Shockwave Behaviour in RR Lyrae Stars

Here we present the detailed analysis of some modulated Kepler and K2 RR Lyrae stars that show peculiar bump progression in respect to the pulsation phase.Comment: 3 pages, 3 figures, to be published in the proceedings of "The RR Lyrae 2017 Conference", Niepolomice, Poland, 17-21 September 201

Classification of OGLE Eclipsing Binary Stars Based on Their Morphology Type with Locally Linear Embedding

The Optical Gravitational Lensing Experiment (OGLE) continuously monitors hundreds of thousands of eclipsing binaries in the Galactic bulge field and the Magellanic Clouds. These objects have been classified into major morphological subclasses, such as contact, noncontact, ellipsoidal, and cataclysmic variables, both by matching the light curves with predefined templates and by visual inspections. Here we present the result of a machine-learned automatic classification based on the morphology of light curves inspired by the classification of eclipsing binaries observed by the original Kepler mission. We similarly use a dimensionality reduction technique with locally linear embedding to map the high dimension of the data set into a low-dimensional embedding parameter space, while keeping the local geometry and the similarities of the neighboring data points. After three consecutive steps, we assign one parameter to each binary star, which scales well with the "detachness," i.e., the sum of the relative radii of the components. This value is in good agreement with the morphology types listed in the OGLE catalog and, along with the orbital periods, can be used to filter any morphological subtypes based on the similarity of light curves. Our open-source pipeline can be applied in a fully automatic way to any other large data set to classify binary stars

Csoportgyűrűk és keresztszorzatok = Group rings and crossed products

Jelen pályázat fő eredményei az FG csoportalgebra Lie srtuktúrájának és a normalizált V(FG) egységcsoportjának leírása egyes esetekben, továbbá FG filtrációs bázisának létezése és az általános kristálycsoport vizsgálata. Jellemeztük a maximális és majdnem maximális indexű Lie nilpotens csoportalgebrát. Ha G véges p-csoport, akkor a V(FG) konjugált osztályainak rendjét és hatványteljes struktúráját vizsgáltuk, továbbá azt, hogy mikor teljesül Berman sejtése, azaz, a V(FG) mikor határozza meg egyértelműen a G csoportot. Kiterjesztettük kutatásainkat a csoportazonosságok vizsgálatára a V(FG)-n és megoldást nyert két nagyon nehéz probléma: az FG jellemzése korlátos Engel, illetve feloldható egységcsoporttal. Folytattuk a vizsgálatokat az FG filtrációs bázisának létezéséről, megmutattuk, hogy ha G nem kommutatív hatványteljes, akkor FG-nek nincsen filtrációs bázisa. Sikerült a filtrációs bázis leírása abban az esetben, ha G-nek van p^2 indexű ciklikus részcsoportja. A reprezentáció elméleti kutatásokat kiterjesztettük az általános kristálycsoportokra és az elért eredmények alapján új struktúra tételeket kaptunk a klasszikus kristálycsoportra. A kutatások egy részét az argentin Cordoba-i egyetem munkatársaival közösen végeztük és tovább folytatjuk egy nemzetközi pályázat keretében. Elkészítettük és publikáltuk a LAGUNA programcsomagot, amely segítségével az FG-ben és V(FG)-ben végezhetünk vizsgálatokat számítógéppel. E programcsomag felhasználásával sikerült igazolni, hogy a 3 dimenziós kristálycsoportok holonómia csoportjaira a Zassenhaus első sejtése érvényes. | The main results of our work are the description of the Lie structure and the normalized group of units V(FG) of the group algebra FG in certain cases and the investigation of the existence of filtered bases of FG. We studied the generalized crystallographic groups. We described the group algebras with maximal and "almost maximal" Lie nilpotency indices. Furthermore, we studied the order of conjugacy classes and the powerful structure of V(FG) in the case when G is a finite p-group, and we investigated a famous conjecture of Berman, namely, when does V(FG) determine the group G. We extended our research to the study of group identities on V(FG) and solved the following two difficult problems: we described the group algebras (i) which are bounded Engel; (ii) whose group of units is solvable. We continued the study of the existence of filtered bases of FG and showed that if G is non-commutative and powerful, then G has no filtered bases. We described the filtered bases when G has a cyclic subgroup of index p^2. Using the theory of the integral representation of finite groups, we studied the generalized crystallographic groups, and we applied the above results to give new structure theorems on the classical crystallographic groups. Some parts of these results were obtained jointly with researchers from the University of Cordoba. We developed the computer algebraic system LAGUNA, which is an useful tool to investigate FG and V(FG). By the help of LAGUNA we proved the first conjecture of Zassenhaus for the holonomy group of crystallographic groups of dimension 3

