A. Szing

An extensive photometric study of the Blazhko RR Lyrae star MW Lyr – I. Light-curve solution

We have obtained the most extensive and most accurate photometric data of a Blazhko variable MWLyrae (MWLyr) during the 2006-2007 observing seasons. The data within each 0.05 phase bin of the modulation period (P m = f -1 m ) cover the entire light cycle of the primary pulsation period (P 0 = f -1 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 ±2f m , ±4f m and ±12.5f m separations as well. Residual signals in the pre-whitened 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 Lyr never matches its actual light variation. The Φ 21 , Φ 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 utilizing the phase coherency of the lower order Fourier phases.

An extensive photometric study of the Blazhko RR Lyrae star MW Lyr – II. Changes in the physical parameters★

The analysis of the multicolour photometric observations of MW Lyr, a large modulation amplitude Blazhko variable, shows for the first time how the mean global physical parameters vary during the Blazhko cycle. About 1-2 per cent changes in the mean radius, luminosity and surface effective temperature are detected. The mean radius and temperature changes are in good accordance with pulsation model results, which show that these parameters do indeed vary within this order of magnitude if the amplitude of the pulsation changes significantly. We interpret the phase modulation of the pulsation to be a consequence of period changes. Its magnitude corresponds exactly what one expects from the detected changes of the mean radius assuming that the pulsation constant remains the same during the modulation. Our results indicate that during the modulation the pulsation remains purely radial, and the underlying mechanism is most probably a periodic perturbation of the stellar luminosity with the modulation period.

The Shortest Modulation Period Blazhko RR Lyrae Star: SS Cancri

Extended BV(RI)C CCD observations of SS Cnc, a short-period RRab star, are presented. Nearly 1400 data points in each band have been obtained, spanning over 79 days during the spring of 2005. The star exhibits light-curve modulation, the so-called Blazhko effect, with small amplitude (B maximum brightness varies by 0.1 mag) and with the shortest modulation period (5.309 days) ever observed. In the Fourier spectrum of the V light curve, the pulsation frequency components are detected up to the 24th harmonic order, and modulation sidelobe frequencies with significantly asymmetric amplitudes are seen up to the 15th and 9th orders for the lower and higher frequency components, respectively. A detailed comparison of the modulation behavior of SS Cnc and RR Gem, two recently discovered small-amplitude, short-modulation-period Blazhko stars, is presented. The modulation frequency (fm) appears in the Fourier spectrum of both stars with similar amplitude. We also demonstrate that the modulation frequencies have basically different properties from those of the pulsation and modulation sidelobe frequencies, indicating that the physics behind these frequency components is not the same. The discovery of small amplitude modulations of RRab stars cautions that the large photometric surveys (MACHO and OGLE) may seriously underestimate the number of modulated RR Lyrae stars.

Pulsational and evolutionary analysis of the double‐mode RR Lyrae star BS Com

ABSTRACT We derive the basic physical parameters of the field double-mode RR Lyrae starBSCom from its observed periods and the requirement of consistency between thepulsational and evolutionary constraints. By using the current solar-scaled horizontalbranch evolutionary models of Pietrinferni et al. (2004) and our linear non-adiabaticpurely radiative pulsational models, we get M/M ⊙ = 0.698 ± 0.004, log(L/L ⊙ ) =1.712±0.005, T eff = 6840±14K, [Fe/H]=−1.67±0.01, where the errors are standarddeviations assuming uniform age distribution along the full range of uncertainty inage. The last two parameters are in a good agreement with the ones derived fromthe observed BVI C colours and the updated ATLAS9 stellar atmosphere models. Weget T eff = 6842 ± 10K, [Fe/H]=−1.58 ± 0.11, where the errors are purely statisticalones. It is remarkable that the derived parameters are nearly independent of stellarage at early evolutionary stages. Later stages, corresponding to the evolution towardthe asymptotic giant branch are most probably excluded because the required hightemperatures are less likely to satisfy the constraints posed by the colours. We alsoshow that our conclusions are only weakly sensitive to nonlinear period shifts predictedby current hydrodynamical models.Key words: stars: individual: BSCom – stars: variables: RR Lyrae – stars: abun-dances – stars: evolution – stars: fundamental parameters