Browsing by Author "Hajdu, Gergely"
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- ItemA 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
- ItemA Near-infrared RR Lyrae Census along the Southern Galactic Plane: The Milky Way's Stellar Fossil Brought to Light(2018) Dekany, Istvan; Hajdu, Gergely; Grebel, Eva K.; Catelan, Márcio; Elorrieta López, Felipe; Eyheramendy Duerr, Susana; Majaess, Daniel; Jordán Colzani, Andrés Cristóbal
- ItemContinued 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....
- ItemEstablishing the galactic centre distance using VVV bulge RR lyrae variables(2018) Majaess, D.; Dékány, I.; Hajdu, Gergely; Minniti, D.; Turner, D.; Gieren Waiblinger, Wolfgang Paul
- ItemInto the Darkness: Classical and Type II Cepheids in the Zona Galactica Incognita(2019) Dekany, Istvan; Hajdu, Gergely; Grebel, E.K.; Catelan, Márcio
- ItemMultiple 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, MárcioSince 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....
- ItemMultiwavelength study of the low-luminosity outbursting young star HBC. 722(2016) Kospal, A.; Abraham, P.; Acosta, J.; Dunham, M.; Garcia, D.; Hogerheijde, M.; Kun, M.; Moor, A.; Farkas, A.; Hajdu, Gergely; Kovacs, T.; Kriskovics, L.; Marton, G.; Molnar, L.; Pal, A.; Sarneczky, K.
- ItemNew RR Lyrae variables in binary systems(2015) Hajdu, Gergely; Catelan, Márcio; Dekany, Istvan
- ItemOn the modulation of rr lyrae stars in the globular cluster m3(2014) Jurcsik, J.; Smitola, P.; Hajdu, Gergely; Nuspl, J.
- ItemOn the optimal calibration of VVV photometry(2020) Hajdu, Gergely; Dekany, Istvan; Catelan, Márcio; Grebel, E. K.
- ItemOptical/Near-Infrared Light-Curve Properties of Pulsating Variables in the Cepheid Instability Strip(2014) Calderón Espinoza, Diego Nicolás; Hajdu, Gergely; Dékány, I.; Catelan, MárcioMaking the distinction between Type I and II Cepheids found in the Vista Variables in the Via Lactea (VVV) ESO Public Survey is crucial for the studies of Galactic structure using these variables. As VVV provides only K_{S}-band light curves, this distinction has to be based on near-IR light-curve properties. Because of their reduced amplitudes in the near-IR, however, it is not immediately obvious whether such a distinction can be unambiguously made. To assess this problem, we have compared the VVV and VVV Templates K_{S}-band light-curve properties of 213 Type I and 215 Type II Cepheids using Fourier decomposition. The Fourier parameters of these types were found to be different enough for the purposes of classification. For example, over most of the Cepheid period range, there is an upper limit for the amplitudes of Type I Cepheids. As 50 percent of the Type II variables lie above this limit, half of the variables that could be confused with Type I Cepheids are sorted out by this simple feature alone, suggesting that the automatic classification schemes under development for the VVV Survey will be able to classify such variables with a high degree of accuracy. We have also found that bump Cepheids can be easily identified using VVV data, as the bump feature also appears in the near-IR light curves. Detailed modeling of the light curves of the bump Cepheids found in the VVV data will provide accurate stellar parameters for these stars....
- ItemOvertone and multi-mode RR lyrae stars in the globular cluster M3(2015) Jurcsik, J.; Smitola, P.; Hajdu, Gergely; Sodor, A.; Nuspl, J.; Kolenberg, K.; Furesz, G.; Moor, A.; Kun, E.; Pal, A.; Bakos, J.; Kelemen, J.; Kovacs, T.; Kriskovics, L.; Sarneczky, K.; Szalai, T.; Szing, A.; Vida, K.
- ItemPhotometric and radial-velocity time series of RR Lyrae stars in M3: analysis of single-mode variables(2017) Jurcsik, J.; Smitola, P.; Hajdu, Gergely; Sódor, Á.; Nuspl, J.; Kolenberg, K.; Furész, G.; Balázs, L. G.; Pilachowski, C.; Saha, A.
