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Borkovits T.,Baja Astronomical Observatory | Paragi Z.,Joint Institute for VLBI in Europe | Paragi Z.,MTA Research Group for Physical Geodesy and Geodynamics | Csizmadia S.,German Aerospace Center
Journal of Physics: Conference Series | Year: 2010

Both theoretical and indirect observational evidences suggest that most of the closest binary stars with orbital periods of few days (as well as hot Jupiter-type exoplanets) formed with an original separation larger by 1-2 orders of magnitude than the present one. Consequently, an orbital shrinking mechanism(s) must be present that extracts the angular momentum from a primordial binary. From the possible mechanisms studied in the literature we describe the so-called 'Kozai cycles combined with tidal friction' (KCTF), which gives some definite predictions for the statistical properties of the orbital elements in such close binaries. Due to the recent powerful observing techniques, such as optical and radio (VLBI) interferometry, we can already peer inside such close binaries, so we have some opportunity to check these predictions. We examine the practical details, constraints, restrictions about the inquiring of the necessary information from specific triple systems by interferometric (as well as polarimetric) observations. Finally, to illustrate this we give a brief description of our recent combined optical and radio interferometric measurements of Algol. © 2010 IOP Publishing Ltd.

Olah K.,Konkoly Observatory MTA CsFK | Moor A.,Konkoly Observatory MTA CsFK | Strassmeier K.G.,Leibniz Institute for Astrophysics Potsdam | Borkovits T.,Konkoly Observatory MTA CsFK | And 3 more authors.
Astronomische Nachrichten | Year: 2013

We present and analyze long-term optical photometric measurements of the three active stars V2253 Oph, IT Com and IS Vir. All three systems are single-lined spectroscopic binaries with an early K giant as primary component but in different stages of orbital-rotational synchronization. Our photometry is supplemented by 2MASS and WISE near-IR and mid-IR magnitudes and then used to obtain more accurate effective temperatures and extinctions. For V2253 Oph and IT Com, we found their spectral energy distributions consistent with pure photospheric emission. For IS Vir, we detect a marginal mid-IR excess which hints towards a dust disk. The orbital and rotational planes of IT Com appear tobe coplanar, contrary to previous findings in the literature. We apply a multiple frequency analysis technique to determine photometric periods, and possibly changes of periods, ranging from days to decades. New rotational periods of 21.55±0.03 d, 65.1±0.3 d, and 23.50±0.04 d were determined for V2253 Oph, IT Com, and IS Vir, respectively. Splitting of these periods led to tentative detections of differential surface rotations of δP/P ≈ 0.02 for V2253 Oph and 0.07 for IT Com. Using a time-frequency technique based on short-term Fourier transforms we present evidence of cyclic light variations of length ≈ 10 yr for V2253 Oph and 5-6 yr for IS Vir. A single flip-flop event has been observed for IT Com of duration 2-3 yr. Its exchange of the dominant active longitude had happened close to a time of periastron passage, suggesting some response of the magnetic activity from the orbital dynamics. The 21.55-d rotational modulation of V2253 Oph showed phase coherence also with the orbital period, which is 15 times longer than the rotational period, thus also indicating a tidal feedback with the stellar magnetic activity. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tran K.,Kavli Institute for Astrophysics and Space Research | Levine A.,37 575 Mit Kavli Institute For Astrophysics And Space Research | Rappaport S.,Kavli Institute for Astrophysics and Space Research | Borkovits T.,Baja Astronomical Observatory | And 5 more authors.
Astrophysical Journal | Year: 2013

We report a study of the eclipse timing variations in contact binary systems, using long-cadence lightcurves from the Kepler archive. As a first step, observed minus calculated (O-C) curves were produced for both the primary and secondary eclipses of some 2000 Kepler binaries. We find ∼390 short-period binaries with O-C curves that exhibit (1) random walk-like variations or quasi-periodicities, with typical amplitudes of ±200-300 s, and (2) anticorrelations between the primary and secondary eclipse timing variations. We present a detailed analysis and results for 32 of these binaries with orbital periods in the range of 0.35 ± 0.05 days. The anticorrelations observed in their O-C curves cannot be explained by a model involving mass transfer, which, among other things, requires implausibly high rates of ∼0.01 MȮ yr-1. We show that the anticorrelated behavior, the amplitude of the O-C delays, and the overall random walk-like behavior can be explained by the presence of a starspot that is continuously visible around the orbit and slowly changes its longitude on timescales of weeks to months. The quasi-periods of ∼50-200 days observed in the O-C curves suggest values for k, the coefficient of the latitude dependence of the stellar differential rotation, of ∼0.003-0.013. © 2013. The American Astronomical Society. All rights reserved.

