Browsing by Author "Jurcsik, Johanna"

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    A Data-driven Study of RR Lyrae Near-IR Light Curves: Principal Component Analysis, Robust Fits, and Metallicity Estimates
    (2018) Hajdu, Gergely; Dekany, Istvan; Catelan, Márcio; Grebel, Eva K.; Jurcsik, Johanna
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    Continued Search of RR Lyrae Binary Systems Towards the Galactic Bulge
    (2018) Hajdu, Gergely; Catelan, Márcio; Jurcsik, Johanna; Thompson, Ian B.
    Binary systems provide the most straightforward way of measuring the mass of individual stars, and through it, constraining the models of stellar evolution. Unfortunately, very few binary candidates containing RR Lyrae variables have been found previously. We continue our search for such systems in the photometric data of the OGLE survey towards the Galactic bulge, finding more than 30 such candidates. Furthermore, we show that our ongoing radial velocity follow-up observations have the potential to confirm or refute some of our candidates in the near future....
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    Multiple populations in M3: chemical abundances in AGB stars
    (2015) Alves, Sanzia; Contreras Ramos, Rodrigo; Amigo, Pia; Valcarce, Aldo A. R.; Cortés, Cristian; Hajdu, Gergely; Jurcsik, Johanna; Zoccali, Manuela; Catelan, Márcio
    Since the discovery of multiple populations in globular clusters, it is widely accepted that most globulars have at least two populations that can be classified in terms of their Na abundance, with the Na-poor stars belonging to the first stellar population, and the Na-rich stars to a second population. In the case of NGC 6752, it has been found that all the Na-rich stars fail to reach the asymptotic giant branch (AGB) phase, thus suggesting that the second-generation stars in this cluster all become so-called AGB-manqué stars after a hot horizontal branch (HB) phase. In contrast, stars belonging to both populations are present on the AGB phase in 47 Tucanae, which is consistent with the lack of a sizeable population of very hot HB stars in this cluster. In this contribution, we use high-resolution spectra obtained with UVES@VLT to analyze the chemical behavior of AGB stars in M3 (NGC 5272), a globular cluster with an HB morphology intermediate between those of NGC 6752 and 47 Tuc, to check whether second-generation stars in this cluster undergo an AGB-manqué phase as in NGC 6752, or whether instead they are able to successfully reach the AGB, as seen in 47 Tuc....
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    Properties of RR Lyrae variables in binary systems: towards a first-time mass measurement
    (2022) Hajdu, Gergely; Pietrzyński, Grzegorz; Catelan, Marcio; Jurcsik, Johanna; Karczmarek, Paulina; Pilecki, Bogumił; Thompson, Ian
    Despite their general usefulness as distance indicators and tracers of old stellar populations, several properties of RR Lyrae variable stars remain poorly understood. Crucially, the most basic stellar parameter, the stellar mass, has never been measured for any member of this class. We performed a new search for RR Lyrae variables in binary systems, looking for the light travel-time effect in the long-term light curves obtained by the OGLE project toward the Galactic bulge, finding 87 high-confidence candidates. The distributions of the inferred properties of these binary systems are quite peculiar: no system has a binary period below 1000d, and their frequency peaks between 3000 and 4000d; their eccentricities are strongly concentrated around 0.27; and their mass functions are apparently trimodal. Supposing an isotropic inclination distribution, and a mass of 0.65 times solar for a typical RR Lyrae, these three modes point to typical companion masses of ~0.6, ~0.2 and ~0.067 solar masses. These can be attributed to a combination of main sequence and white dwarf, red dwarf, and brown dwarf companions, respectively. As RR Lyrae variables are evolved from (close to) solar mass, Population II main sequence stars, their binary parameters provide a unique glimpse into the binary properties of the old stellar population. These properties seem to be wildly different from those of Population I binaries. The difference in the distribution of binary periods can be explained tentatively by binary stellar evolution and selection effects. However, the distribution of eccentricities, and especially the trimodal companion mass distribution is in stark contrast to Population I binary parameters of solar-type stars, requiring further observations to confirm, and theoretical efforts to explain them. Finally, the observed binary properties inform us on the prospects of both finding and RR Lyrae variable in an eclipsing binary system, as well as on the possibility of obtaining an astrometric mass measurement using observations of the Gaia satellite....