- ItemProperties 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, IanDespite 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....
- ItemRR Lyrae binary systems in the Galactic bulge(2017) Hajdu, Gergely; Catelan, MarcioThe possibility of a direct mass measurement of RR Lyrae variable stars in binary systems has remained elusive for many years, due to the apparent paucity of such systems. Motivated by our recent success of finding a population of high confidence candidates, we have been continuing the search for RR Lyrae variables in binary systems towards the Galactic bulge. We describe the preliminary results of our project in these proceedings....
- ItemStellar Variability in the VVV Survey: Highlights and Current Status(2015) Catelan, Marcio; Dékány, István; Minniti, Dante; Alonso-Garcia, Javier; Contreras Ramos, Rodrigo; Saito, Roberto; Hajdu, Gergely; Lucas, Phil; Kerins, Eamonn; Hempel, MarenThe Vista Variables in the Via Lactea (VVV) ESO Public Survey consists in a near-infrared time-series survey of the Galactic bulge and inner disk, covering 562 square degrees of the sky, over a total timespan of more than 5 years. In this contribution, we discuss some of our latest results, and provide an updated account of the current status of the survey, especially in the context of stellar variability studies....
- ItemStructure of the obscured galactic disk with pulsating variables.(2019) Hajdu, Gergely; Catelan, Márcio; Pontificia Universidad Católica de Chile. Instituto de AstrofísicaLas estrellas variables pulsantes brillantes, tales como Cefeidas y RR-Lyras, son sondas fundamentales de la estructura de las componentes vieja y joven de la Vía Láctea. Sin embargo, el lado más alejado del disco de la Galaxia aún no ha sido mapeado usando tales variables debido a la severa extinción causada por polvo interestelar en frente de ellas. En esta tesis, las curvas de luz en infrarrojo cercano de la muestra VISTA Variables in the Vía Láctea son utilizadas para penetrar esas regiones y descubrir miles de Cefeidas o RR Lyras previamente “escondidas”. El análisis de las curvas de luz de las variables RR Lyras fue ejecutado con un algoritmo de ajuste, y sus metalicidades determinadas de siluetas de sus curvas de luz en el infrarrojo cercano usando métodos recientemente desarrollados. Estas abundancias fotométricas de metales, con sus posiciones en el disco Galáctico, apoyan las teorílas de la formación de adentro hacia fuera del disco de la Galaxia. Las Cefeidas descubiertas fueron clasificadas en los subtipos viejo (Tipo II) y nuevo (Clásicas). Una nueva ley de extinción en el infrarrojo cercano fue determinada usando Cefeidas Tipo II, utilizando su concentración en el centro Galáctico. La distribución de las Cefeidas Clásicas en el disco Galáctico sigue el pandeo Galáctico y el ensanchamiento del disco de la Galaxia en grandes radios Galactocéntricos. Un primer intento se efectuó con el fin de conectar las ubicaciones actuales de las Cefeidas Clásicas con la estructura de brazos espirales de la Vía Láctea.
- ItemThe Hidden Potential of VVV RR Lyrae Light Curves(2018) Hajdu, Gergely; Catelan, Marcio; Dékány, István; Grebel, Eva K.We introduce a new method of determining the average magnitudes of RR Lyrae variables: in the K_{S}-band, based on robust fitting of principal components from a high-quality training sample; in the J-band, using the amplitudes of the K_{S} principal components to approximate the J-band light-curve shape in each pulsation phase. Furthermore, it has been found that the metallicity of individual RR Lyrae variables can be inferred from the K_{S}-band light curves....
- ItemThe MAGIC project - II. Discovery of two new Galactic lithium-rich Cepheids(2019) Kovtyukh, V.; Lemasle, B.; Kniazev, A.; Berdnikov, L.; Bono, G.; Usenko, I.; Grebel, E. K.; Hajdu, Gergely; Pastukhova, E.