Testing Ultra-low Amplitude Cepheid Candidates in the Galactic Disk by TESS and Gaia

Ultra-low amplitude (ULA) and strange mode Cepheids are thought to be pulsating variable stars that are near to or are at the edges of the classical instability strip. Until now, a few dozen such variable star candidates have been found both in the Large Magellanic Cloud and the Milky Way. In this present work, we studied six ULA Cepheid candidates in the Milky Way, identified by Szab\'o et al. (2009) using CoRoT and 2MASS data. In order to identify their positions in the period--luminosity and color--magnitude diagrams, we used the Gaia DR3 parallax and brightness data of each star to calculate their reddening-free absolute magnitudes and distances. Furthermore, we calculated the Fourier parameters (e.g., period and amplitude) of the light variations based on CoRoT and TESS measurements, and established the long-term phase shifts for four out of six stars. Based on the results, we conclude that none of the six ULA Cepheid candidates are pulsating variable stars, but rather rotation-induced variable stars (rotational spotted and $\alpha^2$~Canum Venaticorum variables) that are either bluer or fainter than Cepheids would be.Comment: 14 pages, 6 tables, 10 figures. Accepted to Astronomy and Astrophysic

Physical Properties of Galactic RV Tauri Stars from Gaia DR2 Data

We present the first period–luminosity and period–radius relation of Galactic RV Tauri variable stars. We have surveyed the literature for all variable stars belonging to this class and compiled the full set of their photometric and spectroscopic measurements. We crossmatched the final list of stars with the Gaia Data Release 2 database and took the parallaxes, G-band magnitudes, and effective temperatures to calculate the distances, luminosities, and radii using a probabilistic approach. As it turned out, the sample was very contaminated, and thus we restricted our study to those objects for which the RV Tau nature was securely confirmed. We found that several stars are located outside the red edge of the classical instability strip, which implies a wider pulsational region for RV Tau stars. The period–luminosity relation of galactic RV Tauri stars is steeper than that of the shorter-period Type II Cepheids, in agreement with previous results obtained for the Magellanic Clouds and globular clusters. The median masses of RVa and RVb stars were calculated to be 0.45–0.52 M ⊙ and 0.83 M ⊙, respectively

Automated Extended Aperture Photometry for K2 RR Lyrae stars

Light curves for RR Lyrae stars can be difficult to obtain properly in the K2 mission due to the similarities between the timescales of the observed physical phenomena and the instrumental signals appearing in the data. We developed a new photometric method called Extended Aperture Photometry (EAP), a key element of which is to extend the aperture to an optimal size to compensate for the motion of the telescope and to collect all available flux from the star before applying further corrections. We determined the extended apertures for individual stars by hand so far. Now we managed to automate the pipeline that we intend to use for the nearly four thousand RR Lyrae targets observed in the K2 mission. We present the outline of our pipeline and make some comparisons to other photometric solutions.Comment: To appear in Astronomical Society of the Pacific Conference Series, Volume 529, "RRLyrae/Cepheid2019: Frontiers of Classical Pulsators: Theory and Observations", Cloudcroft, NM, USA October 13-18, 201