* Astronomy

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RE: RR Lyrae stars

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Title: RR Lyrae the Stellar Beacons of the Galactic Structure
Authors: Giuseppe Bono (1,2), Massimo Dall'Ora (3), Filippina Caputo (2), Giuseppina Coppola (3), Katia Giovenali (1), Marcella Marconi (3), Anna Marina Piersimoni (4), Robert F. Stellingwerf (5) ((1) Universit'a di Roma Tor Vergata, Roma, Italy, (2) INAF-Osservatorio Astronomico di Roma, Italy, (3) INAF-Oservatorio Astronomico di Capodimonte, Napoli, Italy, (4) INAF-Oservatorio Astronomico di Collurania, Teramo, Italy, (5) Stellingwerf Consulting, AL, USA)

We present some recent findings concerning the use of RR Lyrae as distance indicators and stellar tracers. We outline pros and cons of field and cluster RR Lyrae stars and discuss recent theoretical findings concerning the use of the Bailey (amplitude vs pulsation period) diagram to constrain the possible occurrence of Helium enhanced RR Lyrae stars. Nonlinear, convective RR Lyrae models indicate that the pulsation properties of RR Lyrae stars are minimally affected by the helium content. The main difference between canonical and He enhanced models is due to the increase in luminosity predicted by evolutionary models. Moreover, we focus our attention on the near-infrared Period-Luminosity (PL) relation of RR Lyrae and summarize observational evidence concerning the slope of the K-band PL relation in a few globulars (M92, Reticulum, M5, Omega Cen) covering a range in metallicity of ~1 dex. Current findings suggest that the slope has a mild dependence on the metal content when moving from the metal-poor to the metal-intermediate regime.
Finally, we also discuss the use of RR Lyrae stars either to estimate (helium indicator: A-parameter) or to measure (absorption and emission lines) the helium content.

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Title: RR Lyrae Research with the Kepler Mission
Authors: K. Kinemuchi

The Kepler Mission is a Discovery mission supported by NASA's Science Mission Directorate, and its primary aim is to discover Earth-sized planets in the habitable zone of solar-type stars. The space telescope was designed with a photometer that monitors the Kepler field in a near continuous manner in order to achieve this goal. With this mission, the asteroseismology community also benefits from the Kepler data via the abundant time-series photometry. With a short cadence of 1 minute and long cadence of 30 minute observations, the time coverage for many variable stars is unprecedentedly complete. The Kepler field also contains the archetype RR Lyr, and the Kepler Asteroseismic Science Consortium (KASC) Working Group for RR Lyrae stars have been working to uncover the mysteries surrounding these stars. I will provide an overview of the Kepler program in relation to RR Lyrae research.

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Title: CoRoT light curves of RR Lyrae stars. CoRoT 101128793: long-term changes in the Blazhko effect and excitation of additional modes
Authors: Ennio Poretti, Margit Paparo, Magali Deleuil, Merieme Chadid, Katrien Kolenberg, Robert Szabo, Jozsef M. Benko, Eric Chapellier, Elisabeth Guggenberger, Jean-Francois Le Borgne, Florent Rostagni, Herve Trinquet, Michel Auvergne, Annie Baglin, Luis M. Sarro, Werner W. Weiss

The CoRoT (Convection, Rotation and planetary Transits) space mission provides a valuable opportunity to monitor stars with uninterrupted time sampling for up to 150 days at a time. The study of RR Lyrae stars, performed in the framework of the Additional Programmes belonging to the exoplanetary field, will particularly benefit from such dense, long-duration monitoring. The Blazhko effect in RR Lyrae stars is a long-standing, unsolved problem of stellar astrophysics. We used the CoRoT data of the new RR Lyrae variable CoRoT 101128793 (f0=2.119 c/d, P=0.4719296 d) to provide us with more detailed observational facts to understand the physical process behind the phenomenon. The CoRoT data were corrected for one jump and the long-term drift. We applied different period-finding techniques to the corrected timeseries to investigate amplitude and phase modulation. We detected 79 frequencies in the light curve of CoRoT 101128793. They have been identified as the main frequency f0, and its harmonics, two independent terms, the terms related to the Blazhko frequency, and several combination terms. A Blazhko frequency fB=0.056 c/d and a triplet structure around the fundamental radial mode and harmonics were detected, as well as a long-term variability of the Blazhko modulation. Indeed, the amplitude of the main oscillation is decreasing along the CoRoT survey. The Blazhko modulation is one of the smallest observed in RR Lyrae stars. Moreover, the additional modes f1=3.630 and f2=3.159 c/d are detected. Taking its ratio with the fundamental radial mode into account, the term f1 could be the identified as the second radial overtone. Detecting of these modes in horizontal branch stars is a new result obtained by CoRoT.

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Title: First Kepler results on RR Lyrae stars
Authors: K. Kolenberg, R. Szabó, D. W. Kurtz, R. L. Gilliland, J. Christensen-Dalsgaard, H. Kjeldsen, T. M. Brown, J. M. Benkö, M. Chadid, A. Derekas, M. Di Criscienzo, E. Guggenberger, K. Kinemuchi, A. Kunder, Z. Kolláth, G. Kopacki, P. Moskalik, J. M. Nemec, J. Nuspl, R. Silvotti, M. D. Suran, W. J. Borucki, D. Koch, J. M. Jenkins

We present the first results of our analyses of selected RR Lyrae stars for which data have been obtained by the Kepler Mission. As expected, we find a significant fraction of the RRab stars to show the Blazhko effect, a still unexplained phenomenon that manifests itself as periodic amplitude and phase modulations of the light curve, on time scales of typically tens to hundreds of days. The long time span of the Kepler Mission of 3.5 yrs, and the unprecedentedly high precision of its data provide a unique opportunity for the study of RR Lyrae stars.
Using data of a modulated star observed in the first roll as a showcase, we discuss the data, our analyses, findings, and their implications for our understanding of RR Lyrae stars and the Blazhko effect. With at least 40% of the RR Lyrae stars in our sample showing modulation, we confirm the high incidence rate that was only found in recent high-precision studies. Moreover, we report the occurrence of additional frequencies, beyond the main pulsation mode and its modulation components. Their half-integer ratio to the main frequency is reminiscent of a period doubling effect caused by resonances, observed for the first time in RR Lyrae stars.

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Title: RR Lyrae Pulsation Theory
Authors: Marcella Marconi

RR Lyrae stars play an important role as distance indicators and stellar population tracers. In this context the construction of accurate pulsation models is crucial to understand the observed properties and to constrain the intrinsic stellar parameters of these pulsators. The physical mechanism driving pulsation in RR Lyrae stars has been known since the middle of the 20th century and many efforts have been performed during the last few decades in the construction of more and more refined pulsation models. In particular, nonlinear pulsation models including a nonlocal time-dependent treatment of convection, such as the ones originally developed in Los Alamos in the seventies, allow us to reproduce all the relevant observables of radial pulsation and to establish accurate relations and methods to constrain the intrinsic stellar properties and the distance of these variables. The most recent results on RR Lyrae pulsation obtained through these kinds of models will be presented and a few still debated problems will be discussed.

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RR Lyraes

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RR Lyrae stars