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Register a new userAn extensive photometric study of the Blazhko RR Lyrae star DM Cyg
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DM Cyg, a fundamental mode RRab star was observed in the 2007 and 2008 seasons in the frame of the Konkoly Blazhko Survey. Very small amplitude light curve modulation was detected with 10.57 d modulation period. The maximum brightness and phase variations do not exceed 0.07 mag and 7 min, respectively. In spite of the very small amplitude of the modulation, beside the frequency triplets characterizing the Fourier spectrum of the light curve two quintuplet components were also identified. The accuracy and the good phase coverage of our observations made it possible to analyse the light curves at different phases of the modulation separately. Utilizing the IP method (Sodor, Jurcsik and Szeidl, 2009) we could detect very small systematic changes in the global mean physical parameters of DM Cyg during its Blazhko cycle. The detected changes are similar to what we have already found for a large modulation amplitude Blazhko variable MW Lyrae. The amplitudes of the detected changes in the physical parameters of DM Cyg are only about 10% of that what have been found in MW Lyr. This is in accordance with its small modulation amplitude being about one tenth of the modulation amplitude of MW Lyr.
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We have obtained the most extensive and most accurate photometric data of a Blazhko variable MW Lyr during the 2006-2007 observing seasons. The data within each 0.05 phase bin of the modulation period (P_m=1/f_m) cover the entire light cycle of the primary pulsation period (P_0=1/f_0), making possible a very rigorous and complete analysis. The modulation period is found to be 16.5462 d, which is about half of that was reported earlier from visual observations. Previously unknown features of the modulation have been detected. Besides the main modulation frequency f_m, sidelobe modulation frequencies around the pulsation frequency and its harmonics appear at +/- 2 f_m, +/- 4 f_m, and +/- 12.5 f_m separations as well. Residual signals in the prewhitened light curve larger than the observational noise appear at the minimum-rising branch-maximum phase of the pulsation, which most probably arise from some stochastic/chaotic behaviour of the pulsation/modulation. The Fourier parameters of the mean light curve differ significantly from the averages of the Fourier parameters of the observed light curves in the different phases of the Blazhko cycle. Consequently, the mean light curve of MW Lyrae never matches its actual light variation. The Phi_21, Phi_31 phase differences in different phases of the modulation show unexpected stability during the Blazhko cycle. A new phenomenological description of the light curve variation is defined that separates the amplitude and phase (period) modulations utilising the phase coherency of the lower order Fourier phases.
The Blazhko effect is the conspicuous amplitude and phase modulation of the pulsation of RR Lyrae stars that was discovered in the early 20th century. The field of study of this mysterious modulation has recently been invigorated thanks to the space photometric missions providing long, uninterrupted, ultra-precise time series data. In this paper I give a brief overview of the new observational findings related to the Blazhko effect, like extreme modulations, irregular modulation cycles and additional periodicities. I argue that these findings together with dedicated ground-based efforts now provide us with a fairly complete picture and a good starting point to theoretical investigations. Indeed, new, unpredicted dynamical phenomena have been discovered in Blazhko RR Lyrae stars, such as period doubling, high-order resonances, three-mode pulsation and low-dimensional chaos. These led to the proposal of a new explanation to this century-old enigma, namely a high-order resonance between radial modes. Along these lines I present the latest efforts and advances from the theoretical point of view. Lastly, amplitude variations in Cepheids are discussed.
We present the results of a photometry campaign of TU Com performed over a five-year time span. The analysis showed that the possible Blazhko period of 75 days published by the General Catalogue of Variable Stars is not correct. We identified two Blazhko periods of 43.6 and 45.5 days. This finding is based on measurement of 124 light maxima. A spectral analysis of the complete light curve confirmed these two periods. Besides the Blazhko amplitude and phase modulations, another long term periodic phase variation has been identified. This long term periodic variation affects the times of maximum light only and can be attributed to a light-travel time effect due to orbital motion of a binary system. The orbital parameters have been estimated by a nonlinear least-square fit applied to the set of (O-C) values. The Levenberg-Marquart algorithm has been used to perform the nonlinear least-square fit. The tentative orbital parameters include an orbital period of 1676 days, a minimal semi-major axis of 1.55 AU and a small eccentricity of 0.22. The orbital parameter estimation also used 33 (O-C) values obtained from the SWASP survey database. Spectroscopic radial velocity measurements are needed to confirm this binarity. If confirmed, TU Com would be the first Blazhko RR Lyrae star detected in a binary system.
This paper summarizes the main results of our recent study of the non-Blazhko RR Lyrae stars observed with the Kepler space telescope. These stars offer the opportunity for studying the stability of the pulsations of RR Lyrae stars and for providing a reference against which the Blazhko RR Lyrae stars can be compared. Of particular interest is the stability of the low-dispersion (sigma < 1mmag) light curves constructed from ~18,000 long-cadence (30-min) and (for FN Lyr and AW Dra) the ~150,000 short-cadence (1-min) photometric data points. Fourier-based [Fe/H] values and other physical characteristics are also derived. When the observed periods are compared with periods computed with the Warsaw non-linear convective pulsation code better agreement is achieved assuming pulsational L and M values rather than the (higher) evolutionary L and M values.
The results presented are a continuation of observing campaigns conducted by a small group of amateur astronomers interested in the Blazhko effect of RR Lyrae stars. The goal of these observations is to confirm the RR Lyrae Blazhko effect and to detect any additional Blazhko modulation which cannot be identified from all sky survey data-mining. The Blazhko effect of the two observed stars is confirmed, but no additional Blazhko modulations have been detected. The observation of the RR Lyrae star AL Pic during 169 nights was conducted from San Pedro de Atacama (Chile). From the observed light curve, 49 pulsation maxima have been measured. Fourier analyses of (O-C), magnitude at maximum light (Mmax) and the complete light curve have provided a confirmation of published pulsation and Blazhko periods, 0.548622 and 34.07 days, respectively. The second multi-longitude observation campaign focused on the RR Lyrae star FR Psc was performed from Europe, United States and Chile. Fourier analyses of the light curve and of 59 measured brightness maxima have improved the accuracy of pulsation and Blazhko periods which are 0.45568 and 51.31 days, respectively. For both stars, no additional Blazhko modulations have been detected.
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