Browsing by Author "Papageorgiou, A."

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    An investigation of low-mass-ratio EW systems from the Catalina Sky Survey
    (SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST, 2020) Lalounta, E.; Papageorgiou, A.; Christopoulou, P. E.; Catelan, M.
    We have conducted a survey of overcontact binary systems (EW) with mass ratio <= 0.25 from the Catalina Sky Survey (CSS) that are considered strong merger candidates and are probable progenitors of FK Com-type stars and blue stragglers. The discovery of such extreme mass ratio overcontact binaries is vital to resolve the critical mass ratio ambiguity to merge, the mass loss process, and to refine the current theoretical models. So far only a few tens of such systems have been identified. To increase this sample, we selected and derived the physical parameters (mass, temperature and radius ratios, inclination and fill-out factor, along with their respective uncertainties) of 92 newly discovered totally eclipsing low-mass-ratio (LMR) EW systems based on their VCSS light curves, using PHOEBE-0.31a scripter and Monte Carlo methods.
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    Recovering Algol-type eclipsing binaries in the CRTS
    (2020) Carmo, A.; Ferreira Lopes, C. E.; Papageorgiou, A.; Jablonski, F. J.; Rodrigues, C. V.; Drake, A. J.; Cross, N. J. G.; Catelan , Marcio
    Eclipsing binary systems are relevant to astronomy since they provide primary means of determining fundamental stellar astrophysical quantities such as mass, radius, and temperature of the components. Algol-type eclipsing binaries (EAs) have spherical or slightly ellipsoidal components and are generally systems that produce light curves with narrow eclipses and few points within the eclipse. The most current photometric surveys usually have observation cadences larger than these eclipses duration, which hinders the detection of EAs. The variability of these objects can even be detected, but the period is rarely found because an optimized constraint is required. Thereby, we used a new methodology to find new EAs in the Catalina Real-Time Transient Survey. As a result, we determined periodicity for 56\% of EA$_\mathrm{up}$ (EAs marked as having unknown period), which corresponds to 87 new EAs reported. Also, we use color criteria to select a subsample that contains 8 low-mass binary systems with spectral types K and M. To obtain the individual physical parameters of these components, each light curve was modeled with the Wilson & Devinney light curve synthesis code combined with a Monte Carlo Markov chain process. The results were examined in the scenario of radius inflation of low-mass stars in binary systems....
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    Recovering variable stars in large surveys: EAup Algol-type class in the Catalina Survey
    (OUP, 2020) Carmo, A.; Ferreira Lopes, C. E.; Papageorgiou, A.; Jablonski, F. J.; Rodrigues, C. V.; Drake, A. J.; Cros, N. J. G.; Catelan, Márcio
    The discovery and characterization of Algol eclipsing binaries (EAs) provide an opportunity to contribute for a better picture of the structure and evolution of low-mass stars. However, the cadence of most current photometric surveys hinders the detection of EAs since the separation between observations is usually larger than the eclipse(s) duration and hence few measurements are found at the eclipses. Even when those objects are detected as variable, their periods can be missed if an appropriate oversampling factor is not used in the search tools. In this paper, we apply this approach to find the periods of stars catalogued in the Catalina Real-Time Transient Survey (CRTS) as EAs having unknown period (EA up ). As a result, the periods of ∼56percent of them were determined. Eight objects were identified as low-mass binary systems and modelled with the Wilson & Devinney synthesis code combined with a Markov chain Monte Carlo optimization procedure. The computed masses and radii are in agreement with theoretical models and show no evidence of inflated radii. This paper is the first of a series aiming to identify suspected binary systems in large surveys.
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    The VVV Infrared Variability Catalog (VIVA-I)
    (2020) Ferreira Lopes, E. C.; Cross, N. J. G.; Catelan, M.; Minniti, D.; Hempel, M.; Lucas, W. P.; Angeloni, R.; Jablonsky, F.; Braga, F. V.; Leao, C. I.; Herpich, F. R.; Alonso-Garcia, J.; Papageorgiou, A.; Pichara, K.; Saito, K. R.; Bradley, A.; Beamin Muhlenbrock Juan Carlos; Cortes, C.; De Medeiros, J. R.; Russell, Christopher
    Thanks to the VISTA Variables in the Via Lactea (VVV) ESO Public Survey it is now possible to explore a large number of objects in those regions. This paper addresses the variability analysis of all VVV point sources having more than 10 observations in VVVDR4 using a novel approach. In total, the near-IR light curves of 288,378,769 sources were analysed using methods developed in the New Insight Into Time Series Analysis project. As a result, we present a complete sample having 44, 998, 752 variable star candidates (VVV-CVSC), which include accurate individual coordinates, near-IR magnitudes (ZYJHKs), extinctions A(Ks), variability indices, periods, amplitudes, among other parameters to assess the science. Unfortunately, a side effect of having a highly complete sample, is also having a high level of contamination by non-variable (contamination ratio of non-variables to variables is slightly over 10:1). To deal with this, we also provide some flags and parameters that can be used by the community to de-crease the number of variable candidates without heavily decreasing the completeness of the sample. In particular, we cross-identified 339,601 of our sources with Simbad and AAVSO databases, which provide us with information for these objects at other wavelegths. This sub-sample constitutes a unique resource to study the corresponding near-IR variability of known sources as well as to assess the IR variability related with X-ray and Gamma-Ray sources. On the other hand, the other 99.5% sources in our sample constitutes a number of potentially new objects with variability information for the heavily crowded and reddened regions of the Galactic Plane and Bulge. The present results also provide an important queryable resource to perform variability analysis and to characterize ongoing and future surveys like TESS and LSST.
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    What we can learn from eclipsing binaries in large surveys: The case of EA Catalina systems
    (2020) Papageorgiou, A.; Christopoulou, P. -E.; Catelan, Marcio; Drake, A. J.; Djorgovski, S. G.
    With the recent availability of large-scale multi-epoch photometric datasets, we were able to study EBs en masse. Large samples are useful to determine not only statistical properties but for finding strange and curious systems that no one had ever studied before, binaries with peculiarities that may reveal physical significance. We present an updated and more detailed catalog of 4680 Northern EAs in the Catalina Sky Survey (CSS). This work includes, new systems, revised period determination and ephemerides, system morphology classification based on machine learning techniques, computation of principal physical parameters with the EBAI (Eclipsing Binary via Artificial Intelligence) and detection of eclipse timing variations. We identify several groups of interesting systems including those with low mass K and M dwarfs, systems with longterm modulation of the maximum brightness, systems with longterm period modulation, potential triple systems and systems with magnetic activity....