should then be expected. Either Prospero had to originate after the GC or the GC did not occur. In the former case, the mechanism for the origin of Prospero after the GC remains an open question. In the latter case, another theory to account for Uranus' obliquity and the formation of the Uranian regular satellites on the equatorial plane of the planet would be needed., Comment: 11 pages, 1 eps figure, accepted for publication in A&A. Abstract rephrased to fit in; V2: some problem in the latex of V1 fixed

Context. On October 24, 2007 the periodic comet 17P/Holmes underwent an astonishing outburst that increased its apparent total brightness from magnitude V\sim17 up to V\sim2.5 in roughly two days. We report on Wendelstein 0.8 m telescope (WST) photometric observations of the early evolution stages of the outburst. Aims. We studied the evolution of the structure morphology, its kinematic, and estimated the ejected dust mass. Methods. We analized 126 images in the BVRI photometric bands spread between 26/10/2007 and 20/11/2007. The bright comet core appeared well separated from that one of a quickly expanding dust cloud in all the data, and the bulk of the latter was contained in the field of view of our instrument. The ejected dust mass was derived on the base of differential photometry on background stars occulted by the moving cloud. Results. The two cores were moving apart from each other at a relative projected constant velocity of (9.87 +/- 0.07) arcsec/day (0.135 +/-0.001 km/sec). In the inner regions of the dust cloud we observed a linear increase in size at a mean constant velocity of (14.6+/-0.3) arcsec/day (0.200+/-0.004 km/sec). Evidence of a radial velocity gradient in the expanding cloud was also found. Our estimate for the expanding coma's mass was of the order of 10^{-2}-1 comet's mass implying a significant disintegration event. Conclusions. We interpreted our observations in the context of an explosive scenario which was more probably originated by some internal instability processes, rather than an impact with an asteroidal body. Due to the peculiar characteristics of this event, further observations and investigations are necessary in order to enlight the nature of the physical processes that determined it., Comment: 5 pages, 3 figures, A&A accepted

We present the results of radial velocity measurements of 770 thick disk red giants toward the South Galactic Pole, vertically distributed from 0.5 kpc to 5 kpc with respect to the Galactic plane. We find a small gradient in the vertical velocity dispersion (sigma_W) of 3.8+/-0.8 km/s kpc. Even more noteworthy, our values of $\sigma_W$ are small compared to literature values: in the middle of the vertical height range we find sigma_W(z=2kpc)=30 km/s. We found no possible explanation for this small value of sigma_W in terms of sample contamination by thin disk stars, nor by wrong assumptions regarding the metallicity distribution and the derived distances., Comment: 2 pages, 1 figure, proceeding of the XII IAU Latin American Regional Meeting

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 survey of nearby and distant clouds observed in CO. Both the optical and radio samples are the largest ones insofar present in the literature. We use this unique material to analyze the behavior of interstellar extinction and to trace the detailed structure of the Third Galactic Quadrant (TGQ).We find that the Outer (Cygnus) grand design spiral 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 = 240 degrees 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., Comment: 28 pages, 6 eps, somewhat degraded in resolution, figures. Accepted for publication in the Astrophysical Journal

The outer parts of the Milky Way disk are believed to be one of the main arenas where the accretion of external material in the form of dwarf galaxies and subsequent formation of streams is taking place. The Monoceros stream and the Canis Major and Argo over-densities are notorious examples. VLT high resolution spectra have been acquired for five distant open clusters. We derive accurate radial velocities to distinguish field interlopers and cluster members. For the latter we perform a detailed abundance analysis and derive the iron abundance [Fe/H] and the abundance ratios of several $\alpha$ elements. Our analysis confirms previous indications that the radial abundance gradient in the outer Galactic disk does not follow the expectations extrapolated from the solar vicinity, but exhibits a shallower slope. By combining the metallicity of the five program clusters with eight more clusters for which high resolution spectroscopy is available, we find that the mean metallicity in the outer disk between 12 and 21 kpc from the Galactic center is [Fe/H] $\approx -0.35$, with only marginal indications for a radial variation. In addition, all the program clusters exhibit solar scaled or slightly enhanced $\alpha$ elements, similar to open clusters in the solar vicinity and thin disk stars. We investigate whether this outer disk cluster sample might belong to an extra-galactic population, like the Monoceros ring. However, close scrutiny of their properties - location, kinematics and chemistry - does not convincingly favor this hypothesis. On the contrary, they appear more likely genuine Galactic disk clusters. We finally stress the importance to obtain proper motion measurements for these clusters to constrain their orbits., Comment: 19 pages, 9 eps figure, in press in A&A, abstract rephrased to fit in

We report on the results from an ongoing program aimed at testing Newton's law of gravity in the low acceleration regime using globular clusters. It is shown that all clusters studied so far do behave like galaxies, that is, their velocity dispersion profile flattens out at large radii where the acceleration of gravity goes below 1e-8 cm/s/s, instead of following the expected Keplerian fall off. In galaxies this behavior is ascribed to the existence of a dark matter halo. Globular clusters, however, do not contain dark matter, hence this result might indicate that our present understanding of gravity in the weak regime of accelerations is incomplete and somehow incorrect., Comment: As published on the European Southern Observatory "the Messenger", Num. 128, June 2007. Seven pages, 4 figures, 2 tables

