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Register a new userThe additional-mode garden of RR Lyrae stars
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Space-based photometric missions revealed a surprising abundance of millimagnitude-level additional modes in RR Lyrae stars. The modes that appear in the modulated fundamental-mode (RRab) stars can be ordered into four major categories. Here we present the distribution of these groups in the Petersen diagram, and discuss their characteristics and connections to additional modes observed in other RR Lyrae stars.
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Classical double-mode pulsators (RR Lyrae stars and delta Cepheids) are important for their simultaneous pulsation in low-order radial modes. This enables us to put stringent constraints on their physical parameters. We use 30 bright galactic double-mode RR~Lyrae (RRd) stars to estimate their luminosities and compare them with those derived from the parallaxes of the recent data release (EDR3) of the Gaia survey. We employ pulsation and evolutionary models, together with observationally determined effective temperatures to derive the basic stellar parameters. Excluding 6 outlying stars (e.g., with blending issues) the RRd and Gaia luminosities correlate well. With the adopted temperature zero point from one of the works based on the infrared flux method, we find it necessary to increase the Gaia parallaxes by 0.02 mas to bring the RRd and Gaia luminosities into agreement. This value is consonant with those derived from studies on binary stars in the context of Gaia. We examine also the resulting period-luminosity-metallicity (PLZ) relation in the 2MASS K band as follows from the RRd parameters. This leads to the verification of two independently derived other PLZs. No significant zero point differences are found. Furthermore, the predicted K absolute magnitudes agree within sigma=0.005-0.01mag.
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).
In an era of extensive photometric observations, the catalogs of RR Lyr type variable stars number tens of thousands of objects. The relation between the iron abundance [Fe/H] and the Fourier parameters of the stars light curve allows us to investigate mean metallicities and metallicity gradients in various stellar environments, independently of time-consuming spectroscopic observations. In this paper we use almost 6500 $V$- and $I$-band light curves of fundamental mode RR Lyr stars from the OGLE-IV survey to provide a relation between the $V$- and $I$-band phase parameter $varphi_{31}$ used to estimate [Fe/H]. The relation depends on metallicity, which limits its applicability. We apply this relation to metallicity formulae developed for the Johnson $V$- and the Kepler $Kp$-band to obtain the relation between [Fe/H] and $varphi_{31}$ for the $I$-band photometry. Last, we apply the new relation of Nemec to the OGLE-IV fundamental mode RR Lyr stars data and construct a metallicity map of the Magellanic Clouds. Median [Fe/H] is $-1.39pm0.44$ dex for the LMC and $-1.77pm0.48$ dex for the SMC, on the Jurcsik metallicity scale. We also find a metallicity gradient within the LMC with a slope of $-0.029pm0.002$ dex/kpc in the inner 5 kpc and $-0.030 pm0.003$ dex/kpc beyond 8 kpc, and no gradient in-between ($-0.019pm0.002$ dex/kpc integrally). We do not observe a metallicity gradient in the SMC, although we show that the metal-rich RRab stars are more concentrated toward the SMC center than the metal-poor.
RR Lyrae stars for a long time had the reputation of being rather simple pulsators, but the advent of high-precision space photometry has meanwhile changed this picture dramatically. This article summarizes the results obtained for two remarkable Blazhko RR Lyrae stars and discusses how our view of RR Lyrae stars has changed since the availability of ultra-precise satellite photometry as it is obtained by CoRoT and Kepler. Both stars, CoRoT 105288363 and V445 Lyrae, show a multitude of phenomena that were impossible to observe from the ground, either because of the small amplitude of the effect, or because uninterrupted long-term monitoring was required for a detection. Not only was it found that strong and irregular cycle-to-cycle changes of the Blazhko effect can occur, and that seemingly chaotic phenomena need to be accounted for when modeling the Blazhko effect, but also a rich spectrum of low-amplitude frequencies was detected in addition to the fundamental radial pusation in RRab stars. The so-called period doubling phenomenon, higher radial overtones and possibly also non-radial modes make RR Lyrae stars more multifaceted than previously thought. This article presents the various aspects of irregularity of the Blazhko effect, questioning its long-standing definition as a periodic modulation, and also discusses the low-amplitude pulsation signatures that had been hidden in the noise of observations for centuries.
We analysed 30 RR Lyrae stars (RRLs) located in the Large Magellanic Cloud (LMC) globular cluster Reticulum that were observed in the 3.6 and 4.5 $mu$m passbands with the Infrared Array Camera (IRAC) on board of the Spitzer Space Telescope. We derived new mid-infrared (MIR) period-luminosity PL relations. The zero points of the PL relations were estimated using the trigonometric parallaxes of five bright Milky Way (MW) RRLs measured with the Hubble Space Telescope (HST) and, as an alternative, we used the trigonometric parallaxes published in the first Gaia data release (DR1) which were obtained as part of the Tycho-Gaia Astrometric Solution (TGAS) and the parallaxes of the same stars released with the second Gaia data release (DR2). We determined the distance to Reticulum using our new MIR PL relations and found that distances calibrated on the TGAS and DR2 parallaxes are in a good agreement and, generally, smaller than distances based on the HST parallaxes, although they are still consistent within the respective errors. We conclude that Reticulum is located ~3 kpc closer to us than the barycentre of the LMC.
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