Precision Asteroseismology Proceedings IAU Symposium No. 301, 2014 (cid:13)c 2014International AstronomicalUnion J.A. Guzik, W.J. Chaplin, G. Handler & A. Pigulski, eds. DOI:00.0000/X000000000000000X Pulsating variables from the OGLE and Araucaria projects G. Pietrzyn´ski1,2 1 Warsaw University Observatory,Al. Ujazdowskie 4, 00-478 Warszawa, Poland email: [email protected] 2Departamentode Astronom´ıa, Universidad deConcepci´on, Casilla 160-C, Concepci´on, Chile Abstract. We present some results of long term studies of pulsating stars conducted in the 4 course of the OGLE and Araucaria projects. In particular very scarce eclipsing binaries con- 1 taining pulsating stars are discussed. Such systems provide a unique opportunity to improve 0 2 calibration of the cosmic distance scale and to bettercalibrate stellar evolutionary models. l u J 1. OGLE and ARAUCARIA projects 6 Optical Gravitational Lensing Experiment (OGLE) is one of the biggest astronomical ] surveys. This project has been in operation over the last 21 years. With the current R instrumental setup, the OGLE team is capable to observe about one billion stars ev- S ery night. The observations are mainly conducted in the Milky Way (bulge and disc) . h and Magellanic Clouds. Based on the collected data, an enormous amount of precise p light curves for basically all kinds of pulsating stars were already published: Cepheids - o (Soszyn´skietal.2008,2010a),RRLyrae(Soszyn´skietal.2010b,2011a),longperiodvari- r ables (Soszyn´ski et al. 2011b, 2013), etc., and several new catalogs are in preparation. t s Thanks to an exquisite statistics and high quality of the data, many extremely scarce a and very interesting objects have been also discovered, including very good candidates [ forpulsatingstarsineclipsingbinarysystems(Soszyn´skietal.2008,2011a)andaunique 2 sample of eclipsing binary systems composed of clump giants (Graczyk et al. 2011). v Araucaria project.Themaingoalofthisprojectistosignificantlyimprovethecalibra- 5 3 tion of the cosmic distance scale based on observations of several distance indicators in 3 nearby galaxies. As a first step, we performed an optical survey of nine nearby galaxies 0 discovering about 700 Cepheids (Pietrzyn´ski et al. 2002, 2004, 2006, 2007, 2010a). We . 1 also performed infrared observations of discovered Cepheids (Gieren et al. 2005b, 2006, 0 2009,2013;Pietrzyn´skietal.2006),andRRLyraestarsselectedfromtheOGLEcatalogs 4 in the LMC, SMC and Sculptor galaxies (Pietrzyn´ski et al. 2008, Szewczyk et al. 2008, 1 2009). Recently, a very important part of the Araucaria project is related to detailed : v studies of eclipsing binary systems discovered by the OGLE project, which have very Xi large potential for precise and accurate distance determination and also for improving our knowledge of basic physics of pulsating stars. During my talk I will focus on some r a results obtained for some of these systems. 2. Setting the zero point for P-L relation of pulsating stars The distance to the LMC is widely adopted as the zero point in the calibration of the cosmic distance scale. Therefore, a precise and accurate distance determination to this galaxy is paramount for astrophysics in general. Detached eclipsing double-lined spectroscopic binaries offer a unique opportunity to 1 2 G. Pietrzyn´ski measuredistances directly(e.g.KruszewskiandSemeniuk 1999).Recently,we measured distance to the LMC with 2% precision, based on the analysis of eclipsing binary sys- tems composed of red clump giants (Pietrzyn´ski et al. 2013). For eight such systems linear sizes of both components were measured with 1% accuracy based on modeling of high-quality photometric light curves obtained by the OGLE projectand radialvelocity curves constructed by the Araucaria team. Having first ever discovered late-type eclips- ing binaries (G type), we used a well calibrated relationship between angular diameter and V −K color (Di Benedetto 2005,Kervella et al. 2004)and measured corresponding angular sizes of the components of our systems with an accuracy of 2%. As the result weobtainedthe mostaccurateandreliableLMC distance,whichprovidesa strongbasis for the determination of the Hubble constantwith an accuracyof about 3%.At present, we are working on improving the surface brightness-colorcalibration and measuring the LMC distance with an accuracy of 1%. Since the OGLE group constructed outstanding period-luminosity (P-L) relations for severaldifferentpulsatingstarsintheLargeMagellanicCloud(e.g.Soszyn´skietal.2010a, 2011b, 2013), our distance determination provides also an opportunity to calibrate uni- form fiducial P-L relations for basically all P-L relations of pulsating stars used for distance determination. 