Having already reported on the first photometric study of the intermediate-age open cluster NGC 1883 (Carraro et al. 2003), we present in this paper the first spectroscopic multi-epoch investigation of a sample of evolved stars in the same cluster. The aim is to derive the cluster membership, velocity and metallicity, and discuss recent claims in the literature (Tadross 2005) that NGC 1883 is as metal poor as globular clusters in the Halo. Besides, being one of the few outer Galactic disk intermediate-age open clusters known so far, it is an ideal target to improve our knowledge of the Galactic disk radial abundance gradient, that is a basic ingredient for any chemical evolution model of the Milky Way. The new data we obtained allow us to put NGC 1883's basic parameters more reliable. We find that the cluster has a mean metallicity of [Fe/H] = -0.20$\pm$0.22, from which we infer an age (650$^{+70}_{-70}$ Myr) close to the Hyades one and a Galactocentric distance of 12.3$^{+0.4}_{-0.2}$ kpc. The metal abundance, kinematics, and position make NGC 1883 a genuine outer disk intermediate-age open cluster. We confirm that in the outer Galactic disk the abundance gradient is shallower than in the solar vicinity., Comment: 8 pages, 7 eps figures (some degraded in resolution), accepted for publication in MNRAS

After the work of Gladman et al. (1998), it is now assessed that many irregular satellites are orbiting around Uranus. Despite many studies have been performed in past years, very few is know for the light-curves of these objects and inconsistencies are present between colours derived by different authors. This situation motivated our effort to improve both the knowledge of colours and light curves. We present and discuss time series observations of Sycorax, Prospero, Stephano, Setebos and Trinculo, five faint irregular satellites of Uranus, carried out at VLT, ESO Paranal (Chile) in the nights between 29 and 30 July, 2005 and 25 and 30 November, 2005. We derive light curves for Sycorax and Prospero and colours for all of these these bodies. For Sycorax we obtain colours B-V =0.839 +/- 0.014, V-R = 0.531 +/- 0.005 and a light curve which is suggestive of a periodical variation with period about 3.6 hours and amplitude about 0.067 +/- 0.004 mag. The periods and colours we derive for Sycorax are in agreement with our previous determination in 1999 using NTT. We derive also a light-curve for Prospero which suggests an amplitude of about 0.2 mag and a periodicity of about 4 hours. However, the sparseness of our data, prevents a more precise characterization of the light-curves, and we can not determine wether they are one-peaked or two-peaked. Hence, these periods and amplitudes have to be considered preliminary estimates. As for Setebos, Stephano and Trinculo the present data do not allow to derive any unambiguous periodicity, despite Setebos displays a significant variability with amplitude about as large as that of Prospero. Colours for Prospero, Setebos, Stephano and Trinculo are in marginal agreement with the literature., Comment: Submitted to A&A 13 Dec 2006, Accepted 17 Apr 2007. 18 pages, 8 colours figures BW printable, 6 tables. LaTeX 2.09, with packages: natbib, graphicx, longtable, aa4babbage included in the submission file (tar gzipped of 349 KBytes)

We report on the first ultracool dwarf discoveries from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release (LAS EDR), in particular the discovery of T dwarfs which are fainter and more distant than those found using the 2MASS and SDSS surveys. We aim to show that our methodologies for searching the ~27 sq degs of the LAS EDR are successful for finding both L and T dwarfs $via$ cross-correlation with the Sloan Digital Sky Survey (SDSS) DR4 release. While the area searched so far is small, the numbers of objects found shows great promise for near-future releases of the LAS and great potential for finding large numbers of such dwarfs. Ultracool dwarfs are selected by combinations of their YJH(K) UKIDSS colours and SDSS DR4 z-J and i-z colours, or, lower limits on these red optical/infrared colours in the case of DR4 dropouts. After passing visual inspection tests, candidates have been followed up by methane imaging and spectroscopy at 4m and 8m-class facilities. Our main result is the discovery following CH4 imaging and spectroscopy of a T4.5 dwarf, ULASJ 1452+0655, lying ~80pc distant. A further T dwarf candidate, ULASJ 1301+0023, has very similar CH4 colours but has not yet been confirmed spectroscopically. We also report on the identification of a brighter L0 dwarf, and on the selection of a list of LAS objects designed to probe for T-like dwarfs to the survey J-band limit. Our findings indicate that the combination of the UKIDSS LAS and SDSS surveys provide an excellent tool for identifying L and T dwarfs down to much fainter limits than previously possible. Our discovery of one confirmed and one probable T dwarf in the EDR is consistent with expectations from the previously measured T dwarf density on the sky., Comment: 7 pages, 5 figures, A&A in press

Recently, Carraro (2005) drew attention to the remarkable star cluster Whiting 1 by showing that it lies about 40 kpc from the Sun and is therefore unquestionably a member of the Galactic halo (b=-60.6 deg.). Its CMD indicated that Whiting 1 is very young (5 Gyrs) for a globular cluster. It is very likely that Whiting 1 originated in a dwarf galaxy that has since been disrupted by the Milky Way. Deep CCD photometry in the BVI pass-bands obtained with the VLT is used to improve the quality of the CMD and to determine the cluster's luminosity function and surface density profile. High-resolution spectrograms obtained with Magellan are used to measure the cluster's radial velocity and to place limits on its possible metallicity. The measurements of distance and radial velocity are used to test the cluster's membership in the stellar streams from the Sgr dSph. From our CMD of Whiting 1, we derive new estimates for the cluster's age (6.5 Gyrs), metallicity ([Fe/H]=-0.65), and distance (29.4 kpc). From echelle spectrograms of three stars, we obtain -130.6 km/s for the cluster's radial velocity and show from measurements of two infra-red CaII lines that the [Fe/H] of the cluster probably lies in the range -1.1 to -0.4. We demonstrate that the position of Whiting 1 on the sky, its distance from the Sun, and its radial velocity are identical to within the errors of both the theoretical predictions of the trailing stream of stars from the Sgr dSph galaxy and the previous observations of the M giant stars that delineate the streams. With the addition of Whiting 1, there is now strong evidence that 6 globular clusters formed within the Sgr dSph., Comment: 9 pages, 9 eps figures (some degraded in resolution), in press in Astronomy and Astrophysics. Abstract here below has been shortened to fit in

