MOST photometry of the RRdLyrae variable AQLeo: two radial modes, 32 combination frequencies and beyond (original) (raw)
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New pulsational properties of eight 'anomalous' RR Lyrae variables
Monthly Notices of the Royal Astronomical Society, 1995
CCD photometry in the V band is presented for 7 eld RR Lyrae stars selected from a sample of eight v ariables which, according to data collected in the literature, are expected to be ab-type pulsators, to have short periods and hence high metallicity, and to be located at high z from the galactic plane. New periods and epochs are derived for them. The new periods are only slightly shorter than the values published on the last edition of the General Catalog of Variable Stars (GCVS4). Instead, in six cases our amplitude of the light v ariation is signicantly smaller than that published on the GCVS4, and in at least three cases the actual pulsation appears to be in the rst harmonic rather than in the fundamental mode. All the suggested c-type pulsators show v ariations in the amplitude and/or quite scattered light curves. Possible explanations are given. From a spectro-photometric analysis of the sample, only DL Com is conrmed to pulsate in the fundamental mode, to have short period, and to be located at relatively high z. A single object cannot be taken as evidence for a signicant metal rich population at large distance from the galactic plane.
Fourier analysis of non-Blazhko ab-type RR Lyrae stars observed with the Kepler space telescope
Monthly Notices of the Royal Astronomical Society, 2011
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 M 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.
Flavours of variability: 29 RR Lyrae stars observed with Kepler
Monthly Notices of the Royal Astronomical Society, 2010
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. Fourteen of the stars exhibit both amplitude and phase Blazhko modulations, with Blazhko periods ranging from 27.7 to more than 200 days. 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 wellknown 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.
Resonant excitation of nonradial modes in RR Lyr stars
A nonlinear development of radial pulsation instability to a resonant excitation of nonradial modes is studied. The theory covers the cases of axisymmetric (m = 0) modes as well as (m, −m) pairs. Adopting a simplified treatment of the mode coupling, it is found that multimode pulsation with constant amplitudes is a highly probable solution. An observable consequence of the m = 0 mode excitation is randomness of pulsation amplitude. The case of an ℓ = 1 mode is the most important because of a small averaging effect and a large excitation probability. A significant amplitude and phase modulation is predicted in the case of excitation of an ℓ = 1, m = ±1 pair. This may explain Blazhko-type modulation in RR Lyrae stars. If this model is correct, the modulation period is determined by the rotation rate and the Brunt-Väisälä frequency in the deepest part of the radiative envelope.
Nonlinear investigation of the pulsational properties of RR Lyrae variables
Astronomy and Astrophysics Supplement Series, 1997
We present a theoretical investigation on periods and amplitudes of RR Lyrae pulsators by adopting stellar parameters which cover the range of theoretical evolutionary expectations. Extensive grids of nonlinear, nonlocal and time-dependent convective RR Lyrae envelope models have been computed to investigate the pulsational behavior in both fundamental and first overtone modes at selected luminosity levels and over an effective temperature range which covers the whole instability region. In order to avoid spurious evaluations of modal stability and pulsation amplitudes, the coupling between pulsation and convection was followed through a direct time integration of the leading equations until radial motions approached their limiting amplitude. Blue and red boundaries for pulsational instability into the HR diagram are presented for three different mass values M = 0.75, 0.65 and 0.58 M , together with an atlas of full amplitude theoretical light curves for both fundamental and first overtone pulsators and for two different assumptions of stellar masses: M = 0.75 and 0.65 M 1 . The dependence of periods on stellar parameters is discussed and new analytical relations connecting the period to the masses, luminosities and effective temperatures are provided. We show that theoretical expectations concerning minimum fundamental periods are in good agreement with the observational evidence of a dichotomic period distribution between different Oosterhoff type clusters. A rather good correlation has been found between the pulsational amplitude of fun-Send offprint requests to: G. Bono
Astronomical Journal, 1999
We present the results of a photometric study of RR Lyrae variables in the Ðeld of the globular cluster M55. We have discovered nine new RR Lyrae stars, increasing the number of known RR Lyrae variables in this cluster to 15 stars. Five of the newly discovered variables are Bailey type RRc, and two are type RRab. Two background RRab stars are probable members of the Sagittarius dwarf galaxy. Fourier decomposition of the light curves was used to derive basic properties of the present sample of RR Lyrae variables. From an analysis of the RRc variables we obtain a mean mass of M \ 0.53^0.03
First CoRoT light curves of RR Lyrae stars
Astronomy and Astrophysics, 2010
Context. The CoRoT-Convection Rotation and planetary Transits-space mission is a great opportunity for monitoring stars with excellent time-sampling and unprecedented photometric precision for up to 150 days. As an important benefit, high-quality RR Lyrae light curves are obtained with a quasi-uninterrupted coverage over several pulsation and Blazhko cycles. Aims. The Blazhko effect in RR Lyrae stars is an unsolved problem of astrophysics. We used the high-precision space data to contribute more precise knowledge to explain the possible physical processes behind the phenomenon. Methods. We applied different period-finding techniques including Period04, MuFrAn, PDM and SigSpec. Amplitude and phase modulation were investigated by an analytical function method as well as with the traditional O-C diagrams. Results. The Blazhko modulation frequency is directly detected in the spectrum, as well as its first and second harmonics. It shows the non-linear nature of the Blazhko modulation. Besides the triplets, further higher-order modulation side peaks appear around the pulsation frequency as quintuplet, septuplet, nonuplet, undecaplet, tredecaplet, quindecaplet and sepdecaplet structures. Additional frequencies, not belonging to the classical multiplet structures, are detected, as well as their linear combinations with the fundamental radial mode. We interpret these additional terms as non-radial modes. During the five consecutive Blazhko cycles, there is a shift of the maximum phase around 0.011 pulsation phase which is likely the consequence of a long term modulation.
