I. Dékány

The multiperiodic Blazhko modulation of CZ Lacertae

A thorough analysis of the multicolour CCD observations of the RRab-type variable, CZ Lacertae, is presented. The observations were carried out in two consecutive observing seasons in 2004 and 2005 within the framework of the Konkoly Blazhko Survey of bright, northern, short-period RRab variables. The O − C variation of CZ Lac indicated that a significant period decrease took place just around the time of the CCD observations. Our data gave a unique opportunity to study the related changes in the pulsation and modulation properties of a Blazhko star in detail. Two different period components (≈ 14.6 and ≈ 18.6 d) of the Blazhko modulation were identified. Both modulation components had similar strength. The periods and amplitudes of the modulations changed significantly from the first season to the next, while the mean pulsation amplitude decreased slightly. The modulation frequencies were in a 5:4 resonance ratio in the first observing season, and then the frequencies shifted in opposite directions, and their ratio was close to the 4:3 resonance in the next season. The interaction of the two modulations caused beating with a period of 74 d in the first season, which resembled the 4-yr-long cycle of the ≈ 40-d modulation of RR Lyr. The mean values of the global physical parameters and their changes with the Blazhko phase of both modulation components were determined by the inverse photometric method.

Variable stars in the VVV globular clusters. I. 2MASS-GC 02 and Terzan 10

The VISTA Variables in the V?a L?ctea (VVV) ESO Public Survey is opening a new window to study inner Galactic globular clusters (GCs) using their variable stars. These GCs have been neglected in the past due to the difficulties caused by the presence of elevated extinction and high field stellar densities in their lines of sight. However, the discovery and study of any present variables in these clusters, especially RR Lyrae stars, can help to greatly improve the accuracy of their physical parameters. It can also help to shed some light on the questions raised by the intriguing Oosterhoff dichotomy in the Galactic GC system. In a series of papers we plan to explore variable stars in the GCs falling inside the field of the VVV survey. In this first paper, we search for and study the variables present in two highly reddened, moderately metal-poor, faint, inner Galactic GCs: 2MASS-GC 02 and Terzan 10. We report the discovery of sizable populations of RR Lyrae stars in both GCs. We use near-infrared period?luminosity relations to determine the color excess of each RR Lyrae star, from which we obtain both accurate distances to the GCs and the ratios of the selective-to-total extinction in their directions. We find the extinction toward both clusters to be elevated, non-standard, and highly differential. We also find both clusters to be closer to the Galactic center than previously thought, with Terzan 10 being on the far side of the Galactic bulge. Finally, we discuss their Oosterhoff properties, and conclude that both clusters stand out from the dichotomy followed by most Galactic GCs.

THE VVV SURVEY REVEALS CLASSICAL CEPHEIDS TRACING A YOUNG AND THIN STELLAR DISK ACROSS THE GALAXY’S BULGE

Solid insight into the physics of the inner Milky Way is key to understanding our Galaxys evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years.

The VVV Templates Project Towards an automated classification of VVV light-curves - I. Building a database of stellar variability in the near-infrared

Context. The Vista Variables in the Via Lactea (VVV) ESO Public Survey is a variability survey of the Milky Way bulge and an adjacent section of the disk carried out from 2010 on ESO Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey will eventually deliver a deep near-IR atlas with photometry and positions in five passbands (ZY JHKS) and a catalogue of 1−10 million variable point sources – mostly unknown – that require classifications. Aims. The main goal of the VVV Templates Project, which we introduce in this work, is to develop and test the machine-learning algorithms for the automated classification of the VVV light-curves. As VVV is the first massive, multi-epoch survey of stellar variability in the near-IR, the template light-curves that are required for training the classification algorithms are not available. In the first paper of the series we describe the construction of this comprehensive database of infrared stellar variability. Methods. First, we performed a systematic search in the literature and public data archives; second, we coordinated a worldwide observational campaign; and third, we exploited the VVV variability database itself on (optically) well-known stars to gather high-quality infrared light-curves of several hundreds of variable stars. Results. We have now collected a significant (and still increasing) number of infrared template light-curves. This database will be used as a training-set for the machine-learning algorithms that will automatically classify the light-curves produced by VVV. The results of such an automated classification will be covered in forthcoming papers of the series.Context. The Vista Variables in the Via Lactea (VVV) ESO Public Survey is a variability survey of the Milky Way bulge and an adjacent section of the disk carried out from 2010 on ESO Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey will eventually deliver a deep near-IR atlas with photometry and positions in five passbands (ZYJHKS) and a catalogue of 1−10 million variable point sources – mostly unknown – that require classifications. Aims. The main goal of the VVV Templates Project, which we introduce in this work, is to develop and test the machine-learning algorithms for the automated classification of the VVV light-curves. As VVV is the first massive, multi-epoch survey of stellar variability in the near-IR, the template light-curves that are required for training the classification algorithms are not available. In the first paper of the series we describe the construction of this comprehensive database of infrared stellar variability. Methods. First, we performed a systematic search in the literature and public data archives; second, we coordinated a worldwide observational campaign; and third, we exploited the VVV variability database itself on (optically) well-known stars to gather high-quality infrared light-curves of several hundreds of variable stars. Results. We have now collected a significant (and still increasing) number of infrared template light-curves. This database will be used as a training-set for the machine-learning algorithms that will automatically classify the light-curves produced by VVV. The results of such an automated classification will be covered in forthcoming papers of the series.