As a by-product of high-precision, ultra-deep stellar photometry in the Galactic globular cluster NGC 6397 with the Hubble Space Telescope, we are able to measure a large population of background galaxies whose images are nearly point-like. These provide an extragalactic reference frame of unprecedented accuracy, relative to which we measure the most accurate absolute proper motion ever determined for a globular cluster. We find mu_alpha = 3.56 +/- 0.04 mas/yr and mu_delta = -17.34 +/- 0.04 mas/yr. We note that the formal statistical errors quoted for the proper motion of NGC 6397 do not include possible unavoidable sources of systematic errors, such as cluster rotation. These are very unlikely to exceed a few percent. We use this new proper motion to calculate NGC 6397's UVW space velocity and its orbit around the Milky Way, and find that the cluster has made frequent passages through the Galactic disk., Comment: 5 pages including 3 figures, accepted for publication in the Astrophysical Journal Letters. Very minor changes in V2. typos fixed

Observations indicate that present-day star formation in the Milky Way disk takes place in stellar ensembles or clusters rather than in isolation. Bound, long lived stellar groups are known as open clusters. They gradually lose stars and in their final evolutionary stages they are severely disrupted leaving an open cluster remnant made of a few stars. In this paper, we study in detail the stellar content and kinematics of the poorly populated star cluster NGC1901. This object appears projected against the Large Magellanic Cloud. The aim of the present work is to derive the current evolutionary status, binary fraction, age and mass of this stellar group. These are fundamental quantities to compare with those from N-body models in order to study the most general topic of star cluster evolution and dissolution.The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC.2 catalog, and 3 epochs of high resolution spectroscopy, as well as results from extensive N-body calculations.The star group NGC1901 is found to be an ensemble of solar metallicity stars, 400+/-100 Myr old, with a core radius of 0.23 pc, a tidal radius of 1.0 pc, and located at 400+/-50 pc from the Sun. Out of 13 confirmed members, only 5 single stars have been found. Its estimated present-day binary fraction is at least 62%. The calculated heliocentric space motion of the cluster is not compatible with possible membership in the Hyades stream.Our results show that NGC1901 is a clear prototype of open cluster remnant characterized by a large value of the binary fraction and a significant depletion of low-mass stars. In the light of numerical simulations, this is compatible with NGC1901 being what remains of a larger system initially made of 500-750 stars., Comment: 13 pages, 12 eps figures (some of them degraded in resolution), accepted for publication in Astronomy and Astrophysics

The color-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud (LMC) star cluster NGC 2154 and its adjacent field, has been analyzed using Padova stellar models to determine the cluster's fundamental parameters and its Star Formation History (SFH). Deep $BR$ CCD photometry, together with synthetic CMDs and Integrated Luminosity Functions (ILFs), has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyrs, which began approximately 2.3 Gyr and ended 1.1 Gyr ago. The physical reality of such a prolonged period of star formation is however questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70%) seems to exist in NGC 2154., Comment: 12 pages, 11 figures, many of them degraded in resolution (especially Fig. 1), accepted for publication in MNRAS

The stellar populations in the outer Galactic disk are nowadays a subject of wide interest. To contribute to a better picture of this part of the Galaxy, we have studied the nature of five marginally investigated star clusters (Collinder 74, Berkeley 27, Haffner 8, NGC 2509, and VdB-Hagen 4) by means of accurate CCD photometry in the V and I pass-bands. These clusters are in fact located in the Third Galactic Quadrant. We aim to obtain the basic parameters of these objects, which in some cases are still disputed in the literature. In the case of VdB-Hagen 4 we provide the first estimate of its fundamental parameters, while for Haffner 8 we present the first CCD photometry. The analysis is based on the comparison between field stars decontaminated Color Magnitude Diagrams and stellar models. Particular care is devoted to the assessment of the data quality, and the statistical field stars decontamination. The library of stellar isochrones from Girardi et al. (2000) is adopted in this study. The analysis we carried out allowed us to solve a few inconsistencies in the literature regarding Haffner 8 and NGC 2509. Collinder 74 is found to be significantly older than reported before. VdB-Hagen 4 is a young open cluster located more than 20 kpc from the Galactic center. Such an extreme distance is compatible with the cluster belonging to the Norma-Cygnusarm., Comment: 10 pages, 17 eps figures (some of them degraded in resolution), in press in Astronomy and Astrophysics

A test of Newton's law of gravity in the low acceleration regime using globular clusters is presented. New results for the core collapsed globular cluster NGC 7099 are given. The run of the gravitational potential as a function of distance is probed studying the velocity dispersion profile of the cluster, as derived from a set of 125 radial velocities with accuracy better than 1 km/s. The velocity dispersion profile is traced up to ~18 pc from the cluster center. The dispersion is found to be maximal at the center, then decrease until 10+-2 pc from the center, well inside the cluster tidal radius of 42 pc. After that the dispersion remains constant with average value 2.2+-0.3 km/s. Assuming for NGC 7099 a total V mag of M(V)=-7.43 mags and mass-to-light ratio M/L=1, the acceleration at 10 pc from the center is 1.1e-8 cm/s/s. Thus, the flattening of the velocity dispersion profile occurs for a value of the internal acceleration of gravity fully consistent with a_0=1.2e-8 cm/s/s observed in galaxies. This new result for NGC 7099 brings to 4 the clusters with velocity dispersion profile probing acceleration below a_0. All four have been found to have a flat dispersion profile at large radii where the acceleration is below a_0, mimicking qualitatively and quantitatively elliptical galaxies. Whether this indicates a failure of Newtonian dynamics in the low acceleration limit or some more conventional dynamical effect (e.g., tidal heating) is still unclear. However, the similarities emerging between very different globular clusters, as well as between globular clusters and elliptical galaxies seem to favor the first of these two possibilities., Comment: Accepted for publication in A&A Letters. Four pages in total

