Milky Way Millennium Nucleus

Santiago, Chile

Milky Way Millennium Nucleus

Santiago, Chile

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Chene A.-N.,University of Valparaíso | Chene A.-N.,University of Concepción | Borissova J.,University of Valparaíso | Clarke J.R.A.,University of Valparaíso | And 21 more authors.
Astronomy and Astrophysics | Year: 2012

Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Aims. The VVV observations will foster the construction of a sample of Galactic star clusters with reliable and homogeneously derived physical parameters (e.g., age, distance, and mass, etc.). In this first paper in a series, the methodology employed to establish cluster parameters for the envisioned database are elaborated upon by analysing four known young open clusters: Danks 1, Danks 2, RCW 79, and DBS 132. The analysis offers a first glimpse of the information that can be gleaned from the VVV observations for clusters in the final database. Methods. Wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results. Results are inferred from VVV near-infrared photometry and numerous low resolution spectra (typically more than 10 per cluster). The high quality of the spectra and the deep wide-field VVV photometry enables us to precisely and independently determine the characteristics of the clusters studied, which we compare to previous determinations. An anomalous reddening law in the direction of the Danks clusters is found, specifically E(J - H)/E(H - Ks) = 2.20 ± 0.06, which exceeds published values for the inner Galaxy. The G305 star forming complex, which includes the Danks clusters, lies beyond the Sagittarius-Carina spiral arm and occupies the Centaurus arm. Finally, the first deep infrared colour-magnitude diagram of RCW 79 is presented, which reveals a sizeable pre-main sequence population. A list of candidate variable stars in G305 region is reported. Conclusions. This study demonstrates the strength of the dataset and methodology employed, and constitutes the first step of a broader study which shall include reliable parameters for a sizeable number of poorly characterised and/or newly discovered clusters. © ESO, 2012.


Chene A.-N.,University of Valparaíso | Chene A.-N.,University of Concepción | Borissova J.,University of Valparaíso | Bonatto C.,Federal University of Rio Grande do Sul | And 25 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims. This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods. Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results. We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 103 M™) clusters. They are highly obscured (AV ∼ 5-24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ∼30-50 M™ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters. © 2013 ESO.


Catelan M.,University of Santiago de Chile | Minniti D.,University of Santiago de Chile | Lucas P.W.,University of Hertfordshire | Dekany I.,University of Santiago de Chile | And 41 more authors.
Proceedings of the International Astronomical Union | Year: 2014

The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is an ongoing time-series, near-infrared (IR) survey of the Galactic bulge and an adjacent portion of the inner disk, covering 562 square degrees of the sky, using ESO's VISTA telescope. The survey has provided superb multi-color photometry in 5 broadband filters (Z, Y, J, H, and Ks), leading to the best map of the inner Milky Way ever obtained, particularly in the near-IR. The main part of the survey, which is focused on the variability in the Ks-band, is currently underway, with bulge fields observed between 34 and 73 times, and disk fields between 34 and 36 times. When the survey is complete, bulge (disk) fields will have been observed up to a total of 100 (60) times, providing unprecedented depth and time coverage in the near-IR. Here we provide a first overview of stellar variability in the VVV data. Copyright © International Astronomical Union 2014.


Ivanov V.D.,European Southern Observatory | Minniti D.,University of Santiago de Chile | Minniti D.,Andrés Bello University | Minniti D.,Vatican Observatory | And 20 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.


Soto M.,University of La Serena | Barba R.,University of La Serena | Barba R.,CONICET | Gunthardt G.,University of La Serena | And 28 more authors.
Astronomy and Astrophysics | Year: 2013

The new multi-epoch near-infrared VISTA Variables in the Vía Láctea (VVV) survey is sampling 562 deg2 of the Galactic bulge and adjacent regions of the disk. Accurate astrometry established for the region surveyed allows the VVV data to be merged with overlapping surveys (e.g., GLIMPSE, WISE, 2MASS, etc.), thereby enabling the construction of longer baseline spectral energy distributions for astronomical targets. However, in order to maximize use of the VVV data, a set of transformation equations are required to place the VVV JHKs photometry onto the 2MASS system. The impetus for this work is to develop those transformations via a comparison of 2MASS targets in 152 VVV fields sampling the Galactic disk. The transformation coefficients derived exhibit a reliance on variables such as extinction. The transformed data were subsequently employed to establish a mean reddening law of EJ-H/EH-Ks = 2.13 ± 0.04, which is the most precise determination to date and merely emphasizes the pertinence of the VVV data for determining such important parameters. © 2013 ESO.


Saito R.K.,Federal University of Sergipe | Minniti D.,Milky Way Millennium Nucleus | Minniti D.,University of Santiago de Chile | Minniti D.,Vatican Observatory | And 8 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.


Salgado C.,University of Concepción | Moni Bidin C.,University of Concepción | Moni Bidin C.,Católica del Norte University | Villanova S.,University of Concepción | 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.


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.


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.

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