139 research outputs found
The Blazhko effect and additional excited modes in RR Lyrae stars
Recent photometric space missions, such as CoRoT and Kepler revealed that
many RR Lyrae stars pulsate -- beyond their main radial pulsation mode -- in
low amplitude modes. Space data seem to indicate a clear trend, namely overtone
(RRc) stars and modulated fundamental (RRab) RR Lyrae stars ubiquitously show
additional modes, while non-Blazhko RRab stars never do. Two Kepler stars (V350
Lyr and KIC 7021124), however, apparently seemed to break this rule: they were
classified as non-Blazhko RRab stars showing additional modes. We processed
Kepler pixel photometric data of these stars. We detected small amplitude, but
significant Blazhko effect for both stars by using the resulted light curves
and OC diagrams. This finding strengthens the apparent connection between
the Blazhko effect and the excitation of additional modes. In addition, it
yields a potential tool for detecting Blazhko stars through the additional
frequency patterns even if we have only short but accurate time series
observations. V350 Lyr shows the smallest amplitude multiperiodic Blazhko
effect ever detected.Comment: 6 pages, 4 figures and 2 tables. Accepted for publication in ApJ
Letter
Kepler RR Lyrae stars: beyond period doubling
We examined the complete short cadence sample of 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. In three cases we observe the
interaction of three different modes. Since the period ratios are close to
resonant values, we observe quasi-repetiting patterns in the pulsation cycles
in the stars. These findings support the mode-resonance explanations of the
Blazhko effect.Comment: 2 pages, 1 figure. Proceedings of the 301st IAU Symposium, Precision
Asteroseismology, August 2013, Wroc{\l}aw. V2: small corrections to the
wordin
Nonlinear dynamical analysis of the Blazhko effect with the Kepler space telescope: the case of V783 Cyg
We present a detailed nonlinear dynamical investigation of the Blazhko
modulation of the Kepler RR Lyrae star V783 Cyg (KIC 5559631). We used
different techniques to produce modulation curves, including the determination
of amplitude maxima, the O-C diagram and the analytical function method. We
were able to fit the modulation curves with chaotic signals with the global
flow reconstruction method. However, when we investigated the effects of
instrumental and data processing artefacts, we found that the chaotic nature of
the modulation can not be proved because of the technical problems of data
stitching, detrending and sparse sampling. Moreover, we found that a
considerable part of the detected cycle-to-cycle variation of the modulation
may originate from these effects. According to our results, even the
four-year-long, unprecedented Kepler space photometry of V783 Cyg is too short
for a reliable nonlinear dynamical analysis aiming at the detection of chaos
from the Blazhko modulation. We estimate that two other stars could be suitable
for similar analysis in the Kepler sample and in the future TESS and PLATO may
provide additional candidates.Comment: 9 pages, 12 figures, accepted for publication in MNRA
Long time-scale behavior of the Blazhko effect from rectified Kepler data
In order to benefit from the 4-year unprecedented precision of the Kepler
data, we extracted light curves from the pixel photometric data of the Kepler
space telescope for 15 Blazhko RR Lyrae stars. For collecting all the flux from
a given target as accurately as possible, we defined tailor-made apertures for
each star and quarter. In some cases the aperture finding process yielded
sub-optimal result, because some flux have been lost even if the aperture
contains all available pixels around the star. This fact stresses the
importance of those methods that rely on the whole light curve instead of
focusing on the extrema (O-C diagrams and other amplitude independent methods).
We carried out detailed Fourier analysis of the light curves and the amplitude
independent O-C diagram. We found 12 (80%) multiperiodically modulated stars in
our sample. This ratio is much higher than previously found. Resonant coupling
between radial modes, a recent theory to explain of the Blazhko effect, allows
single, multiperiodic or even chaotic modulations. Among the stars with two
modulations we found three stars (V355 Lyr, V366 Lyr and V450 Lyr) where one of
the periods dominate in amplitude modulation, but the other period has larger
frequency modulation amplitude. The ratio between the primary and secondary
modulation periods is almost always very close to ratios of small integer
numbers. It may indicate the effect of undiscovered resonances. Furthermore, we
detected the excitation of the second radial overtone mode for three
stars where this feature was formerly unknown. Our data set comprises the
longest continuous, most precise observations of Blazhko RR Lyrae stars ever
published. These data which is made publicly available will be unprecedented
for years to come.Comment: 19 pages, 17 figures, accepted for publication in Astrophys. J.
Suppl. Rectified data are here: http://www.konkoly.hu/KIK/data.htm
Revisiting CoRoT RR Lyrae stars: detection of period doubling and temporal variation of additional frequencies
We search for signs of period doubling in CoRoT RR Lyrae stars. The
occurrence of this dynamical effect in modulated RR Lyrae stars might help us
to gain more information about the mysterious Blazhko effect. The temporal
variability of the additional frequencies in representatives of all subtypes of
RR Lyrae stars is also investigated. We pre-process CoRoT light curves by
applying trend and jump correction and outlier removal. Standard Fourier
technique is used to analyze the frequency content of our targets and follow
the time dependent phenomena. The most comprehensive collection of CoRoT RR
Lyrae stars, including new discoveries is presented and analyzed. We found
alternating maxima and in some cases half-integer frequencies in four CoRoT
Blazhko RR Lyrae stars, as clear signs of the presence of period doubling. This
reinforces that period doubling is an important ingredient to understand the
Blazhko effect - a premise we derived previously from the Kepler RR Lyrae
sample. As expected, period doubling is detectable only for short time
intervals in most modulated RRab stars. Our results show that the temporal
variability of the additional frequencies in all RR Lyrae sub-types is
ubiquitous. The ephemeral nature and the highly variable amplitude of these
variations suggest a complex underlying dynamics of and an intricate interplay
between radial and possibly nonradial modes in RR Lyrae stars. The omnipresence
of additional modes in all types of RR Lyrae - except in non-modulated RRab
stars - implies that asteroseismology of these objects should be feasible in
the near future (Abridged).Comment: 20 pages, 13 figures, accepted for publication in A&
The CoRoT star 105288363: strong cycle to cycle changes of the Blazhko modulation
We present the analysis of the CoRoT star 105288363, a new Blazhko RR Lyrae
star of type RRab (f0 = 1.7623 c/d), observed with the CoRoT space craft during
the second long run in direction of the galactic center (LRc02, time base 145
d). The CoRoT data are characterized by an excellent time sampling and a low
noise amplitude of 0.07 mmag in the 2-12 c/d range and allow us to study not
only the fine details of the variability of the star but also long-term changes
in the pulsation behaviour and the stability of the Blazhko cycle. We use,
among other methods, standard Fourier analysis techniques and O-C diagrams to
investigate the pulsational behavior of the Blazhko star 105288363. In addition
to the frequency pattern expected for a Blazhko RR Lyrae star, we find an
independent mode (f1 = 2.984 c/d) showing a f0/f1 ratio of 0.59 which is
similar to that observed in other Blazhko RR Lyrae stars. The bump and hump
phenomena are also analysed, with their variations over the Blazhko cycle. We
carefully investigated the strong cycle-to-cycle changes in the Blazhko
modulation (PB = 35.6 d), which seem to happen independently and partly
diametrically in the amplitude and the phase modulation. Furthermore, the
phasing between the two types of modulation is found to change during the
course of the observations.Comment: 15 pages, 8 figures, accepted for publication in MNRA
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