We perform a detailed photometric study of the stellar populations in a Galactic Field at l = 232, b = -6 in the Canis Major (CMa) constellation. We present the first U,B,V,I photometry of the old open cluster Auner1 and determine it to be 3.25 Gyr old and to lie at 8.9 kpc from the Sun. In the background of the cluster, at more than 9 kpc, we detect a young population most probably associated to the Norma Cygnus spiral arm. Furthermore, we detect the signature of an older population and identify its Turn Off and Red Giant Branch. This population is found to have a mean age of 7 Gyrs and a mean metallicity of Z = 0.006 . We reconstruct the geometry of the stellar distribution and argue that this older population - often associated to the Canis Major {\it galaxy}- belongs in fact to the warped old thin/thick disk component along this line of sight., Comment: 19 pages, 7 eps figures (some degraded), accepted for publication in the Astronomical Journal

The dwarf planet Eris (2003 UB313, formerly known also as ``Xena'') is the largest KBO up to now discovered. Despite being larger than Pluto and bearing many similarities with it, it has not been possible insofar to detect any significant variability in its light curve, preventing the determination of its period and axial ratio. We attempt to assess the level of variability of the Eris light curve by determining its BVRI photometry with a target accuracy of 0.03 mag/frame in R and a comparable or better stability in the calibration. Eris has been observed between November $30^\mathrm{th}$ and December $5^\mathrm{th}$ 2005 with the Y4KCam on-board the 1.0m Yale telescope at Cerro Tololo Interamerican Observatory, Chile in photometric nights. We obtain 7 measures in B, 23 in V, 62 in R and 20 in I. Averaged B, V, and I magnitudes as colors are in agreement within $\approx 0.03$ mag with measures from Rabinowitz et al. (2006) taken in the same nights. Night-averaged magnitudes in R shows a statistically significant variability over a range of about $0.05\pm0.01$ mag. This can not be explained by known systematics, background objects or some periodical variation with periods less than two days in the light-curve. The same applies to B, V and to less extent to I due to larger errors. In analogy with Pluto and if confirmed by future observations, this ``long term'' variability might be ascribed to a slow rotation of Eris, with periods longer than 5 days, or to the effect of its unresolved satellite ``Dysnomea'' which may contribute for $\approx0.02$ mag to the total brightness., Comment: 7 pages, 3 eps figures, accepted for publication as Astronomy and Astrophysics Letter

We present improved values of the three components of the absolute space velocity of the open cluster NGC6791. One HST ACS/WFC field with two-epoch observations provides astrometric measurements of objects in a field containing the cluster center. Identification of 60 background galaxies with sharp nuclei allows us to determine an absolute reference point, and measure the absolute proper motion of the cluster. We find (mu_alpha cos(delta), mu_delta)_J2000.0 = (-0.57+/-0.13, -2.45+/-0.12)mas/yr, and adopt V_rad = -47.1+/-0.7km/s from the average of the published values. Assuming a Galactic potential, we calculate the Galactic orbit of the cluster for various assumed distances, and briefly discuss the implications on the nature and the origin of this peculiar cluster., Comment: 5 pages, 3 figures, 3 tables. Accepted for publication in A&A Letters, on October 18th 2006

We present first results from a deep (J = 18.7), wide-field (6.5 square degrees) infrared (ZYJHK) survey in the Upper Sco association conducted within the science verification phase of the UKIRT Infrared Deep Sky Survey Galactic Cluster Survey (GCS). Cluster members define a sequence well separated from field stars in the (Z-J,Z) colour-magnitude diagram. We have selected a total of 164 candidates with J = 10.5-18.7 mag from the (Z-J,Z) and (Y-J,Y) diagrams. We further investigated the location of those candidates in the other colour-magnitude and colour-colour diagrams to weed out contaminants. The cross-correlation of the GCS catalogue with the 2MASS database confirms the membership of 116 photometric candidates down to 20 Jupiter masses as they lie within a 2 sigma circle centred on the association mean motion. The final list of cluster members contains 129 sources with masses between 0.3 and 0.007 Msun. We extracted a dozen new low-mass brown dwarfs below 20 Mjup, the limit of previous surveys in the region. Finally, we have derived the mass function in Upper Sco over the 0.3-0.01 Msun mass range, best fit by a single segment with a slope of index alpha = 0.6+/-0.1, in agreement with previous determination in open clusters., Comment: 14 pages, 9 figures, 7 tables, 2 appendices; accepted to MNRAS

Aims: This paper presents a new homogeneous catalogue of blue straggler stars (BSS) in Galactic open clusters. Methods: Photometric data for 216 clusters were collected from the literature and 2782 BSS candidates were extracted from 76 of them. Results: We found that the anticorrelation of BSS frequency vs. total magnitude identified in similar studies conducted on Galactic globular clusters extends to the open cluster regime: clusters with smaller total magnitude tend to have higher BSS frequencies. Moreover, a clear correlation between the BSS frequency (obtained normalising the total number of BSS either to the total cluster mass or, for the older clusters, to the total number of clump stars) and the age of the clusters was found. A simple model is developed here to try to explain this last and new result. The model allows us to ascertain the important effect played by mass loss in the evolution of open clusters.

