Kepler RR Lyrae stars: beyond period doubling

AbstractWe examined the complete short cadence sample of fundamental-mode Kepler RR Lyrae stars to further investigate the recently discovered dynamical effects such as period doubling and additional modes. Here we present the findings on four stars. V450 Lyr may be a non-classical double-mode RR Lyrae star pulsating in the fundamental mode and the second overtone. For the three remaining stars we observe the interaction of three different modes. Since the period ratios are close to resonant values, we observe quasi-repetitive patterns in the pulsation cycles in the stars. These findings support the mode-resonance explanations of the Blazhko effect.

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Blazhko effect in the Galactic bulge fundamental mode RR Lyrae stars – I. Incidence rate and differences between modulated and non-modulated stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stw3231 ◽

2017 ◽

Vol 466 (3) ◽

pp. 2602-2613 ◽

Cited By ~ 15

Author(s):

Z. Prudil ◽

M. Skarka

Keyword(s):

Incidence Rate ◽

Fundamental Mode ◽

Galactic Bulge ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Blazhko Effect ◽

Lyrae Stars

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Blazhko effect in Cepheids and RR Lyrae stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313014397 ◽

2013 ◽

Vol 9 (S301) ◽

pp. 241-248

Author(s):

Róbert Szabó

Keyword(s):

Time Series Data ◽

Period Doubling ◽

High Order ◽

Series Data ◽

Theoretical Point ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Starting Point ◽

Blazhko Effect ◽

Lyrae Stars

AbstractThe 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, such as extreme modulations, irregular modulation cycles and additional periodicities. I argue that these findings together with dedicated ground-based efforts provide us now 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.

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Does Kepler unveil the mystery of the Blazhko effect? First detection of period doubling in Kepler Blazhko RR Lyrae stars

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2010.17386.x ◽

2010 ◽

Vol 409 (3) ◽

pp. 1244-1252 ◽

Cited By ~ 93

Author(s):

R. Szabó ◽

Z. Kolláth ◽

L. Molnár ◽

K. Kolenberg ◽

D. W. Kurtz ◽

...

Keyword(s):

Period Doubling ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Blazhko Effect ◽

Lyrae Stars

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Are RRab stars fully radial?

Proceedings of the International Astronomical Union ◽

10.1017/s174392131301466x ◽

2013 ◽

Vol 9 (S301) ◽

pp. 383-384 ◽

Cited By ~ 1

Author(s):

József M. Benkő ◽

Róbert Szabó

Keyword(s):

Fundamental Mode ◽

Period Doubling ◽

Space Missions ◽

Radial Pulsation ◽

Linear Combinations ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Fourier Spectra ◽

Oscillation Frequencies ◽

Lyrae Stars

AbstractThanks to the space missions CoRoT and Kepler new oscillation frequencies have been discovered in the Fourier spectra of Blazhko RR Lyrae stars. The period doubling (PD) yields half-integer frequencies between the fundamental mode and its harmonics. In many cases the first and/or second radial overtone frequencies also appear temporally. Some stars show extra frequencies that were identified as potential non-radial modes. We show here that all these frequencies can be explained by pure radial pulsation as linear combinations of the frequencies of radial fundamental and overtone modes.

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The K2 RR Lyrae Survey

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318002272 ◽

2017 ◽

Vol 14 (S339) ◽

pp. 83-86

Author(s):

R. Szabó

Keyword(s):

Statistical Study ◽

Period Doubling ◽

Variable Stars ◽

Galactic Structure ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Continuous Coverage ◽

Blazhko Effect ◽

Lyrae Stars

AbstractIn the framework of this project, the K2 RR Lyrae Survey, we proposed to observe thousands of RR Lyrae stars along the Ecliptic in Kepler’s K2 Mission. The high photometric precision and the 80-to-90-day continuous coverage enabled us to investigate in unprecedented detail the light variations of these variable stars which can trace galactic structure. The survey enabled us to conduct a thorough statistical study of RR Lyrae pulsation dynamics, including both old and more recently discovered dynamical phenomena such as resonances, non-radial modes, period doubling and the Blazhko effect. This talk described the K2 RR Lyrae Survey, and discussed the prospects of combining our endeavour with Gaia, LSST and other surveys in the context of studies of Galactic archeology.

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Blazhko effect in the Galactic bulge fundamental mode RR Lyrae stars – II. Modulation shapes, amplitudes, and periods

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa673 ◽

2020 ◽

Vol 494 (1) ◽

pp. 1237-1249

Author(s):

M Skarka ◽

Z Prudil ◽

J Jurcsik

Keyword(s):

Gravitational Lensing ◽

Fundamental Mode ◽

Pulsation Period ◽

Galactic Bulge ◽

Rr Lyrae Stars ◽

Modulation Period ◽

Rr Lyrae ◽

Blazhko Effect ◽

Two Parameters ◽

Lyrae Stars

ABSTRACT The number of stars observed by the Optical Gravitational Lensing Experiment (OGLE) project in the Galactic bulge offers an invaluable chance to study RR Lyrae stars in a statistical manner. We used data of 3141 fundamental-mode RR Lyrae stars showing the Blazhko effect observed in OGLE-IV to investigate a possible connection between modulation amplitudes and periods, light curve, and pulsation characteristics. We found that there is no simple monotonic correlation between any combination of two parameters concerning the Blazhko and pulsation amplitudes, periods, and the shape of the light curves. There are only systematic limits. There is a bottom limit of the modulation period with respect to the pulsation period. We also found that the possible range of modulation amplitudes decreases with increasing pulsation period, which could point towards that the Blazhko effect is suppressed in cooler, larger, more luminous, and less metal abundant bulge RR Lyrae stars. Our investigation revealed that the distribution of the modulation periods can be described with two populations of stars with the mean modulation periods of 48 and 186 d. There is a certain region with a low density of the modulated stars, which we call the Blazhko valley, in the pulsation period–modulation period plane. Based on the similarity of the modulation envelopes, basically every star can be assigned to one of six morphological classes. The double modulation was found in 25 per cent of the studied stars. Only 6.3 per cent of modulated stars belong to the Oosterhoff group II.

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RR Lyrae Stars as Seen by the Kepler Space Telescope

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2020.577695 ◽

2021 ◽

Vol 7 ◽

Author(s):

Emese Plachy ◽

Róbert Szabó

Keyword(s):

Period Doubling ◽

Theoretical Explanation ◽

Theoretical Ground ◽

Rr Lyrae Stars ◽

Space Telescope ◽

Continuous Sampling ◽

Rr Lyrae ◽

Blazhko Effect ◽

Low Amplitude ◽

Lyrae Stars

The unprecedented photometric precision along with the quasi-continuous sampling provided by the Kepler space telescope revealed new and unpredicted phenomena that reformed and invigorated RR Lyrae star research. The discovery of period doubling and the wealth of low-amplitude modes enlightened the complexity of the pulsation behavior and guided us toward nonlinear and nonradial studies. Searching and providing theoretical explanation for these newly found phenomena became a central question, as well as understanding their connection to the oldest enigma of RR Lyrae stars, the Blazhko effect. We attempt to summarize the highest impact RR Lyrae results based on or inspired by the data of the Kepler space telescope both from the nominal and from the K2 missions. Besides the three most intriguing topics, the period doubling, the low-amplitude modes, and the Blazhko effect, we also discuss the challenges of Kepler photometry that played a crucial role in the results. The secrets of these amazing variables, uncovered by Kepler, keep the theoretical, ground-based, and space-based research inspired in the post-Kepler era, since light variation of RR Lyrae stars is still not completely understood.

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