Photometry of the five marginally studied open clusters Collinder 74, Berkeley 27, Haffner 8, NGC 2509 and VdB-Hagen 4

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 Astrophysic

NGC 4337: an over-looked old cluster in the inner disc of the Milky Way

Galactic open clusters do not survive long in the high density regions of the inner Galactic disc. Inside the solar ring only 11 open clusters are known with ages older than one Gyr. We show here, basing on deep, high-quality photometry, that NGC 4337, contrary to earlier findings, is indeed an old open cluster. The cluster is located very close to the conspicuous star cluster Trumpler 20, as well mis-classified in the past, and that has received so much attention in recent years. NGC 4337 shows a significant clump of He-burning stars which was not detected previously. Its beautiful color-magnitude diagram is strikingly similar to the one of the classical old open clusters IC 4651, NGC 752, and NGC 3680, and this suggests similar age and composition. A spectroscopic study is much needed to confirm our findings. This, in turn, would also allow us to better define the inner disc radial abundance gradient and its temporal evolution.To this aim, a list of clump star candidates is provided.Comment: 5 pages, 4 eps figures, in press as MNRAS Lette

The Metallicity of the Open Cluster Tombaugh 2

We investigate the nature of the chemical composition of the outer disc open cluster Tombaugh 2, that a recent study by Frinchaboy et al. (2008) suggested to possess an intrinsic metal abundance dispersion. We aim to investigate such claims by high resolution spectra obtained for a number of stars in the Tombaugh 2 field, together with independent UBVIc photometry. The spectra, together with input atmospheric parameters and model atmospheres, are used to determine detailed chemical abundances for a variety of elements in 13 members having good spectra. We find the mean metallicity to be [Fe/H]=-0.31+-0.02 with no evidence for an intrinsic abundance dispersion, in contrary to the recent results of Frinchaboy et al. (2008). We find Ca and Ba to be slightly enhanced while Ni and Sc are solar. The r-process element Eu was found to be enhanced, giving an average [Eu/Ba]=+0.17. The Li abundance decreases with Teff on the upper giant branch and maintains a low level for red clump stars. The mean metallicity we derive is in good agreement with that expected from the radial abundance gradient in the disc for a cluster at its Galactocentric distance. The surprising result found by Frinchaboy et al. (2008), that is the presence of 2 distinct abundance groups within the cluster, implying either a completely unique open cluster with an intrinsic metallicity spread, or a very unlikely superposition of a cold stellar stream and a very distant open cluster, is not supported by our new result.Comment: 11 pages, 5 eps figures, in press on A&

Old Main-Sequence Turnoff Photometry in the Small Magellanic Cloud. I. Constraints on the Star Formation History in Different Fields

We present ground-based B and R-band color-magnitude diagrams (CMDs), reaching the oldest main-sequence turnoffs with good photometric accuracy for twelve fields in the Small Magellanic Cloud (SMC). Our fields, located between ~1 and ~4 degrees from the center of the galaxy, are situated in different parts of the SMC such as the "Wing'' area, and towards the West and South. In this paper we perform a first analysis of the stellar content in our SMC fields through comparison with theoretical isochrones and color functions (CFs). We find that the underlying spheroidally distributed population is composed of both intermediate-age and old stars and that its age composition does not show strong galacto-centric gradients. The three fields situated toward the east, in the Wing region, show very active current star formation. However, only in the eastern field closest to the center do we find an enhancement of recent star formation with respect to a constant SFR(t). The fields corresponding to the western side of the SMC present a much less populated young MS, and the CF analysis indicates that the SFR(t) greatly diminished around 2 Gyr ago in these parts. Field smc0057, the closest to the center of the galaxy and located in the southern part, shows recent star formation, while the rest of the southern fields present few bright MS stars. The structure of the red clump in all the CMDs is consistent with the large amount of intermediate-age stars inferred from the CMDs and color functions. None of the SMC fields presented here are dominated by old stellar populations, a fact that is in agreement with the lack of a conspicuous horizontal branch in all these SMC CMDs. This could indicate that a disk population is ruling over a possible old halo in all the observed fields.Comment: To appear in A

The thickening of the thin disk in the third Galactic quadrant

In the third Galactic quadrant (180 < l < 270) of the Milky Way, the Galactic thin disk exhibits a significant warp ---shown both by gas and young stars--- bending down a few kpc below the formal Galactic plane (b=0). This warp shows its maximum at 240, in the direction of the Canis Major constellation. In a series of papers we have traced the detailed structure of this region using open star clusters, putting particular emphasis on the spiral structure of the outer disk. We noticed a conspicuous accumulation of young star clusters within 2-3 kpc from the Sun and close to b=0, that we interpreted as the continuation of the Local (Orion) arm towards the outer disk. While most clusters (and young stars in their background) follow closely the warp of the disk, our decade-old survey of the spiral structure of this region led us to identify three clusters, Haffner~18(1 and 2) and Haffner~19, which remain very close to b=0 and lie at distances (4.5, 8.0, and 6.4 kpc) where most of the material is already significantly warped. Here we report on a search for clusters that share the same properties as Haffner~18 and 19, and investigate the possible reasons for such an unexpected occurrence. We present UBVRI photometry of 5~young clusters, namely NGC~2345, NGC~2374, Trumpler~9, Haffner~20, and Haffner~21, which also lie close to the formal Galactic plane. With the exception of Haffner~20, in the background of these clusters we detected young stars that appear close to b=0, and are located at distances up to 8 kpc from the Sun, thus deviating significantly from the warp. These populations define a structure that distributes over almost the entire third Galactic quadrant. We discuss this structure in the context of a possible thin disk flaring, in full similarity with the Galactic thick disk.Comment: 53 pages, 12 eps figures, in press in the Astronomical Journa