In this paper we present the first $BVI$ CCD photometry of six overlooked old open clusters (Berkeley 44, NGC 6827, Berkeley 52, Berkeley 56, Skiff 1 and Berkeley 5) and derive estimates of their fundamental parameters by using isochrones from the Padova library (Girardi et al. 2000). We found that all the clusters are older than the Hyades, with ages ranging from 0.8 (NGC 6827 and Berkeley 5) to 4.0 (Berkeley 56) Gyr. This latter is one of the old open clusters with the largest heliocentric distance. In the field of Skiff 1 we recognize a faint blue Main Sequence identical to the one found in the background of open clusters in the Second and Third Galactic Quadrant, and routinely attributed to the Canis Major accretion event. We use the synthetic Color Magnitude Diagram method and a Galactic model to show that this population can be easily interpreted as Thick Disk and Halo population toward Skiff 1. We finally revise the old open clusters age distribution, showing that the previously suggested peak at 5 Gyr looses importance as additional old clusters are discovered., Comment: in publication in MNRAS

In this paper we present a new, accurate determination of the three components of the absolute space velocity of the Galactic globular cluster NGC6397 (l 338d, b -12d). We used three HST/WFPC2 fields with multi-epoch observations to obtain astrometric measurements of objects in three different fields in this cluster. The identification of 33 background galaxies with sharp nuclei allowed us to determine an absolute reference point and measure the absolute proper motion of the cluster. The third component has been obtained from radial velocities measured on spectra from the multi-fiber spectrograph FLAMES at UT2-VLT. We find [mu_alpha cos(delta), mu_delta](J2000.0) = [+3.39 +/- 0.15, -17.55 +/- 0.15] mas/yr, and V_rad = +18.36 +/- 0.09 (+/-0.10) km/s. Assuming a Galactic potential, we calculate the cluster orbit for various assumed distances, and briefly discuss the implications., Comment: 7 pages, 5 figures, 4 tables. Accepted for publication in A&A, on April 27 2006

(Abridged) We derive the structure of the Galactic stellar Warp and Flare using 2MASS RC and RGB stars, selected at mean heliocentric distances of 3, 7 and 17 kpc. Our results are: (i) a clear stellar warp signature is derived for the 3 selected rings; (ii) the derived stellar warp is consistent (both in amplitude and phase-angle) with that for the Galactic interstellar dust and HI gas; (iii) the Sun seems not to fall on the line of nodes. The stellar warp phase-angle orientation (+15 degrees) is close to the orientation angle of the Galactic bar and this produces an asymmetric warp for the inner rings; (iv) a Northern/Southern warp symmetry is observed only for the ring at 17 kpc; (v) treating a mixture of thin and thick disk populations we trace the disk flaring and derive a constant scale-height (~0.65 kpc) within R(GC)~15 kpc. Further out, the disk flaring increase gradually reaching a mean scale-height of ~1.5 kpc at R(GC)~23 kpc; and (vi) these results provide further robust evidence that there is no disk radial truncation at R(GC)~14 kpc. In the particular case of the Canis Major over-density we confirm its coincidence with the Southern stellar maximum warp occurring near l=240. We present evidence to conclude that all observed parameters (e.g. number density, radial velocities, proper motion etc) of CMa are consistent with it being a normal Milky Way outer-disk population, thereby leaving no justification for a more complex interpretations of its origin. The present analysis does not provide a conclusive test of the structure or origin of the Monoceros Ring. Nevertheless, we show that a warped flared Milky Way contributes significantly at the locations of the Monoceros Ring., Comment: 25 pages, 22 figures, accepted for publication in A&A. A higher resolution pdf file is available at http://wwwuser.oat.ts.astro.it/zaggia/public_html/warp/

With the discovery of the Sagittarius dwarf spheroidal (Ibata et al. 1994), a galaxy caught in the process of merging with the Milky Way, the hunt for other such accretion events has become a very active field of astrophysical research. The identification 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 direction of the constellation of Canis Major (CMa, Martin et al. 2004), apparently associated to the ring, has led to the widespread belief that a second galaxy being cannibalised by the Milky Way had been found. In this scenario, the overdensity would be the remaining core of the disrupted galaxy and the ring would be the tidal debris left behind. However, unlike the Sagittarius dwarf, which is well below the Galactic plane and whose orbit, and thus tidal tail, is nearly perpendicular to the plane of the Milky Way, 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 show that our new description of the Milky Way leads to a completely different picture. We argue that the Norma-Cygnus spiral arm defines a distant stellar ring crossing Monoceros and the overdensity is simply a projection effect of looking along the nearby local arm. Our perspective sheds new light on a very poorly known region, the third Galactic quadrant (3GQ), where CMa is located., Comment: 5 pages, 2 figures. Quality of Fig 1 has been degraded to make it smaller. Original fig. available on request. accepted for publication in MNRAS letters

CCD BVI photometry is presented for 7 previously unstudied star clusters projected toward the inner side of the Galaxy: Trumpler 23, Lynga 3, Collinder 307, Ruprecht 134, ESO552SC16, AL 5 and Kronberger 3. Color magnitude diagrams of the cluster regions allow us to conclude that Lynga 3 and ESO552SC16, are not clusters, but groups of bright stars probably located in the Carina-Sagittarius spiral arm. AL 5 and Kronberger 3 are so embedded in a dense stellar field that we cannot confirm their nature. Trumpler~ 3 and Ruprecht 134 are two intermediate-age open clusters located well inside the solar ring which deserve further attention. Finally, Collinder 307 is an obscured younger cluster (250 Myr) located in the Carina-Sagittarius spiral arm. Our results emphasize the difficulty to search for open clusters in the inner regions of the Galaxy due to the richness of the field and the patchy nature of the interstellar absorption, but at the same time significantly contribute to a better understanding of this complicated regions of the Milky Way., Comment: 11 pages, 16 degraded eps figures, in press in MNRAS

