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Öğe A Comprehensive Study of the Eclipsing Binaries V1241 Tau and GQ Dra(Copernicus Foundation Polish Astronomy, 2020) Ulas, B.; Gazeas, K.; Liakos, A.; Ulusoy, C.; Stateva, I; Erkan, N.; Napetova, M.We present new photometric and spectroscopic observations and analyses for the eclipsing binary systems V1241 Tau and GQ Dra. Our photometric light and radial velocity curve analyses combined with the TESS light curves show that both are conventional semi-detached binary systems. Their absolute parameters are also derived. We present the O-C analyses of the systems and we propose the most likely orbital period modulating mechanisms. Furthermore, Fourier analyses are applied to the photometric residual data of the systems to check for the pulsational behavior of the components. We conclude that the primary component of the system GQ Dra is a delta Set type pulsator with a dominant pulsation frequency of 18.58 d(-1) based on our B filter residual light curve although it cannot be verified by 30-minute cadence TESS data. No satisfactory evidence of pulsational behavior for V1241 Tau was verified. Finally, the evolutionary tracks of the components of both systems are calculated. Their locations within evolutionary diagrams are compared with other Algol-type systems.Öğe A multiwavelength study of the M dwarf binary YY Geminorum(Oxford Univ Press, 2015) Butler, C. J.; Erkan, N.; Budding, E.; Doyle, J. G.; Foing, B.; Bromage, G. E.; Kellett, B. J.We review the results of the 1988 multiwavelength campaign on the late-type eclipsing binary YY Geminorum. Observations include: broad-band optical and near-infrared photometry, simultaneous optical and ultraviolet (IUE) spectroscopy, X-ray (Ginga) and radio (VLA) data. From models fitted to the optical light curves, fundamental physical parameters have been determined together with evidence for transient maculations (spots) located near quadrature longitudes and intermediate latitudes. Eclipses were observed at optical, ultraviolet and radio wavelengths. Significant drops in 6 cm radio emission near the phases of both primary and secondary eclipse indicate relatively compact radio emitting volumes that may lie between the binary components. IUE observations during secondary eclipse are indicative of a uniform chromosphere saturated with Mg II emission and an extended volume of Ly alpha emission. Profile fitting of high-dispersion Ha spectra confirms the chromospheric saturation and indicates significant Ha opacity to heights of a few per cent of the photospheric radius. There is evidence for an enhanced Ha emission region visible near phase 0.25-0.35 which may be associated with a large spot on the primary and with two small optical flares which were also observed at other wavelengths: one in microwave radiation and the other in X-rays. For both flares, L-X/L-opt is consistent with energy release in closed magnetic structures.Öğe Cool Active Binaries Recently Studied in the CAAM Stellar Program(Astronomical Soc Pacific, 2010) Cicek, C.; Erdem, A.; Soydugan, Faruk; Dogru, D.; Ozkardes, B.; Erkan, N.; Budding, E.We summarize recent work on cool active stars in our programme. We carried out photometry at the canakkale Onsekiz Mart University (COMU) observatory, and high-resolution spectroscopy at Mt John University Observatory, as well as collecting data from other facilties. A combination of analysis methods, including our information limit optimization technique (ILOT) with physically realistic fitting functions, as well as other public-domain software packages, have been used to find reliable parameters. Stars in our recent programme include V1430 Aql, VI 034 Her, V340 Gem, SAO 62042, FI Cnc, V2075 Cyg, FG UMa and BM CVn. Light variations, sometimes over numerous consecutive cycles, were analysed. For AB Dor and CF Tuc, we compared broadband (B and V) maculation effects with emission features in the Ca II K and H-alpha lines. Broadband light curves typically show one or two outstanding maculae. These appear correlated with the main chromospheric activity sites ('faculae'), that occur at similar latitudes and with comparable size to the photometric umbrae, but sometimes with significant displacements in longitude. The possibility of large-scale bipolar surface structure is considered, keeping in mind solar analogies. Such optical work forms part of broader multiwavelength studies, involving X-ray and microwave observations, also mentioned.