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Ivanov V.D.,European Southern Observatory | Minniti D.,University of Santiago de Chile | Minniti D.,Andres Bello University | Hempel M.,University of Santiago de Chile | And 19 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The severe crowding in the direction of the inner Milky Way suggests that the census of stars within a few tens of parsecs in that direction may not be complete. Aims. We searched for new nearby object companions of known high proper motion (HPM) stars located towards the densest regions of the southern Milky Way where the background contamination presented a major problem to previous observations. Methods. The common proper motion (PM) method was used. We inspected the area around 167 known HPM (≥200 mas yr-1) stars: 67 in the disk and 100 in the bulge. Multi-epoch images were provided by the Two Micron All Sky Survey (2MASS) and the VISTA Variables in Via Lactea (VVV). The VVV is a new on-going ZYJHKS plus multi-epoch K S survey of ~562 deg2 of the Milky Way bulge and inner southern disk. Results. Seven new co-moving companions were discovered around known HPM stars (L 149-77, LHS 2881, L 200-41, LHS 3188, LP 487-4, LHS 5333, and LP 922-16); six known co-moving pairs were recovered (LTT 5140 A + LTT 5140 B, L 412-3 + L 412-4, LP 920-25 + LP 920-26, LTT 6990 A + LTT 6990 B, M 124.22158.2900 + M 124.22158.2910, and GJ 2136 A + GJ 2136 B); a pair of stars that was thought to be co-moving was found to have different proper motions (LTT 7318, LTT 7319); published HPMs of eight stars were not confirmed (C* 1925, C* 1930, C* 1936, CD-60 4613, LP 866-17, OGLE BUL-SC20 625107, OGLE BUL-SC21 298351, and OGLE BUL-SC32 388121); last but not least, spectral types ranging from G8V to M5V were derived from new infrared spectroscopy for seventeen stars, members of the co-moving pairs. Conclusions. The seven newly discovered stars constitute ~4% of the nearby HPM star list, but this is not a firm limit on the HPM star incompleteness because our starting point - the HPM list assembled from the literature - is incomplete itself, missing many nearby HPM M- and L-type objects, and it is contaminated with non-HPM stars. We have demonstrated that the superior sub-arcsec spatial resolution, with respect to previous surveys, allows the VVV to examine in greater detail the binary nature nature of known HPM stars. The ≥5 yr span of VVV will provide a sufficient baseline for finding new HPM stars from VVV data alone. © ESO 2013. Source

Catelan M.,University of Santiago de Chile | Leyton P.P.,University of Santiago de Chile | Saito R.K.,Milky Way Millennium Nucleus | Saito R.K.,Federal University of Sergipe | And 3 more authors.
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2014

Reddening-free indices represent a powerful, and yet little used, approach to problems where reddening/extinction constitute a serious issue, without having to deal with the extinction of any individual star. Here we report on our progress in obtaining reddening-free indices, in the VISTA filter system. Source

Kuehn C.A.,Michigan State University | Kuehn C.A.,University of Sydney | Dame K.,Michigan State University | Smith H.A.,Michigan State University | And 10 more authors.
Astronomical Journal | Year: 2013

This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. The primary goal of this series is to look at how the characteristics and behavior of RR Lyrae stars in Oosterhoff-intermediate systems compare to those of their counterparts in Oosterhoff-I/II systems. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We found a total of 32 variables stars (22 RRab, 4 RRc, and 6 RRd stars) in our field of view. We present photometric parameters and light curves for these stars. We also present physical properties, derived from Fourier analysis of light curves, for some of the RR Lyrae stars. We discuss the Oosterhoff classification of Reticulum and use our results to re-derive the distance modulus and age of the cluster. © 2013. The American Astronomical Society. All rights reserved. Source

Salgado C.,University of Concepcion | Moni Bidin C.,University of Concepcion | Moni Bidin C.,Catolica del Norte University | Villanova S.,University of Concepcion | And 3 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Recent investigations revealed very peculiar properties of blue horizontal branch (HB) stars in ω Centauri, which show anomalously low surface gravity and mass compared to other clusters and to theoretical models. ω Centauri, however, is a very unusual object, hosting a complex mix of multiple stellar populations with different metallicity and chemical abundances. Aims. We measured the fundamental parameters (temperature, gravity, and surface helium abundance) of a sample of 71 blue HB stars in M 22, with the aim of clarifying if the peculiar results found in ω Cen are unique to this cluster. M 22 also hosts multiple sub-populations of stars with a spread in metallicity, analogous to ω Cen. Methods. The stellar parameters were measured on low-resolution spectra fitting the Balmer and helium lines with a grid of synthetic spectra. From these parameters, the mass and reddening were estimated. Results. Our results on the gravities and masses agree well with theoretical expectations, matching the previous measurements in three "normal" clusters. The anomalies found in ω Cen are not observed among our stars. A mild mass underestimate is found for stars hotter than 14 000 K, but an exact analogy with ω Cen cannot be drawn. We measured the reddening in the direction of M 22 with two independent methods, finding E(B-V) = 0.35 ± 0.02 mag, with semi-amplitude of the maximum variation Δ(E(B-V)) = 0.06 mag, and an rms intrinsic dispersion of σ(E(B-V)) = 0.03 mag. © 2013 ESO. Source

Saito R.K.,Federal University of Sergipe | Minniti D.,Milky Way Millennium Nucleus | Minniti D.,University of Santiago de Chile | Catelan M.,Milky Way Millennium Nucleus | And 7 more authors.
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2014

VVV is an ongoing near-IR, multi-band, time-series survey of the Galactic bulge and plane. Here we summarize the first results from a search for variability in selected fields of the VVV bulge area. Source

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