We report on high resolution Echelle spectroscopy of 20 giant stars in the Galactic old open clusters NGC 6791 obtained with Hydra at the WIYN telescope. High precision radial velocity allow us to isolate 15 {\it bona fide} cluster members. From 10 of them we derive a global [M/H]=+0.39$\pm$0.05. We therefore confirm that NGC 6791 is extremely metal rich, exhibits a few marginally sub-solar abundance ratios, and within the resolution of our spectra does not show evidences of spread in metal abundance. With these new data we re-derive the cluster fundamental parameters suggesting that it is about 8 Gyr old and 4.3 kpc far from the Sun. The combination of its chemical properties, age, position, and Galactic orbit hardly makes NGC 6791 a genuine Population I open cluster. We discuss possible interpretations of the cluster peculiarities suggesting that the cluster might be what remains of a much larger system, whose initial potential well could have been sufficient to produce high metallicity stars, and which has been depopulated by the tidal field of the Galaxy. Alternatively, its current properties may be explained by the perturbation of the Galactic bar on an object originated well inside the solar ring, where the metal enrichment had been very fast., Comment: 29 pages, 10 eps figure, accepted for publication in the Astrophysical Journal

Based on a deep optical CCD (UBV(RI)_C) photometric survey and on the Two-Micron All-Sky-Survey (2MASS) data we derived the main parameters of the open cluster NGC 2401. We found this cluster is placed at 6.3 $\pm$ 0.5 kpc (V_O - M_V = 14.0 \pm 0.2) from the Sun and is 25 Myr old, what allows us to identify NGC 2401 as a member of the young population belonging to the innermost side of the extension of the Norma-Cygnus spiral--arm in the Third Galactic Quadrant. A spectroscopic study of the emission star LSS 440 that lies in the cluster area revealed it is a B0Ve star; however, we could not confirm it is a cluster member. We also constructed the cluster luminosity function (LF) down to $V \sim 22$ and the cluster initial mass function (IMF) for all stars with masses above $M \sim 1-2 M_{\sun}$. It was found that the slope of the cluster IMF is $x \approx 1.8 \pm 0.2$. The presence of a probable PMS star population associated to the cluster is weakly revealed., Comment: 10 paginas, 11 eps figures, accepted for publication in MNRAS

The first CCD UBV(RI) photometric study in the area of the doubtful open cluster NGC 2129 is presented. Photometry of a field offset 15 arcmin northward is also provided, to probe the Galactic disk population toward the cluster. Using star counts, proper motions from the UCAC2 catalog, colour-magnitude and colour-colour diagrams we demonstrate that NGC 2129 is a young open cluster. The cluster radius is 2.5 arcmin, and across this region we find evidence of significant differential reddening, although the reddening law seems to be normal toward its direction. Updated estimates of the cluster fundamental parameters are provided. The mean reddening is found to be E(B-V)=0.80$\pm$0.08 and the distance modulus is $(m-M)_o$= 11.70$\pm0.30$. Hence, NGC 2129 is located at 2.2$\pm$0.2 kpc from the Sun inside the Local spiral arm. The age derived from 37 photometrically selected members is estimated to be approximately 10 million years. These stars are used to provide new estimates of the cluster absolute proper motion components., Comment: 8 pages, 11 figures, in press in MNRAS

Eighteen RR Lyrae variables (RRLs) that lie in the "$12\fh 4$ clump" identified by the QUEST survey have been observed spectroscopically to measure their radial velocities and metal abundances. Ten blue horizontal branch (BHB) stars identified by the Sloan Digital Sky Survey (SDSS) were added to this sample. Six of the 9 stars in the densest region of the clump have a mean radial velocity in the galactic rest frame ($V_{\rm gsr}$) of 99.8 and $\sigma$ = 17.3 ${\rm km s}^{-1}$, which is slightly smaller than the average error of the measurements. The whole sample contains 8 RRLs and 5 BHB stars that have values of $V_{\rm gsr}$ suggesting membership in this stream. For 7 of these RRLs, the measurements of [Fe/H], which have an internal precision of 0.08 dex, yield $<{\rm [Fe/H]}> = -1.86$ and $\sigma$ = 0.40. These values suggest that the stream is a tidally disrupted dwarf spheroidal galaxy of low luminosity. Photometry from the database of the SDSS indicates that this stream covers at least 106 deg$^2$ of the sky in the constellation Virgo. The name Virgo Stellar Stream is suggested., Comment: Replaced with revised version accepted for publication in ApJ Letters 13 pages 4 figures

Relying on U,B imagery at the Italian Telescopio Nazionale Galileo (TNG), we report here the discovery of a sample of 13 new UV-bright post-HB candidate stars in the field of the galactic open cluster NGC 6791. Owing to its super-solar metal content ([Fe/H]>0.2 dex) and estimated age (t> 8 Gyr), this cluster represents the nearest and ideal stellar aggregate to match the distinctive properties of the evolved stellar populations possibly ruling the UV-upturn phenomenon in elliptical galaxies and bulges of spirals. Our ongoing spectroscopic follow-up of this unique UV-bright sample will allow us to assess - once cluster membership of the candidates is properly checked - the real nature (e.g. SdB, SdO, AGB-manque' or EHB stars) of these hot sources, and their link with the ultraviolet excess emerging from low-mass, metal-rich evolutionary environments of external galaxies., Comment: To appear in Baltic Astronomy. Proceedings of the 2nd meeting on Hot Subdwarf Stars, La Palma, June 2005. 4 pages, 2 figures. For larger information about this topic, see http://www.bo.astro.it/~eps/buz10502/10502.html

