Browsing by Author "Papageorgiou, Athanasios"

Now showing 1 - 7 of 7
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    A Study of Nine Extremely Low Mass Ratio-contact Binary Systems
    (IOP Publishing Ltd, 2024) Lalounta, Eleni; Christopoulou, Panagiota-Eleftheria; Papageorgiou, Athanasios; Ferreira Lopes, C. E.; Catelan, Marcio
    Low-mass ratio systems (LMR) are a very interesting class of contact eclipsing binaries challenging the theoretical models of stability. These systems are also considered possible progenitors of the rare low-mass optical transients called red novae. In this study, we present the identification of 7 new totally eclipsing LMR systems from Catalina Sky Surveys (CSS) and 77 LMR candidates from the All Sky Automated Survey. Using the available CSS light curves and new multiband observations for CSS_J210228.3-031048 and CSS_J231513.3+345335 with the 2.3 m Aristarchos telescope at Helmos Observatory, we estimate their physical and absolute parameters and investigate their stability and their progenitors. The light curves are analyzed by performing a two-dimensional scan on the mass-ratio inclination plane with Phoebe-0.31 scripter, while the errors are estimated using Monte Carlo simulations and heuristic scanning of the parameter space. Our analysis revealed that all 9 CSS systems have extreme mass ratios from 0.09 to 0.16. Our statistical analysis of well-studied LMR contact binaries shows that LMR systems tend to have warmer and more massive primaries. The investigation of the progenitors of both low and higher-mass-ratio systems reveals a trend for the former to originate from higher-mass ancestors. Finally, we investigate the stability condition by calculating the ratio of spin angular momentum to orbital angular momentum and other stability indicators in the context of the reliability of the solutions.
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    An Updated Catalog of 4680 Northern Eclipsing Binaries with Algol-type Light-curve Morphology in the Catalina Sky Surveys
    (2018) Papageorgiou, Athanasios; Catelan, Márcio; Christopoulou, Panagiota-Eleftheria; Drake, Andrew J.; Djorgovski, S. G.
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    Detection of period variations of eclipsing binaries in the Catalina Sky Survey
    (2021) Papageorgiou, Athanasios; Catelan, Márcio; Christopoulou, Panagiota-Eleftheria; Drake, Andrew J.; Djorgovski, S. G.
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    Eclipsing binary stars in the era of massive surveys first results and future prospects
    (2017) Papageorgiou, Athanasios; Catelan, Márcio; Ramos Contreras, Rodrigo; Drake, Andrew J.
    Our thinking about eclipsing binary stars has undergone a tremendous change in the last decade. Eclipsing binary stars are one of nature's best laboratories for determining the fundamental physical properties of stars and thus for testing the predictions of theoretical models. Some of the largest ongoing variable star surveys include the Catalina Real-time Transient Survey (CRTS) and the VISTA Variables in the Vía Láctea survey (VVV). They both contain a large amount of photometric data and plenty of information about eclipsing binaries that wait to be extracted and exploited. Here we briefly describe our efforts in this direction....
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    New low mass ratio contact binaries in the Catalina Sky Survey
    (2022) Christopoulou, Panagiota-Eleftheria; Lalounta, Eleni; Papageorgiou, Athanasios; Ferreira Lopes, C. E.; Catelan, Márcio; Drake, Andrew J.
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    Physical Parameters of Northern Eclipsing Binaries in the Catalina Sky Survey
    (2019) Papageorgiou, Athanasios; Catelan, Márcio; Christopoulou, Panagiota-Eleftheria; Drake, Andrew J.; Djorgovski, S. G.
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    Relative evolution of eclipsing binaries: A tool for measuring globular cluster ages and He abundances
    (2024) Cristi Cambiaso, Nicolas Eduardo; Catelan, Márcio; Valcarce, Aldo; Papageorgiou, Athanasios
    Context. Globular clusters (GCs) are among the oldest objects in the Universe for which an age can be directly measured; they thus play an important cosmological role. This age depends sensitively on the He abundance, however, which cannot be reliably measured from spectroscopy in GC stars. Detached eclipsing binaries (DEBs) near the turnoff (TO) point may play an important role in this regard. Aims. The aim of this study is to explore the possibility that, by working with differential measurements of stars that comprise a TO binary system and by assuming the two stars have the same age and He abundance, one can achieve tighter, more robust, and less model-dependent constraints on the ages and He abundances than otherwise possible by working with the absolute parameters of the stars. Methods. We compared both the absolute and differential parameters of the stars in V69, a TO DEB pair in the GC 47 Tuc, with two different sets of stellar evolutionary tracks, making use of a Monte Carlo technique to estimate the GC's He abundance and age, along with their uncertainties. Results. We find that the relative approach can produce age and He abundance estimates that are in good agreement with those from the literature. We show that our estimates are also less model-dependent, less sensitive to [Fe/H], and more robust to inherent model systematics than those obtained with an absolute approach. On the other hand, the relative analysis results in larger statistical uncertainties than its absolute counterpart, at least in the case of V69, where the two stars have very similar properties. For binary pairs in which one of the components is less evolved than the other, the statistical uncertainty can be reduced. Conclusions. Our results suggest that the method proposed in this work can be used to robustly constrain the He abundance and ages of GCs.