New RR Lyrae variables in binary systems

Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated (O−C) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide O−C diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that ≳4 per cent of the RRL reside in binary systems.

Bulge RR Lyrae stars in the VVV tile b201

1 Instituto de Astrofisica, Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, Casilla 306, Santiago, Chile e-mail: fgran@astro.puc.cl 2 Millennium Institute of Astrophysics (MAS), Santiago, Chile 3 Departamento de Ciencias Fisicas, Universidad Andres Bello, Republica 220, Santiago, Chile 4 Vatican Observatory, 00120 Vatican City State, Italy 5 Universidade Federal de Sergipe, Departamento de Fisica, Av. Marechal Rondon s/n, 49100-000 Sao Cristovao, SE, Brazil 6 Jordell Bank Centre for Astrophysics, Alan Turing Building, Manchester, M13 9PL, UK

A near-infrared catalogue of the Galactic novae in the VVV survey area

Context. Near-infrared data on classical novae contain useful information about the ejected gas mass and the thermal emission by dust formed during eruption, and provide independent methods to classify the objects according to the colour of their progenitors, and the fading rate and features seen after eruption. The VISTA Variables in the V�a L�ctea survey (VVV) is a near-IR ESO Public Survey mapping the Milky Way bulge and southern plane. Data taken during 2010-2011 covered the entire area in the JHK s bands plus some epochs in K s -band of the ongoing VVV variability campaign. Aims: We used the VVV data to create a near-IR catalogue of the known Galactic novae in the 562 sq. deg. area covered by VVV. We also compiled the information about novae from the variability tables of the VVV variability campaign. Methods: We used the novae list provided by VSX/AAVSO catalogue to search for all objects within the VVV area. From the 140 novae, we were able to retrieve the JHK s colours of 93 objects. We also checked in the ongoing VVV variability campaign for the light curves of novae that erupted in the last years. Results: The VVV near-IR catalogue of novae contains JHK s photometry of 93 objects completed as of December 2012. VVV allows to monitor objects within up to ?K s ~ 10 mag range. VVV images can also be used to discover and study novae by searching for the expanding shell. Since objects are seen at different distances and reddening levels, the colour-magnitude and colour-colour diagrams show the novae spread in magnitude as well as in colour. Dereddened colours and reddening-free indices were used with caution and cannot be a good approach in all cases since the distance and spectral features prevent more conclusive results for some extreme objects. Light curves for some recent novae are presented. Conclusions: Thanks to its high spatial resolution in the near IR and wide K s -range, the VVV survey can be a major contributor to the search for and study of novae in the most crowded and high-extinction regions of the Milky Way. The VVV survey area contains ~35% of all known novae in the Galaxy. Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002.

A machine learned classifier for RR Lyrae in the VVV survey

Variable stars of RR Lyrae type are a prime tool with which to obtain distances to old stellar populations in the Milky Way. One of the main aims of the Vista Variables in the Via Lactea (VVV) near-infrared survey is to use them to map the structure of the Galactic Bulge. Owing to the large number of expected sources, this requires an automated mechanism for selecting RR Lyrae, and particularly those of the more easily recognized type ab (i.e., fundamental-mode pulsators), from the 10 6 −10 7 variables expected in the VVV survey area. In this work we describe a supervised machine-learned classifier constructed for assigning a score to a K s -band VVV light curve that indicates its likelihood of being ab -type RR Lyrae. We describe the key steps in the construction of the classifier, which were the choice of features, training set, selection of aperture, and family of classifiers. We find that the AdaBoost family of classifiers give consistently the best performance for our problem, and obtain a classifier based on the AdaBoost algorithm that achieves a harmonic mean between false positives and false negatives of ≈7% for typical VVV light-curve sets. This performance is estimated using cross-validation and through the comparison to two independent datasets that were classified by human experts.

Absolute parameters of AE For – a highly active detached binary of late K type

We present photometric and spectroscopic analysis of AE For - a detached eclipsing binary composed of two late K dwarfs. The masses of the components are found to be 0.6314 ± 0.0035 and 0.6197 ± 0.0034 Mand the radii to be 0.67 ± 0.03 and 0.63 ± 0.03 Rfor primary and secondary component, respectively. Both components are significantly oversized compared to theoretical models, which we attribute to their high activity. They show Hα ,H β, Hγ , Ca H and Ca K in emission, and are heavily spotted, causing large variations of the light curve.

Near-infrared photometry and spectroscopy of the low Galactic latitude globular cluster 2MASS-GC 03

We present deep near-infrared photometry and spectroscopy of the globular cluster 2MASS-GC03 projected in the Galactic disk using MMIRS on the Clay telescope (Las Campanas Observatory) and VISTA Variables in the Via Lactea survey (VVV) data. Most probable cluster member candidates were identified from near-infrared photometry. Out of ten candidates that were followed-up spectroscopically, five have properties of cluster members, from which we calculate = -0.9 +- 0.2 and a radial velocity of v_r > = -78 +- 12km/s. A distance of 10.8kpc is estimated from 3 likely RRLyrae members. Given that the cluster is currently at a distance of 4.2kpc from the Galactic center, the clusters long survival time of an estimated 11.3 +- 1.2Gyr strengthens the case for its globular-cluster nature. The cluster has a hint of elongation in the direction of the Galactic center.