We analyse CCD broad band (UBV(RI)c) photometric data obtained in the fields of the poorly studied open clusters NGC 2425 and NGC 2635. Both clusters are found to be of intermediate age thus increasing the population of open clusters known to be of the age of, or older than, the Hyades. More explicitly, we find that NGC 2425 is a 2.2 Gyr old cluster, probably of solar metallicity, located at 3.5 kpc from the Sun. NGC 2635 is a Hyades age (600 Myr) cluster located at a distance of 4.0 kpc from the Sun. Its Colour Magnitude Diagram reveals that it is extremely metal poor for its age and position, thus making it a very interesting object in the context of Galactic Disk chemical evolution models., Comment: 10 pages, 13 figures. Figure quality has been quiet degraded. Accepted by A&A

CCD $BVI$ photometry is presented for 8 previously unstudied star clusters located in the First and Fourth Galactic Quadrants: AL~1, BH 150, NGC 5764, Lynga~9, Czernik~37, BH 261, Berkeley~80 and King~25. Color magnitude diagrams of the cluster regions suggest that several of them (BH 150, Lynga~9, Czernik~37 and BH 261 and King~25) are so embedded in the dense stellar population toward the galactic center that their properties, or even their existence as physical systems, cannot be confirmed. Lynga~9, BH 261 and King~25 appear to be slight enhancements of dense star fields, BH 150 is probably just a single bright star in a dense field, and Czernik~37 may be a sparse, but real cluster superimposed on the galactic bulge population. We derive preliminary estimates of the physical parameters for the remaining clusters. AL~1 appears to be an intermediate age cluster beyond the solar circle on the far side of the galaxy and the final two clusters, NGC 5764 and Berkeley 80 are also of intermediate age but located inside the solar ring. This set of clusters highlights the difficulties inherent in studying the stellar populations toward the inner regions of the galaxy., Comment: 9 pages, 12 eps figures, in press in MNRAS

We report the detection of a young stellar population ($\leq$100 Myrs) in the ba ckground of 9 young open clusters belonging to a homogenoeous sample of 30 star clusters in the Third Galactic Quadrant (at $217^o \leq l \leq 260^o$). 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 3 intermediate-age open clusters and suggested to be a $\leq$ 1-2 Gyr old population belonging to the Canis Major (CMa) over-density (Bellazzini et al. 2004, Mart\'inez-Delgado et al. 2005). However, we find that the young population in those three and in six clusters of our sample follows remarkably well the pattern of the Norma-Cygnus spiral arm as defined by CO clouds, while in the other three program clusters it lies in the Perseus arm. We finally provide one example (out of 21) of a cluster which does not show any background population, demonstrating that this population is not ubiquitous toward CMa., Comment: 13 pages, 3 eps figure, the first one HUGELY reduced in resolution, accepted for publication as ApJ Letter

CCD BVI photometry of the faint open clusters Berkeley~73, Berkeley~75 and Berkeley~25 are presented. The two latter are previously unstudied clusters to our knowledge. While Berkeley~73 is found to be of intermediate-age (about 1.5 Gyr old), Berkeley~75 and Berkeley~25 are two old clusters, with ages larger than 3.0 Gyr. We provide also estimates of the clusters size. Very interestingly, all these clusters turn out to lie far away from the Galactic Center, at $R_{GC} \geq$ 16 kpc, and quite high onto the Galactic plane, at $|Z_{\odot}| \geq 1.5$ kpc. They are therefore important targets to probe the properties of the structure of the Galaxy in this direction, where the Canis Major over-density has been recently discovered to be located., Comment: 8 pages, 10 figures, in press in A&A

We present the first $BVI$ CCD photometry to $V=22.0$ of 4 fields centered on the region of the southern Galactic star clusters Ruprecht~61, Czernik~32, NGC 2225 and NGC 2262 and of 4 displaced control fields. These clusters were never studied before, and we provide for the first time estimates of their fundamental parameters, namely radial extent, age, distance and reddening. We find that the four clusters are all of intermediate age (around 1 Gyr), close to the Sun and possess lower than solar metal abundance., Comment: 10 pages, 14 figures, in press in MNRAS

Wide field BVI photometry and $^{12}$CO(1$\to$0) observations are presen ted in the region of the open cluster NGC 6520 and the dark molecular cloud Barnard~86. From the analysis of the optical data we find that the cluster is rather compact, with a radius of 1.0$\pm$0.5 arcmin, smaller than previous estimates. The cluster age is 150$\pm$50 Myr and the reddening E$_{B-V}$=0.42$\pm$0.10. The distance from the Sun is estimated to be 1900$\pm$100 pc, and it is larger than previous estimates. We finally derive basic properties of the dark nebula Barnard 86 on the assumption that it lies at the same distance of the cluster., Comment: 21 pages, 8 eps figures (a few degraded in resolution), accepted for publication in the Astronomical Journal

We report on high resolution spectroscopy of four giant stars in the Galactic old open clusters Berkeley~22 and Berkeley~66 obtained with HIRES at the Keck telescope. We find that $[Fe/H]=-0.32\pm0.19$ and $[Fe/H]=-0.48\pm0.24$ for Berkeley~22 and Berkeley~66, respectively. Based on these data, we first revise the fundamental parameters of the clusters, and then discuss them in the context of the Galactic disk radial abundance gradient. We found that both clusters nicely obey the most updated estimate of the slope of the gradient from \citet{fri02} and are genuine Galactic disk objects., Comment: 20 pages, 6 eps figures, accepted for publication in the Astronomical Journal