Öğe Multisite, multiwavelength studies of the active cool binary CC Eri(2006) Budding, E.; Bembrick, C.; Carter, B.D.; Erkan, N.; Jardine, M.; Marsden, S.C.; Osten, R.New data acquired on the active, cool binary CC Eri ranged across the spectrum from Chandra X-ray to broadband photometry and microwave observations using the VLA and ATCA. Also, high-dispersion spectropolarimetry using the AAT enabled Zeeman-Doppler imaging to be performed. Our interpretations infer strong localised concentrations of the stellar magnetic field, manifested by surface activity and related large coronal plasma structures. Comprehensive matching of the modelling parameters awaits more detailed investigation. This brief interim review includes consideration of the ATCA data. Microwave radio emission is usually low level ('quiescent'), but occasionally flares of several mJy peak intensity are observed. We associate the emission, generally, with wave-like mechanisms, expanding through the outer atmosphere. Related characteristics of this emission are discussed. © Springer Science+Business Media B.V. 2006.Öğe Multiwavelength Observations of AB Doradus(Cambridge Univ Press, 2014) Slee, O. B.; Erkan, N.; Johnston-Hollitt, M.; Budding, E.We have observed the bright, magnetically active multiple star AB Doradus in a multiwavelength campaign centring around two large facility allocations in November 2006 and January, 2007. Our observations have covered at least three large flares. These flares were observed to produce significant hardening of the X-ray spectra during their very initial stages. We monitored flare-related effects using the Suzaku X-ray satellite and the Australia Telescope Compact Array (ATCA) at 3.6 and 6 cm. Observations at 11 and 21 cm were also included, but they were compromised by interference. Optical monitoring was also provided by broadband B and V photometry and some high-dispersion spectrograms. From this multiwavelength coverage we find that the observed flare effects can be mainly associated with a large active region near longitude zero. The second major X-ray and microwave flare of Jan 8, 2007 was observed with a favourable geometry that allowed its initial high-energy impulsive phase to be observed in the higher frequency range of Suzaku's XIS detectors. The fractional circular polarisation (Stokes V/I) was measured in the uv data for the complete runs, for 25 min integrations and, at 4.80 GHz, for 5 min integrations, using the radio data of Nov 21 2006 and Jan 08 2007. Most of the full data sets showed V/I fractions from AB Dor B that were significant at greater than the 3 sigma level. In several of the 5 min integrations at 4.80 and 8.64 GHz this fraction reached a significance level between 3 and 9 sigma. Lack of angular resolution prevented identification of these high V/I values with one or other of the two low-mass red-dwarf components of AB Dor B.Öğe The low mass ratio contact binary system V728 Herculis(Elsevier Science Bv, 2016) Erkan, N.; Ulas, B.We present the orbital period study and the photometric analysis of the contact binary system V728 Her. Our orbital period analysis shows that the period of the system increases (dP/dt = 1.92 x 10(-7)dyr(-1)) and the mass transfer rate from the less massive component to more massive one is 2.51 x 10(-8) M(circle dot)y(-1). In addition, an advanced sinusoidal variation in period can be attributed to the light-time effect by a tertiary component or the Applegate mechanism triggered by the secondary component. The simultaneous multicolor BVR light and radial velocity curves solution indicates that the physical parameters of the system are M-1 = 1.8M(circle dot), M-2 = 0.28M(circle dot), R-1 = 1.87R(circle dot), R-2 = 0.82R(circle dot), L-1 = 5.9L(circle dot), and L-2 = 1.2L(circle dot). We discuss the evolutionary status and conclude that V728 Her is a deep (f = 81%), low mass ratio (q = 0.16) contact binary system. (C) 2015 Elsevier B.V. All rights reserved.
