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Post Info TOPIC: RR Lyrae stars
Blobrana


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Posts: 131433
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Blazhko RR Lyrae stars
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Title: AL Pictoris and FR Piscis: two regular Blazhko RR Lyrae stars
Author: Pierre de Ponthiere, Franz-Josef (Josch) Hambsch, Kenneth Menzies, Richard Sabo

The results presented are a continuation of observing campaigns conducted by a small group of amateur astronomers interested in the Blazhko effect of RR Lyrae stars. The goal of these observations is to confirm the RR Lyrae Blazhko effect and to detect any additional Blazhko modulation which cannot be identified from all sky survey data-mining. The Blazhko effect of the two observed stars is confirmed, but no additional Blazhko modulations have been detected.
The observation of the RR Lyrae star AL Pic during 169 nights was conducted from San Pedro de Atacama (Chile). From the observed light curve, 49 pulsation maxima have been measured. Fourier analyses of (O-C), magnitude at maximum light (Mmax) and the complete light curve have provided a confirmation of published pulsation and Blazhko periods, 0.548622 and 34.07 days, respectively. The second multi-longitude observation campaign focused on the RR Lyrae star FR Psc was performed from Europe, United States and Chile. Fourier analyses of the light curve and of 59 measured brightness maxima have improved the accuracy of pulsation and Blazhko periods which are 0.45568 and 51.31 days, respectively. For both stars, no additional Blazhko modulations have been detected.

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Blobrana


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Posts: 131433
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RE: RR Lyrae stars
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Title: RR Lyrae stars seen from space
Authors: Elisabeth Guggenberger

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 modelling 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.

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Blobrana


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Posts: 131433
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Title: Physical parameters of three field RR Lyrae stars
Authors: A. Arellano Ferro, J. H. Pena, R. Figuera Jaimes

Stromgren uvby-\beta photometry of the stars classified as RR Lyrae stars RU Piscium, SS Piscium and TU Ursae Majoris has been used to estimate their iron abundance, temperature, gravity and absolute magnitude. The stability of the pulsating period is discussed. The nature of SS Psc as a RRc or a HADS is addressed. The reddening of each star is estimated from the Stromgren colour indices and reddening sky maps. The results of three approaches to the determination of [Fe/H], T_{eff} and \log(g) are discussed: Fourier light curve decomposition, the Preston \Delta S index and the theoretical grids on the (b-y)_o - c_1{_o} plane.

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Blobrana


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Posts: 131433
Date:
Blazhko stars
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Title: Known Galactic field Blazhko stars
Authors: Marek Skarka

List of known Galactic field stars exhibiting Blazhko effect containing 242 stars is presented. All the entries including their designations, positions, pulsation and Blazhko periods were collected from available literature. Actual values of parameters are given.

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Blobrana


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Posts: 131433
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RE: RR Lyrae stars
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Title: The light-curve modulation of XY And and UZ Vir - Two Blazhko RR Lyrae stars with additional frequencies
Authors: A. Sódor, G. Hajdu, J. Jurcsik, B. Szeidl, K. Posztobányi, Zs. Hurta, B. Belucz, E. Kun

A thorough analysis of multicolour CCD observations of two modulated RRab-type variables, XY And and UZ Vir is presented. These Blazhko stars show relatively simple light-curve modulation with the usual multiplet structures in their Fourier spectra. One additional, independent frequency with linear-combination terms of the pulsation frequency is also detected in the residual spectrum of each of the two stars. The amplitude and phase relations of the triplet components are studied in detail. Most of the epoch-independent phase differences show a slight, systematic colour dependence, however, these trends have the opposite sign in the two stars. The mean values of the global physical parameters and their changes with Blazhko phase are determined utilizing the Inverse Photometric Method (IPM). The modulation properties and the IPM results are compared for the two variables. The pulsation period of XY And is the shortest when its pulsation amplitude is the highest, while UZ Vir has the longest pulsation period at this phase of the modulation. Despite this opposite behaviour, the phase relations of their mean-physical-parameter variations are similar. These results are not in accord with the predictions of the Blazhko model of Stothers (2006, ApJ, 652, 643).

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Blobrana


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Posts: 131433
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Title: RR Lyrae type stars, ST Boo and RR Leo: 2007 Observations and the preliminary results of the frequency analysis
Authors: Fehmi EkmekC{i}, Lale Cel{i}k, H. Volkan Senavci

We present BVR light curves of pulsating stars, ST Boo and RR Leo, obtained between March and September 2007 at the Ankara University Observatory (AUG) and the TUBITAK National Observatory (TUG). Although these observational data are insufficient to obtain the reliable results for a frequency analysis of ST Boo and RR Leo stars, in this study, we tried to investigate the pulsation phenomena of these two stars, as an overview, using the Period04 software package. As preliminary results, we present the possible frequencies for ST Boo and RR Leo.