Time-resolved CCD photometry and time-series analysis of the RR Lyrae type star RR Gem
Research in Astronomy and Astrophysics, 2019
We present the results of a time-resolved photometric and time-series analysis of an RR Lyrae type star RR Gem. The main results are as follows: we found RR Gem’s pulsation period, 0.39689 d, and its V and I mean magnitudes, 11.277 (V) and 11.063 (I) mag respectively. We confirm its variability type as RRab/BL because it manifests the Blazhko effect, and it also exhibits asymmetric light curves (steep ascending branches), periods from 0.3 to 1.0 d and amplitudes from 0.3 to 2 mag in V. They are fundamental mode pulsators.
MOST photometry and modeling of the rapidly oscillating (roAp) star γ Equulei
Astronomy and Astrophysics, 2008
Aims. Despite photometry and spectroscopy of its oscillations obtained over the past 25 years, the pulsation frequency spectrum of the rapidly oscillating Ap (roAp) star γ Equ has remained poorly understood. Better time-series photometry, combined with recent advances to incorporate interior magnetic field geometry into pulsational models, enable us to perform improved asteroseismology of this roAp star. Methods. We obtained 19 days of continuous high-precision photometry of γ Equ with the M (Microvariability & Oscillations of STars) satellite. The data were reduced with two different reduction techniques and significant frequencies were identified. Those frequencies were fitted by interpolating a grid of pulsation models that include dipole magnetic fields of various polar strengths. Results. We identify 7 frequencies in γ Equ that we associate with 5 high-overtone p-modes and 1st and 2nd harmonics of the dominant p-mode. One of the modes and both harmonics are new discoveries for this star. Our best model solution (1.8 M ⊙ , log T eff ∼ 3.882; polar field strength ∼ 8.1 kG) leads to unique mode identifications for these frequencies (ℓ = 0, 1, 2 and 4). This is the first purely asteroseismic fit to a grid of magnetic models. We measure amplitude and phase modulation of the primary frequency due to beating with a closely spaced frequency that had never been resolved. This casts doubts on theories that such modulationunrelated to the rotation of the star-is due to a stochastic excitation mechanism.
CoRoT light curves of RR Lyrae stars
Astronomy and Astrophysics, 2010
Context. The CoRoT -Convection Rotation and planetary Transits -space mission is a great opportunity for monitoring stars with excellent time-sampling and unprecedented photometric precision for up to 150 days. As an important benefit, high-quality RR Lyrae light curves are obtained with a quasi-uninterrupted coverage over several pulsation and Blazhko cycles. Aims. The Blazhko effect in RR Lyrae stars is an unsolved problem of astrophysics. We used the high-precision space data to contribute more precise knowledge to explain the possible physical processes behind the phenomenon. Methods. We applied different period-finding techniques including Period04, MuFrAn, PDM and SigSpec. Amplitude and phase modulation were investigated by an analytical function method as well as with the traditional O-C diagrams. Results. The Blazhko modulation frequency is directly detected in the spectrum, as well as its first and second harmonics. It shows the non-linear nature of the Blazhko modulation. Besides the triplets, further higher-order modulation side peaks appear around the pulsation frequency as quintuplet, septuplet, nonuplet, undecaplet, tredecaplet, quindecaplet and sepdecaplet structures. Additional frequencies, not belonging to the classical multiplet structures, are detected, as well as their linear combinations with the fundamental radial mode. We interpret these additional terms as non-radial modes. During the five consecutive Blazhko cycles, there is a shift of the maximum phase around 0.011 pulsation phase which is likely the consequence of a long term modulation.