3. Cepheids in eclipsing binaries TheOGLEprojectprovidedalsoverygoodcandidatesforclassicalCepheidsineclips- ing systems (e.g. Soszyn´ski et al. 2008). Such systems provide a unique opportunity to measure precisely and accurately stellar parameters of Cepheids. In consequence, they provide very strong constraints on stellar evolutionary and pulsation models. One can also measure distances to such targets using three independent techniques: P-L relation, Baade-Wesselink method, and eclipsing binaries described above. Comparing the inde- pendentdistances,the potentialsystematicerrorsassociatedwitheachofthese methods canbepreciselytracedout.Becauseofthe hugepotentialofthesesystemsforimproving our capability of measuring distances with classical Cepheids and to better understand basic physics of these stars, as a part of the Araucaria project we started a long-term program to characterize them. In 2010 we confirmed that one of the OGLE candidates —OGLE-LMC-CEP-227— is indeed aphysicalsystemcontaininga Cepheid. Basedon high-quality data, we measured the dynamical mass of the Cepheid with an accuracy of 1% (Pietrzyn´ski et al. 2010b). Recently, we significantly improved the accuracy of determinationofthe physicalparametersofthissystemandmeasureddirectlythepfac- tor for the Cepheid (Pilecki et al. 2013). This analysis complements our previous study on the calibration of the p factor (Gieren et al. 2005a, Nardetto et al. 2011, Storm et al. 2011). Pietrzyn´ski et al. (2011) measured the dynamical mass of another Cepheid in aneclipsingsystemwithsimilaraccuracy.Theseresultsalreadytriggeredseveraltheoret- icalinvestigations(Cassisi& Salaris2011,Neilson et al.2011,PradaMoroniet al. 2012, Marconi et al. 2013). Unfortunately, there are no Cepheids in eclipsing binary systems known so far in the Milky Way. However, some of the Cepheids in binary systems are sufficiently close to observe them interferometrically (Gallenne et al. 2013). Combining spectroscopic and interferometric data one should be also able to precisely measure distances, masses and other physical parameters for several Cepheids in the Milky Way (Gallenne et al. 2013; see also Gallenne et al., these proceedings). 3 4. Binary Evolution Pulsating stars After many years of intense searching for an RR Lyrae star in an eclipsing binary systemaverygoodcandidate,OGLE-BLG-RRLYR-02792,wasdiscoveredbytheOGLE team (Soszyn´ski et al. 2010b). Together with high resolution spectra obtained by the Araucaria team, we modeled this system and determined its physical parameters. Sur- prisingly, the mass of the primary component, pulsating star classified as an RR Lyrae starbasedonpropertiesofitslightcurve,turnedouttobe0.261±0.015M⊙(Pietrzyn´ski et al. 2012). This is of course incompatible with the theoretical predictions for a classi- cal horizontal branch star evolving through the instability strip. However,the relatively shortorbitalperiodofthissystem(15.24days)suggeststhatmassexchangebetweenthe components should have occurred during its evolution. Inspired by this possibility, we calculated a series of models for Algol systems and found that a system which initially contained two stars with masses M1 = 1.4M⊙ and M2 =0.8M⊙orbitingeachotherwithaninitialperiodof2.9dayswould,after5.4Gyrof evolution,haveexchangedmassbetweenthecomponentsasclassicalAlgolsdo,andtoday would form a system very similar to RRLYR-02792 (e.g. with M1 = 0.268M⊙, M2 = 1.665M⊙, and Porb = 15.9 days). We therefore conclude that the primary component of our observed system is not a classical RR Lyrae star with its well-known internal structure, but rather a star which possesses a partially degenerated helium core and a small hydrogen-rich envelope (shell burning). The primary component has lost most of its envelope to the secondary during the red giant branch phase due to the mass exchange in a binary system, and is now crossing the main instability strip during its evolutiontowardsthe hot subdwarfregionof the H-R diagram(Pietrzyn´skiet al. 2012). Pulsationalproperties of this starwere investigatedby Smolec et al. (2013). As a result, wediscoveredanewevolutionarychannelofproducingbinaryevolutionpulsating(BEP) stars—new inhabitantsofthe classicalinstability strip.They mimic classicalRRLyrae variables,buthaveacompletelydifferentorigin.Sincethe primarycomponentscanhave verydifferentmassesduringthemassexchange,theycanbeexpectedindifferentregions of the instability strip. Very recently, Maxted et al. (2013) discoveredanother BEP star crossing the instability strip of δ Scuti stars. 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