Speckle interferometry at SOAR in 2019

The results of speckle interferometric observations at the 4.1 m Southern Astrophysical Research Telescope (SOAR) in 2019 are given, totaling 2555 measurements of 1972 resolved pairs with separations from 15 mas (median 0.21") and magnitude difference up to 6 mag, and non-resolutions of 684 targets. We resolved for the first time 90 new pairs or subsystems in known binaries. This work continues our long-term speckle program. Its main goal is to monitor orbital motion of close binaries, including members of high-order hierarchies and Hipparcos pairs in the solar neighborhood. We give a list of 127 orbits computed using our latest measurements. Their quality varies from excellent (25 orbits of grades 1 and 2) to provisional (47 orbits of grades 4 and 5).Comment: Accepted by The Astronomical Journal. 10 pages, 5 Figures. Measurements and non-resolutions, published electronically, are available from the first author. arXiv admin note: substantial text overlap with arXiv:1905.1043

Proper motions of Local Group dwarf spheroidal galaxies I: First ground-based results for Fornax

In this paper we present in detail the methodology and the first results of a ground-based program to determine the absolute proper motion of the Fornax dwarf spheroidal galaxy. The proper motion was determined using bona-fide Fornax star members measured with respect to a fiducial at-rest background spectroscopically confirmed Quasar, \qso. Our homogeneous measurements, based on this one Quasar gives a value of (\mua,\mud)$= (0.64 \pm 0.08, -0.01 \pm 0.11)$ \masy. There are only two other (astrometric) determinations for the transverse motion of Fornax: one based on a combination of plates and HST data, and another (of higher internal precision) based on HST data. We show that our proper motion errors are similar to those derived from HST measurements on individual QSOs. We provide evidence that, as far as we can determine it, our motion is not affected by magnitude, color, or other potential systematic effects. Last epoch measurements and reductions are underway for other four Quasar fields of this galaxy, which, when combined, should yield proper motions with a weighted mean error of $\sim50\,\mu$as y$^{-1}$, allowing us to place important constraints on the orbit of Fornax.Comment: Accepted for publication in Publications of the Astronomical Society of the Pacific, PASP. To appear in July issue. 64 pages, 18 figure

The Star Formation History in a SMC field: IAC-star/IAC-pop at work

We present a progress report of a project to study the quantitative star formation history (SFH) in different parts of the Small Magellanic Cloud (SMC). We use the information in [(B-R), R] color-magnitude diagrams (CMDs), which reach down to the oldest main-sequence turnoffs and allow us to retrieve the SFH in detail. We show the first results of the SFH in a SMC field located in the Southern direction (at $\thicksim$1 kpc from the SMC center). This field is particularly interesting because in spite of being located in a place in which the HI column density is very low, it still presents a recent enhancement of star formation.Comment: Poster presented at: Stellar Populations as Building Blocks of Galaxies, Proceedings IAU Symposium No. 241, 200

Properties of the open cluster Tombaugh 1 from high resolution spectroscopy and uvbyCaHβ\beta photometry

Open clusters can be the key to deepen our knowledge on various issues involving the structure and evolution of the Galactic disk and details of stellar evolution because a cluster's properties are applicable to all its members. However the number of open clusters with detailed analysis from high resolution spectroscopy and/or precision photometry imposes severe limitation on studies of these objects. To expand the number of open clusters with well-defined chemical abundances and fundamental parameters, we investigate the poorly studied, anticenter open cluster Tombaugh 1. Using precision uvbyCaH$\beta$ photometry and high resolution spectroscopy, we derive the cluster's properties and, for the first time, present detailed abundance analysis of 10 potential cluster stars. Using radial position from the cluster center and multiple color indices, we have isolated a sample of unevolved probable, single-star members of Tombaugh 1. The weighted photometric metallicity from $m_1$ and $hk$ is [Fe/H] = -0.10 $\pm$ 0.02, while a match to the Victoria-Regina Str\"{o}mgren isochrones leads to an age of 0.95 $\pm$ 0.10 Gyr and an apparent modulus of $(m-M)$ = 13.10 $\pm$ 0.10. Radial velocities identify 6 giants as probable cluster members and the elemental abundances of Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Y,Ba, Ce, and Nd have been derived for both the cluster and the field stars. Tombaugh 1 appears to be a typical inner thin disk, intermediate-age open cluster of slightly subsolar metallicity, located just beyond the solar circle, with solar elemental abundance ratios except for the heavy s-process elements, which are a factor of two above solar. Its metallicity is consistent with a steep metallicity gradient in the galactocentric region between 9.5 and 12 kpc. Our study also shows that Cepheid XZ CMa is not a member of Tombaugh 1, and reveals that this Cepheid presents signs of barium enrichment.Comment: 74 pages, 15 figures, 13 tables; Accepted for publication in A