We present our analysis of Kepler observations of 29 RR Lyrae stars, based on 138 d of observation. We report precise pulsation periods for all stars. Nine of these stars had incorrect or unknown ...periods in the literature. 14 of the stars exhibit both amplitude and phase Blazhko modulations, with Blazhko periods ranging from 27.7 to more than 200 d. For V445 Lyr, a longer secondary variation is also observed in addition to its 53.2-d Blazhko period. The unprecedented precision of the Kepler photometry has led to the discovery of the the smallest modulations detected so far. Moreover, additional frequencies beyond the well-known harmonics and Blazhko multiplets have been found. These frequencies are located around the half-integer multiples of the main pulsation frequency for at least three stars. In four stars, these frequencies are close to the first and/or second overtone modes. The amplitudes of these periodicities seem to vary over the Blazhko cycle. V350 Lyr, a non-Blazhko star in our sample, is the first example of a double-mode RR Lyrae star that pulsates in its fundamental and second overtone modes.
In order to investigate the time variations and the peculiarities of the optical spectra of the RV Tauri star R Sct, high-resolution spectroscopic observations in the wavelength interval around the
...line (6540–6580 Å) were obtained between 2014 and 2018. The phase dependence of the equivalent widths and radial velocities was measured for the
and Fe I
5669.224 Å lines, respectively.
shows considerable changes in its line profile. We observed double-peaked emission and an inverse P Cygni profile in this line. We detected a variation from inverse P Cygni to P Cygni profile for both Ti I
6554.239 Å and Ca I
6572.797 Å lines at phases where the shock wave is propagating through the atmospheric layer in which the H
α
lines are forming, particularly around
which is just after the deep minimum and
, just after shallow minimum. An increase in the shock wave velocity generates a decrease in the
intensity, which is explained by the ionization phenomenon. The detailed description of the variations in R Sct reveals its important properties. The observation of the P Cygni and the inverse P Cygni profile indicate that expanding and infalling layers are simultaneously present in the stellar atmosphere, pointing out the complicated nature of this object.
Context. The influence of binarity on the late stages of stellar evolution remains an open issue. Aims. While the first binary post-AGB stars were serendipitously discovered, the distinct ...characteristics of their spectral energy distribution (SED) allowed us to launch a more systematic search for binaries. We selected post-AGB objects, which exhibit a broad dust excess starting either at H or K, pointing to the presence of a gravitationally bound dusty disc in the system. We initiated an extensive multiwavelength study of those systems and here report on our radial velocity and photometric monitoring results for six stars of early F type, which are pulsators of small amplitude. Methods. To determine the radial velocity of low signal-to-noise ratio time-series data, we constructed dedicated autocorrelation masks based on high signal-to-noise ratio spectra, used in our published chemical studies. The radial velocity variations were analysed in detail to differentiate between pulsational variability and variability caused by orbital motion. When available, the photometric monitoring data were used to complement the time series of radial velocity data and to establish the nature of the pulsation. Finally, orbital minimalisation was performed to constrain the orbital elements. Results. All of the six objects are binaries with orbital periods ranging from 120 to 1800 days. Five systems have non-circular orbits. The mass functions range from 0.004 to 0.57 $M_{\odot}$ and the companions are probably unevolved objects of (very) low initial mass. We argue that these binaries must have evolved through a phase of strong binary interaction when the primary was a cool supergiant. Although the origin of the circumstellar disc is not well understood, the disc is generally believed to have formed during this strong interaction phase. The eccentric orbits of these highly evolved objects remain poorly understood. In one object, the line-of-sight grazes the edge of the puffed-up inner rim of the disc. Conclusions. These results corroborate our earlier statement that evolved objects in binary stars create a Keplerian dusty circumbinary disc. With the measured orbits and mass functions, we conclude that the circumbinary discs seem to have a major impact on the evolution of a significant fraction of binary systems.
Rapid and strong changes in the Blazhko modulation of RR Lyrae stars, as have recently been detected in high-precision satellite data, have become a crucial topic in finding an explanation of the ...long-standing mystery of the Blazhko effect. We present here an analysis of the most extreme case detected so far, the RRab star V445 Lyr (KIC 6186029) which was observed with the Kepler space mission. V445 Lyr shows very strong cycle-to-cycle changes in its Blazhko modulation, which are caused by both a secondary long-term modulation period and irregular variations. In addition to the complex Blazhko modulation, V445 Lyr also shows a rich spectrum of additional peaks in the frequency range between the fundamental pulsation and the first harmonic. Among those peaks, the second radial overtone could be identified, which, combined with a metallicity estimate of Fe/H =−2.0 dex from spectroscopy, allowed us to constrain the mass (0.55-0.65 M⊙) and luminosity (40-50 L⊙) of V445 Lyr through theoretical Petersen diagrams. A non-radial mode and possibly the first overtone are also excited. Furthermore, V445 Lyr shows signs of the period-doubling phenomenon and a long-term period change. A detailed Fourier analysis along with a study of the O − C variation of V445 Lyr is presented, and the origin of the additional peaks and possible causes of the changes in the Blazhko modulation are discussed. The results are then put into context with those of the only other star with a variable Blazhko effect for which a long enough set of high-precision continuous satellite data has been published so far, the CoRoT star 105288363.
The observations of the Kepler Space Telescope revealed that fundamental-mode RR Lyrae stars may show various radial overtones. The presence of multiple radial modes may allow us to conduct nonlinear ...asteroseismology: comparison of mode amplitudes and frequency shifts between observations and models. Here we report the detection of three radial modes in the star RR Lyr, the eponym of the class, using the Kepler short cadence data: besides the fundamental mode, both the first and the ninth overtones can be derived from the data set. RR Lyrae shows period doubling, but switches occasionally to a state where a pattern of six pulsation cycles repeats instead of two. We found hydrodynamic models that show the same three modes and the period-six state, allowing for comparison with the observations.
