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

We derive the basic physical parameters of the field double-mode RR Lyrae star BS Com from its observed periods and the requirement of consistency between the pulsational and evolutionary constraints. By using the current solar-scaled horizontal branch evolutionary models of Pietrinferni et al. and our linear non-adiabatic purely radiative pulsational models, we get M/M⊙= 0.698 ± 0.004, log(L/L⊙) = 1.712 ± 0.005, Teff= 6840 ± 14 K, [Fe/H]=−1.67 ± 0.01, where the errors are standard deviations assuming uniform age distribution along the full range of uncertainty in age. The last two parameters are in a good agreement with the ones derived from the observed BVIC colours and the updated atlas9 stellar atmosphere models. We get Teff= 6842 ± 10 K, [Fe/H]=−1.58 ± 0.11, where the errors are purely statistical ones. It is remarkable that the derived parameters are nearly independent of stellar age at early evolutionary stages. Later stages, corresponding to the evolution towards the asymptotic giant branch, are most probably excluded because the required high temperatures are less likely to satisfy the constraints posed by the colours. We also show that our conclusions are only weakly sensitive to non-linear period shifts predicted by current hydrodynamical model

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 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.Comment: Accepted for publication in MNRAS. 15 pages, 14 figures, and 7 printed tables (2 of them available in electronic form

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 percent 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.Comment: 10 figures, 2 tables. Accepted for publication in MNRA

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 MW Lyrae (MW Lyr) during the 2006-2007 observing seasons. The data within each 0.05 phase bin of the modulation period (Pm=f−1m) cover the entire light cycle of the primary pulsation period (P0=f−10), 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 fm, sidelobe modulation frequencies around the pulsation frequency and its harmonics appear at ±2fm, ±4fm and ±12.5fm 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 Φ21, Φ31 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 phase

The all-sky GEOS RR Lyr survey with the TAROT telescopes. Analysis of the Blazhko effect

We used the GEOS database to study the Blazhko effect of galactic RRab stars. The database is continuously enriched by maxima supplied by amateur astronomers and by a dedicated survey by means of the two TAROT robotic telescopes. The same value of the Blazhko period is observed at different values of the pulsation periods and different values of the Blazhko periods are observed at the same value of the pulsation period. There are clues suggesting that the Blazhko effect is changing from one cycle to the next. The secular changes in the pulsation and Blazhko periods of Z CVn are anticorrelated. The diagrams of magnitudes against phases of the maxima clearly show that the light curves of Blazhko variables can be explained as modulated signals, both in amplitude and in frequency. The closed curves describing the Blazhko cycles in such diagrams have different shapes, reflecting the phase shifts between the epochs of the brightest maximum and the maximum O-C. Our sample shows that both clockwise and anticlockwise directions are possible for similar shapes. The improved observational knowledge of the Blazhko effect, in addition to some peculiarities of the light curves, have still to be explained by a satisfactory physical mechanism.Comment: 13 pages, 12 figures, accepted for publication in Astronomical Journa

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 perio

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

We derive the basic physical parameters of the field double-mode RR Lyrae star BS Com from its observed periods and the requirement of consistency between the pulsational and evolutionary constraints. By using the current solar-scaled horizontal branch evolutionary models of Pietrinferni et al. (2004) and our linear non-adiabatic purely radiative pulsational models, we get M/M(Sun) = 0.698 +/- 0.004, log(L/L(Sun)) = 1.712 +/- 0.005, T(eff) = 6840 +/- 14 K, [Fe/H] = -1.67 +/- 0.01, where the errors are standard deviations assuming uniform age distribution along the full range of uncertainty in age. The last two parameters are in a good agreement with the ones derived from the observed BVIc colours and the updated ATLAS9 stellar atmosphere models. We get T(eff) = 6842 +/- 10 K, [Fe/H] = -1.58 +/- 0.11, where the errors are purely statistical ones. It is remarkable that the derived parameters are nearly independent of stellar age at early evolutionary stages. Later stages, corresponding to the evolution toward the asymptotic giant branch are most probably excluded because the required high temperatures are less likely to satisfy the constraints posed by the colours. We also show that our conclusions are only weakly sensitive to nonlinear period shifts predicted by current hydrodynamical models.Comment: Accepted for publication by MNRAS on 2008 February 01. The paper contains 4 figures and 8 table