Vinko J.,University of Szeged | Vinko J.,University of Texas at Austin | Sarneczky K.,Konkoly Observatory | Sarneczky K.,ELTE Gothard Lendulet Research Group | And 23 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. The nearby, bright, almost completely unreddened Type Ia supernova 2011fe in M101 provides a unique opportunity to test both the precision and the accuracy of the extragalactic distances derived from SNe Ia light curve fitters. Methods. We applied the current, public versions of the independent light curve fitting codes MLCS2k2 and SALT2 to compute the distance modulus of SN 2011fe from high-precision, multi-color (BVRI) light curves. Results. The results from the two fitting codes confirm that 2011fe is a "normal" (not peculiar) and only slightly reddened SN Ia. New unreddened distance moduli are derived as 29.21 ± 0.07 mag (D ~ 6.95 ± 0.23 Mpc, MLCS2k2), and 29.05 ± 0.07 mag (6.46 ± 0.21 Mpc). Conclusions. Despite the very good fitting quality achieved with both light curve fitters, the resulting distance moduli are inconsistent by 2σ. Both are marginally consistent (at ~1σ) with the Hubble Space Telescope key project distance modulus for M101. The SALT2 distance is in good agreement with the recently revised Cepheid-and TRGB-distance to M101. Averaging all SN-and Cepheid-based estimates, the absolute distance to M101 is ~6.6 ± 0.5 Mpc. ©2012 ESO.

Borkovits T.,Baja Astronomical Observatory | Borkovits T.,Konkoly Observatory | Borkovits T.,ELTE Gothard Lendulet Research Group | Derekas A.,Konkoly Observatory | And 14 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

HD 181068 is the brighter of the two known triply eclipsing hierarchical triple stars in the Kepler field. It has been continuously observed for more than 2 yr with the Kepler space telescope. Of the nine quarters of the data, three have been obtained in short-cadence mode, that is one point per 58.9 s. Here we analyse this unique data set to determine absolute physical parameters (most importantly the masses and radii) and full orbital configuration using a sophisticated novel approach. We measure eclipse timing variations (ETVs), which are then combined with the single-lined radial velocity measurements to yield masses in a manner equivalent to double-lined spectroscopic binaries. We have also developed a new light-curve synthesis code that is used to model the triple, mutual eclipses and the effects of the changing tidal field on the stellar surface and the relativistic Doppler beaming. By combining the stellar masses from the ETV study with the simultaneous light-curve analysis we determine the absolute radii of the three stars. Our results indicate that the close and the wide subsystems revolve in almost exactly coplanar and prograde orbits. The newly determined parameters draw a consistent picture of the system with such details that have been beyond reach before. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Fuller J.,Cornell University | Derekas A.,Hungarian Academy of Sciences | Derekas A.,University of Sydney | Borkovits T.,Hungarian Academy of Sciences | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate the nature of tidal effects in compact triple-star systems. The hierarchical structure of a triple system produces tidal forcing at high frequencies unobtainable in binary systems, allowing for the tidal excitation of high-frequency p-modes in the stellar components. The tidal forcing exists even for circular, aligned and synchronized systems. We calculate the magnitude and frequencies of three-body tidal forcing on the central primary star for circular and coplanar orbits, and we estimate the amplitude of the tidally excited oscillation modes.We also calculate the secular orbital changes induced by the tidally excited modes and show that they can cause significant orbital decay. During certain phases of stellar evolution, the tidal dissipation may be greatly enhanced by resonance locking. We then compare our theory to observations of HD 181068, which is a hierarchical triply eclipsing star system in the Kepler field of view. The observed oscillation frequencies in HD 181068 can be naturally explained by three-body tidal effects. We then compare the observed oscillation amplitudes and phases in HD 181068 to our predictions, finding mostly good agreement. Finally, we discuss the past and future evolution of compact triple systems like HD 181068. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Rappaport S.,Kavli Institute for Astrophysics and Space Research | Deck K.,Kavli Institute for Astrophysics and Space Research | Levine A.,37 575 Mit Kavli Institute For Astrophysics And Space Research | Borkovits T.,Baja Astronomical Observatory | And 7 more authors.
Astrophysical Journal | Year: 2013

We present the results of a search through the photometric database of Kepler eclipsing binaries looking for evidence of hierarchical triple-star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O-C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ∼1/2 hr Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O-C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called physical delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O-C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple-star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions. © 2013. The American Astronomical Society. All rights reserved..