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Blobrana


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Posts: 131433
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Blazhko Stars
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Title: How to Correctly Stitch Together Kepler Data of a Blazhko Star
Authors: L. Celik, F. Ekmekçi, J. Nemec, K. Kolenberg, J. M. Benko, R. Szabó, D. W. Kurtz, K. Kinemuchi, H. V. Senavc

One of the most challenging difficulties that precedes the frequency analysis of Kepler data for a Blazhko star is stitching together the data from different seasons (quarters). We discuss the preliminary steps in the stitching, detrending and rescaling process using the data for long-term Blazhko stars. We present the process on Kepler data of a Blazhko star with a variable Blazhko cycle and some first results of our analysis.

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Blobrana


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Posts: 131433
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RE: RR Lyrae stars
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Title: Detection of chaos in RR Lyrae models
Authors: E. Plachy, Z. Kolláth, L. Molnár

The period doubling phenomenon was recently discovered in RR Lyrae stars with the Kepler space telescope and has been theoretically explained by hydrodynamic calculations. However, peculiar solutions of the Florida-Budapest turbulent convective hydrodynamic code suggest that bifurcation cascade may evolve to chaos in these dynamical systems. We show that chaotic behaviour may be recovered from the radius variations of the model using the global flow reconstruction method. The fractal (Lyapunov) dimension of the underlying dynamical attractor is calculated to be ~2.2. Compared to the radius, the luminosity variations proved to be less suitable for such investigations due to their complexity. That suggest that even the continuous Kepler data would require transformation before conducting a similar analysis.

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Blobrana


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Title: RR Lyrae Stars, Metal-Poor Stars, and the Galaxy
Authors: Andrew McWilliam (Carnegie Observatories)

This online book contains the proceedings of a meeting on "RR Lyrae Stars, Metal-Poor Stars, and the Galaxy" held at the Carnegie Observatories, Pasadena, California, in January 2011. The purpose of the scientific meeting was to honour the 80th year of our colleague, George W. Preston III.
The book comprises the 5th volume of the Carnegie Observatories Astrophysics Series. In addition to links for each arXiv article I also include links to download the entire volume, free of charge.

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Blobrana


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Title: Atmospheres of RR Lyrae Stars: Hypersonic Shock waves, Helium line detection and Magnetic fields. A few spectra for George Preston on the occasion of his birthday
Authors: Merieme Chadid (1,2) ((1) Observatoire de la Cote d'Azur, Universit'e Nice Sophia-Antipolis, Nice, France (2) Antarctica Research Station, South Pole TAAF, Antarctica)

During intensive/comparative studies with Preston's spectroscopic works (1961, 1962, 1964 & 1965) on RR Lyrae atmospheric phenomena, I unexpectedly found the existence of hypersonic shock waves (Chadid 1996 & 2008), that are strongly connected with the turbulence amplification mechanism (Chadid 1996b) and the Blazhko modulation (1997). Here I will show how the hypersonic shocks are at the origin of helium line formation and connected with the helium emission and line doubling detected by Preston (2009, 2011).
I will present new neutral and single ionised helium line data in the hypersonic Blazhko star S Arae. The He II appears as a weak emission and its origin is strongly connected with the hypersonic shock in S Arae. The shock is extremely strong and can reach a Mach number >30. The HeI lines first appear in emission, over ~2% of the pulsation period, followed by the HeI absorption doubling phenomenon occurring simultaneously with the neutral metallic absorption line phenomenon over ~8% of the pulsation period.
Despite several claimed detections of magnetic fields in RR Lyrae, Preston (1967) found none after two years of observations. This is consistent with my recent spectro-polarimetric measurements (2004), over four years, concluding that RR Lyr is a bona fide nonmagnetic star, leading to the falsification of all the models of the Blazhko effect requiring strong photospheric magnetic fields. I report on a new series of high precision circular polarization spectroscopic observations of Blazhko star RV UMa. The longitudinal field measurements of RV UMa show a mean longitudinal magnetic field of B_l = -13±35 G, and no significant detection over the entire pulsation cycle.
These spectroscopic results reveal a serious challenge for explaining the complex behaviour in the pulsation of hypersonic atmospheres of RR Lyrae stars.

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