We report on $BVI$ CCD photometry to $V=22.0$ for 3 fields centered on the region of the Galactic star clusters Ruprecht~4, Ruprecht~7 and Pismis~15 and on 3 displaced control fields. Ruprecht~4 and Pismis~15 have never been studied before, and we provide for the first time estimates of their fundamental parameters, namely, radial extent, age, distance and reddening. Ruprecht~7 (Berkeley~33) however was studied by Mazur et al. (1993). We find that the three clusters are all of intermediate age (0.8-1.3 Gyr), and with a metallicity close to or lower than solar., Comment: 8 pages, 12 eps figures, in press in MNRAS

e present wide field deep UBVI photometry for the previously unstudied open cluster NGC 4852 down to a limiting magnitude $I\sim24$, obtained from observations taken with the Wide Field Imager camera on-board the MPG/ESO 2.2m telescope at La Silla (ESO, Chile). These data are used to obtain the first estimate of the cluster basic parameters, to study the cluster spatial extension by means of star counts, and to derive the Luminosity (LF) and Mass Function (MF). The cluster radius turns out to be $5.0\pm1.0$ arcmin. The cluster emerges clearly from the field down to V=20 mag. At fainter magnitud es, it is completely confused with the general Galactic disk field. The stars inside this region define a young open cluster (200 million years old) 1.1 kpc far from the Sun (m-M = 11.60, E(B-V) = 0.45). The Present Day Mass Functions (PDMF) from the $V$ photometry is one of the most extended in mass insofar obtained, and can be represented as a power-law with a slope $\alpha = 2.3\pm0.3$ and (the Salpeter (1955) MF in this notation has a slope $\alpha = 2.35$), in the mass range $3.2 \leq \frac{m}{m_{\odot}} \leq 0.6$. Below this mass, the MF cannot be considered as representative of the cluster MF, as the cluster merges with the field and therefore the MF is the result of the combined effect of strong irregularities in the stellar background and interaction of the cluster with the dense Galactic field. The cluster total mass at the limiting magnitude results to be 2570$\pm$210 M$_{\odot}$., Comment: 9 pages, 10 eps figures (some degraded in resolution), accepted for publication in A&A

We report on $BVI$ CCD photometry of a field centered in the region of the Galactic star cluster Whiting~1 down to $V=23.0$. This cluster has never been studied insofar, and we provide for the first time estimates of its fundamental parameters, namely, radial extent, age, distance and reddening. Whiting~1 turns out to be a compact star cluster with a diameter of about 1$^{\prime}$. We find that the cluster is about 5 Gyr old and has a probable metal abundance around [Fe/H]= -1.20. Its position at $b=-60^{o}.64$ and at a heliocentric distance of about 45 kpc makes the cluster a rather strange object, surely not a disk old open cluster, but perhaps the youngest halo Globular Cluster insofar known., Comment: 16 pages, 7 eps figure, accepted for publication as ApJ Letter

We discuss the nature of eleven Possible Open Cluster Remnants (POCRs) by using absolute proper motions from the Southern Proper Motion (SPM) Program 3 (Girard et al. 2004) combined with near infrared photometry from 2MASS. The analysis is done by considering the distribution of stars in the Color-Magnitude and the Vector Point diagrams. We successfully probed the capabilities of the SPM catalog to detect a physical group by looking at the open cluster Blanco~1. However, within the uncertainties of the SPM3 catalog and basing on 2MASS photometry we conclude that only one -ESO282SC26- out of eleven objects turns out to be a probable physical group. We suggest it is an open cluster 1.3 Gyr old and located 1.4 kpc from the Sun., Comment: 9 pages, 18 eps figures, in press in Astronomy and Astrophysics

Having shown in a recent paper that the main sequence of omega Centauri is split into two distinct branches, we now present spectroscopic results showing that the bluer sequence is_less_ metal-poor. We have carefully combined GIRAFFE@VLT spectra of 17 stars on each side of the split into a single spectrum for each branch, with adequate S/N to show clearly that the stars of the blue main sequence are less metal poor by 0.3 dex than those of the dominant red one. From an analysis of the individual spectra, we could not detect any abundance spread among the blue main sequence stars, while the red main sequence stars show a 0.2 dex spread in metallicity. We use stellar-structure models to show that only greatly enhanced helium can explain the color difference between the two main sequences, and we discuss ways in which this enhancement could have arisen., Comment: 24 pages, 7 figures, The Astrophysical Journal, accepted 30 Nov. 2004

We report on $VI$ CCD photometry of two fields centered in the region of the open clusters NGC 6404 and NGC 6583 down to $V=22.0$. These clusters have never been studied insofar, and we provide for the first time estimates of their fundamental parameters, namely, radial extent, age, distance and reddening. We find that NGC 6404 radius is 2.0 arcmin, as previously proposed, while NGC 6583 radius is 1.0 arcmin, significantly lower than previous estimates. Both clusters turn out to be of intermediate age (0.5-1.0 Gyr old), and located inside the solar ring, at a Galactocentric distance of about 6.5 kpc. These results make these objects very interesting targets for spectroscopic follow-up to measure their metallicity. In fact they might allow us to enlarge by more than 1 kpc the baseline of the radial abundance gradient in the Galactic disk toward the Galactic Center direction. This baseline is currently rather narrow especially for clusters of this age., Comment: 9 pages, 9 eps figures, in press in MNRAS

We present CCD UBVI photometric and medium/high resolution spectroscopic observations obtained in the field of the previously unstudied dissolving open cluster candidates NGC 5385, NGC 2664 and Collinder~21. Our analysis stands on the discussion of star counts, photometry, radial velocity distribution, and proper motions available from the Tycho~2 catalogue. All the three aggregates clearly emerge from the mean Galactic field, but, regrettably, the close scrutiny of proper motions and radial velocities reveals that we are not facing any physical group. Instead, what we are looking at are just chance alignments of a few bright unrelated stars. Our analysis casts some doubt on the Bica et al. (2001) criterion to look for Possible Open Cluster Remnants. It seems mandatory to define a better criterion to adopt for further investigations., Comment: 12 pages, 12 eps figures (7, 9 and 11 degraded in resolution), accepted for publication in Astronomy & Astrophysics