Period Doubling in Kepler RR 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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Kepler RR Lyrae stars: beyond period doubling

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313015044 ◽

2013 ◽

Vol 9 (S301) ◽

pp. 459-460

Author(s):

L. Molnár ◽

J. M. Benkő ◽

R. Szabó ◽

Z. Kolláth

Keyword(s):

Fundamental Mode ◽

Period Doubling ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Blazhko Effect ◽

Lyrae Stars

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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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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RR Lyrae studies with Kepler: showcasing RR Lyr

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313014415 ◽

2013 ◽

Vol 9 (S301) ◽

pp. 257-260

Author(s):

Katrien Kolenberg ◽

Robert L. Kurucz ◽

Robert Stellingwerf ◽

James M. Nemec ◽

Paweł Moskalik ◽

...

Keyword(s):

Period Doubling ◽

Theoretical Modelling ◽

Occurrence Rate ◽

Short Paper ◽

Physical Parameters ◽

Rr Lyrae Stars ◽

Pulsating Stars ◽

Rr Lyrae ◽

Lyrae Stars ◽

Insight Into

AbstractFour years into the Kepler mission, an updated review on the results for RR Lyrae stars is in order. More than 50 RR Lyrae stars in the Kepler field are observed with Kepler and each one of them can provide us with new insight into this class of pulsating stars. Ground-based spectroscopy of the Kepler targets allows us to narrow down their physical parameters. Previously, we already reported a 50% occurrence rate of modulation in the RRab stars, a large variety of modulation behavior, period doubling in several Blazhko stars, the detection of higher- overtone radial modes, probable non-radial modes and new types of multiple-mode RR Lyrae pulsators, among both the RRab and the RRc stars. In addition, the quasi-continuous photometry obtained over several years with Kepler allows one to observe changes in Blazhko behavior and additional longer cycles. These observations have sparked new theoretical modelling efforts. In this short paper we showcase RR Lyr itself. The star has been observed with Kepler in short cadence, and some remarkable features of its pulsation behavior are unveiled in this long-studied prototype, through the Kepler photometry and additional spectroscopic data.

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The Unusual Period Distribution of the RR Lyrae Variables in NGC 5897

International Astronomical Union Colloquium ◽

10.1017/s0252921100011957 ◽

1989 ◽

Vol 111 ◽

pp. 287-287

Author(s):

Amelia Wehlau

Keyword(s):

Light Curves ◽

Instability Strip ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

Period Distribution ◽

Unusual Distribution ◽

Photoelectric Observations ◽

Lyrae Stars ◽

Branch Star ◽

Central Concentration

AbstractAttention is called to the rather unusual distribution of the periods of the RR Lyrae variables in NGC 5897, a metal-poor halo globular cluster with a very low central concentration. Of the seven RR Lyrae stars known in the cluster, three have periods between 0.797 and 0.856 day and two have periods of 0.45 and 0.42 day. The other two have periods of 0.34 and 0.35 day with much lower amplitudes of variation. Due to the lack of crowding in this cluster photoelectric observations and Fourier decompositions of the resulting light curves should be possible for at least six of the RR Lyrae variables. In addition, the cluster appears to contain a non-variable horizontal branch star, SK 120, lying within the instability strip. As this is the only well documented case of such a star, photoelectric observations of this star would also be desirable.

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General Properties of the Two Groups of Globular Clusters and Their Variable Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900010743 ◽

1975 ◽

Vol 67 ◽

pp. 541-543

Author(s):

A. V. Mironov ◽

N. N. Samus'

Keyword(s):

Chemical Composition ◽

Globular Clusters ◽

Variable Stars ◽

Rr Lyrae Stars ◽

General Properties ◽

Rr Lyrae ◽

Lyrae Stars

The dependences of the numbers of variable stars in globular clusters on the chemical composition are studied. For given metallicity the numbers of RR Lyrae stars reduced to some definite total number of stars in the cluster are different for the two groups of globular clusters introduced by Mironov.

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