Nineteen of the ∼40 RR Lyr stars in the Kepler field have been identified as candidate non-Blazhko (or unmodulated) stars. In this paper we present the results of Fourier decomposition of the ...time-series photometry of these stars acquired during the first 417 d of operation (Q0-Q5) of the Kepler telescope. Fourier parameters based on ∼18 400 long-cadence observations per star (and ∼150 000 short-cadence observations for FN Lyr and for AW Dra) are derived. None of the stars shows the recently discovered 'period-doubling' effect seen in Blazhko variables; however, KIC 7021124 has been found to pulsate simultaneously in the fundamental and second overtone modes with a period ratio P
2/P
0∼ 0.593 05 and is similar to the double-mode star V350 Lyr. Period change rates are derived from O − C diagrams spanning, in some cases, over 100 years; these are compared with high-precision periods derived from the Kepler data alone. Extant Fourier correlations by Kovács, Jurcsik et al. (with minor transformations from the V to the Kp passband) have been used to derive underlying physical characteristics for all the stars. This procedure seems to be validated through comparisons of the Kepler variables with Galactic and Large Magellanic Cloud (LMC) RR Lyr stars. The most metal-poor star in the sample is NR Lyr, with Fe/H =−2.3 dex; and the four most metal-rich stars have Fe/H ranging from −0.6 to +0.1 dex. Pulsational luminosities and masses are found to be systematically smaller than L and
values derived from stellar evolution models, and are favoured over the evolutionary values when periods are computed with the Warsaw linear hydrodynamics code. Finally, the Fourier parameters are compared with theoretical values derived using the Warsaw non-linear convective pulsation code.
Context. The knowledge of accurate stellar parameters is a keystone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the fundamental parameters can ...be derived from both spectroscopy and multicolour photometry, the results obtained are sometimes affected by systematic uncertainties. Stellar pulsation reaches high amplitudes in RR Lyrae stars, and as a consequence the stellar parameters vary significantly over the pulsation cycle. The abundances of the star, however, are not expected to change. Aims. We present a self-consistent spectral analysis of the pulsating star RR Lyr, which is the primary target of our study of the Blazhko effect. Methods. We used high-resolution and high signal-to-noise ratio spectra to carry out a consistent parameter determination and abundance analysis for RR Lyr. The LLmodels code was employed for model atmosphere calculations, while the SYNTH3 and WIDTH9 codes were used for line profile calculations and LTE abundance analysis. We describe in detail the methodology adopted to derive the fundamental parameters and the abundances. From a set of available high-resolution spectra of RR Lyr, we selected the phase of maximum radius at which the spectra are least disturbed by the pulsation. Using the abundances determined at this phase as a starting point, we expect to be able to determine the fundamental parameters determined at other phases more accurately. Results. The set of fundamental parameters obtained in this work fits the observed spectrum accurately. From the abundance analysis, we find clear indications of a depth-dependent microturbulent velocity, that we quantify. Conclusions. We confirm the importance of a consistent analysis of relevant spectroscopic features, the application of advanced model atmospheres, and the use of up-to-date atomic line data for determining stellar parameters. These results are crucial for further studies, e. g., detailed theoretical modelling of the observed pulsations.
We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5 days of science operations, reveal high ...signal-to-noise solar-like oscillation spectra in all three stars: about 20 modes of oscillation may be clearly distinguished in each star. We discuss the appearance of the oscillation spectra, use the frequencies and frequency separations to provide first results on the radii, masses, and ages of the stars, and comment in the light of these results on prospects for inference on other solar-type stars that Kepler will observe.
On the centenary of the discovery of the Blazhko effect 1, it is time to give a rundown of what progress has been made over the past decade in the understanding of the phenomenon. The Blazhko effect ...is a periodic amplitude and/or phase modulation of the light curve, shown by a large fraction of the astrophy sic ally important RR Lyrae stars. Despite numerous devoted observational studies and elaborate models attempting to reproduce the modulation, it still defies a definitive explanation. This paper attempts to give an overview of the observational and theoretical status of studies devoted to the phenomenon.
RR Lyr is one of the most studied variable stars. Its light curve has been regularly monitored since the discovery of its periodic variability in 1899. The analysis of all observed maxima allows us ...to identify two primary pulsation states, defined as pulsation over a long (P
0 longer than 0.56684 d) and a short (P
0 shorter than 0.56682 d) primary pulsation period. These states alternate with intervals of 13–16 yr, and are well defined after 1943. The 40.8-d periodical modulations of the amplitude and the period (i.e. the Blazhko effect) were noticed in 1916. We provide homogeneous determinations of the Blazhko period in the different primary pulsation states. The Blazhko period does not follow the variations of P
0 and suddenly diminished from 40.8 d to around 39.0 d in 1975. The monitoring of these periodicities deserved, and still deserves, a continuous and intensive observational effort. For this purpose, we have built dedicated, transportable and autonomous small instruments, Very Tiny Telescopes (VTTs), to observe the times of maximum brightness of RR Lyr. As immediate results, the VTTs recorded the last change of the P
0 state in mid-2009 and extended the time coverage of the Kepler observations, thus recording a maximum O − C amplitude of the Blazhko effect at the end of 2008, followed by the historically smallest O − C amplitude in late 2013. This decrease is still ongoing and the VTTs are ready to monitor the expected increase in the next few years.
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