167 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
Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models -- III. SW And, DH Peg, CU Com, DY Peg
We report the most comprehensive UBV(RI)_C observations of the bright,
radially pulsating field stars SW And, DH Peg, CU Com, DY Peg. Long term
variation has been found in the ultraviolet colour curves of SW And and DH Peg.
We apply our photometric-hydrodynamic method to determine the fundamental
parameters of these stars: metallicity, reddening, distance, mass, radius,
equilibrium luminosity and effective temperature. Our method works well for SW
And, CU Com and DY Peg. A very small mass 0.26+/-0.04 M_Sun of SW And has been
found. The fundamental parameters of CU Com are those of a normal double-mode
RR Lyrae (RRd) star. DY Peg has been found to have paradoxical astrophysical
parameters: the metallicity, mass and period are characteristic for a
high-amplitude Delta Sct star while the luminosity and radius place it in the
group of RR Lyrae stars. DH Peg has been found to be peculiar: the definite
instability in the colour curves towards ultraviolet, the dynamical variability
of the atmosphere during the shocked phases suggests that the main assumptions
of our photometric-hydrodynamic method, the quasi-static atmosphere
approximation (QSAA) and the exclusive excitation of radial modes are probably
not satisfied in this star. The fundamental parameters of all stars studied in
this series of papers are summarized in tabular and graphical form.Comment: 15 pages, 10 figures; accepted for publication in MNRA
Unexpected series of regular frequency spacing of delta Scuti stars in the non-asymptotic regime -- I. The methodology
A sequence search method was developed to search regular frequency spacing in
delta Scuti stars by visual inspection and algorithmic search. We searched for
sequences of quasi-equally spaced frequencies, containing at least four members
per sequence, in 90 delta Scuti stars observed by CoRoT. We found an
unexpectedly large number of independent series of regular frequency spacing in
77 delta Scuti stars (from 1 to 8 sequences) in the non-asymptotic regime. We
introduce the sequence search method presenting the sequences and echelle
diagram of CoRoT 102675756 and the structure of the algorithmic search. Four
sequences (echelle ridges) were found in the 5-21 d^{-1} region, where the
pairs of the sequences are shifted (between 0.5-0.59 d^{-1}) by twice the value
of the estimated rotational splitting frequency (0.269 d^{-1}). The general
conclusions for the whole sample are also presented in this paper. The
statistics of the spacings derived by the sequence search method, by FT and
that of the shifts are also compared. In many stars, more than one almost
equally valid spacing appeared. The model frequencies of FG Vir and their
rotationally split components were used to reveal a possible explanation that
one spacing is the large separation, while the other is a sum of the large
separation and the rotational frequency. In CoRoT 102675756, the two spacings
(2.249 and 1.977 d^{-1}) agree better with the sum of a possible 1.710 d^{-1}
large separation and two or one times, respectively, the value of the
rotational frequency.Comment: 12 pages, 10 figures, accepted for publication in Ap
Unexpected series of regular frequency spacing of delta Scuti stars in the non-asymptotic regime -- II. Sample -- echelle diagrams and rotation
A sequence search method was developed for searching for regular frequency
spacing in delta Scuti stars by visual inspection and algorithmic search. The
sample contains 90 delta Scuti stars observed by CoRoT. An example is given to
represent the visual inspection. The algorithm (SSA) is described in detail.
The data treatment of the CoRoT light curves, the criteria for frequency
filtering and the spacings derived by two methods (three approaches: VI, SSA
and FT) are given for each target. Echelle diagrams are presented for 77
targets, for which at least one sequence of regular spacing was identified.
Comparing the spacing and the shifts between pairs of echelle ridges revealed
that at least one pair of echelle ridges is shifted to midway between the
spacing for 22 stars. The estimated rotational frequencies compared to the
shifts revealed rotationally split doublets, triplets and multiplets not only
for single frequencies, but for the complete echelle ridges in 31 delta Scuti
stars. Using several possible assumptions for the origin of the spacings, we
derived the large separation (), which are distributed along the
mean density versus large separations relation derived from stellar models
Suarez 2014.Comment: 25 pages, 16 figures, 9 tables. Accepted for publication in ApJ
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
On the interchange of alternating-amplitude pulsation cycles
We characterized the time intervals between the interchanges of the
alternating high- and low-amplitude extrema of three RV Tauri and three RR
Lyrae stars.Comment: 2 pages, Proceedings of the 301st IAU Symposium, Precision
Asteroseismology, August 201
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
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