Kovacs J.,University of Pécs | Sajo I.,University of Pécs | Marton Z.,MTA PTE High Field Terahertz Research Group | Marton Z.,University of Pécs | And 6 more authors.
Planetary and Space Science | Year: 2015

We report here for the first time the composition and mineralogical studies on a new meteorite, which was found in August 2012 near the village of Csátalja, Hungary (46°0'21-N; 18°59'27'E). The Csátalja meteorite is classified as a H4-5 ordinary chondrite with shock stage S2 and a degree of weathering W1 and the total mass is 15 kg. The Csátalja meteorite is characterized by well-defined chondrules composed either of olivine or pyroxene. X-ray diffractogram shows the primary phases olivine, pyroxene, kamacite, and albite. Metal particles were extracted from the bulk powdered samples exhibit only kamacite and small amounts of the intergrowth taenite/kamacite. Raman spectra of forsterite indicate that Csátalja meteorite suffered from relatively low shock pressure regime. The texture of chondrules varies from nonporphyritic (e.g., barred olivine, radial pyroxene) to porphyritic ones (e.g., granular olivine as well as olivine pyroxene). The meteorite name has not yet approved by the Nomenclature Committee of the Meteoritical Society. © 2014 Elsevier Ltd. All rights reserved.

Szabados L.,Hungarian Academy of Sciences | Cseh B.,ELTE Gothard Lendulet Research Group | Cseh B.,Eötvös Loránd University | Kovacs J.,ELTE Gothard Lendulet Research Group | And 14 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present the analysis of photometric and spectroscopic data of two classical Cepheids, FN Aquilae and V1344 Aquilae. Based on the joint treatment of the new and earlier radial velocity data, both Galactic Cepheids have been found to be a member in a spectroscopic binary system. To match the phases of the earlier radial velocity data correctly with the new ones, we also determined the temporal behaviour of the pulsation period of these Cepheids based on all available photometric data. The O - C graph covering about half century shows slight changes in the pulsation period due to stellar evolution for both Cepheids. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Biro I.B.,Baja Astronomical Observatory | Nuspl J.,Hungarian Academy of Sciences
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present the dynamic eclipse mapping method designed specifically to reconstruct the surface intensity patterns of non-radial stellar oscillations on components of eclipsing binaries. The method needs a geometric model of the binary, accepts the light curve and the detected pulsation frequencies on input, and on output yields estimates of the pulsation patterns, in the form of images, thus allowing a direct identification of the surface mode numbers (ℓ, m). Since it has minimal modelling requirements and can operate on photometric observations in arbitrary wavelength bands, dynamic eclipse mapping is well suited to analyse the wide-band time series collected by space observatories. We have investigated the performance and the limitations of the method through extensive numerical tests on simulated data, in which almost all photometrically detectable modes with a latitudinal complexity ℓ- |m| ≤ 4 were properly restored. The method is able by its nature to simultaneously reconstruct multimode pulsations from data covering a sufficient number of eclipses as well as pulsations on components with a tilted rotation axis of a known direction. It can also be applied in principle to isolate the contribution of hidden modes from the light curve. Sensitivity tests show that moderate errors in the geometric parameters and the assumed limb darkening can be partially tolerated by the inversion, in the sense that the lower degree modes are still recoverable. Tidally induced or mutually resonant pulsations, however, are an obstacle that neither the eclipse mapping nor any other inversion technique can ever surpass. We conclude that, with reasonable assumptions, dynamic eclipse mapping could be a powerful tool for mode identification, especially in moderately close eclipsing binary systems, where the pulsating component is not seriously affected by tidal interactions so that the pulsations are intrinsic to them, and not a consequence of the binarity. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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