We briefly review the results obtained by using the times of maximum brightness of RR Lyrae variables. They cover more than 120 years and have been used to study the evolutionary changes of the pulsational periods, the different shapes of the Blazhko effect among Galactic RRab stars, and the interplay between pulsational and Blazhko periods in the eponym of the class, RR Lyr. The data are stored in the GEOS database, continuously fed by contributions from professional and amateur astronomers. <P /

Audejean, M.

Hirosawa, K.

Klotz, A.

Le Borgne, J. -F.

PORETTI, Ennio

arXiv

OA@INAF - Istituto Nazionale di Astrofisica

2016Publication Year2020-05-26T15:05:40ZAcceptance in OA@INAFThe magnificent past of RR Lyrae variablesTitlePORETTI, Ennio; Le Borgne, J. -F.; Klotz, A.; Audejean, M.; Hirosawa, K.Authorshttp://hdl.handle.net/20.500.12386/25191HandleCOMMUNICATIONS FROM THE KONKOLY OBSERVATORY OF THE HUNGARIAN ACADEMY OF SCIENCESSeries105NumberarXiv:1601.02772v1  [astro-ph.SR]  12 Jan 2016RRL2015 – High-Precision Studies of RR Lyrae StarsL. Szabados, R. Szabó, K. Kinemuchi (Eds.) 2016The magnificent past of RR Lyrae variablesEnnio Poretti1,2,3,4, Jean-Francois Le Borgne2,3,4, Alain Klotz2,3,4,Maurice Audejean5 & Kenji Hirosawa61INAF-Osservatorio Astronomico di Brera, Merate (LC), Italy2Université de Toulouse, UPS-OMP, IRAP, Toulouse, France3CNRS, IRAP, Toulouse, France4GEOS, Groupe Européen d’Observations Stellaires, France5Observatoire de Chinon, Astronomie en Chinonais, Chinon, France6Variable Star Observers League(VSOLJ), Matsushiro, JapanAbstract. We briefly review the results obtained by using the times of maxi-mum brigthness of RR Lyr variables. They cover more than 120 years and havebeen used to study the evolutionary changes of the pulsational periods, the dif-ferent shapes of the Blazhko effect among galactic RRab stars, and the interplaybetween pulsational and Blazhko periods in the eponym of the class, RR Lyr.The data are stored in the GEOS database, continuously fed by contributionsfrom professional and amateur astronomers.1. IntroductionThe history of the observations of RR Lyr variables started in the XIXth century,more than 120 years ago. The variability of RR Lyr itself was discovered onthe photographic plates of the Henry Draper Memorial by Mrs. Williamina P.Fleming (Pickering et al. 1901). The first measurement comes back to July 20,1899, the first time of maximum brightness (Tmax) to September 23, 1899. Thelist of Tmax recorded from 1906 July 15 to August 25 on RW Dra clearly showsvariations of amplitude and phase (Blazhko 1907). Shapley (1916) noted thesame variations in the data of RR Lyr itself: this phenomenon was later namedBlazkho effect in the astronomical literature.The very long time baseline of available data combined with the short pe-riod of RR Lyrae variables offer an unique opportunity to look at their past as atreasure of valuable information. At this purpose, the amateur/professional asso-ciation Groupe Européen d’Observations Stellaires (GEOS) has built a databaseaimed to gather all the published Tmax values (Le Borgne et al. 2007). It alsopromotes the regular monitoring of RR Lyrae variables by means of own-madeinstruments and observing time at robotic telescopes.2. Evolutionary changesThe long time baseline allowed us the opportunity to study period changes dueto stellar evolution (Le Borgne et al. 2007). Most of the 123 scrutinized RRabstars does not show any significant period variation. This reflects the fact that12 Szabados, Szabó & KinemuchiFigure 1. Distribution of the rates of period changes. The extreme positivevalue is that of SV Erithe rapid evolution is confined in short evolutionary phases. Notwithstandingthis, we could put in evidence period increases in 27 stars and decreases in21 ones (Fig. 1). The median values of the rates are +0.14 d M yr−1 and–0.20 d M yr−1, respectively. The order of magnitude of these rates is thatexpected from evolutionary models and being common to a large number ofstars it strongly supports the evolutionary origin.We used stars not showing the Blazhko effect to study the evolutionarychanges. Or, at least, not showing an appreciable effect for the ground-basedobservations. Indeed, nowadays space-based time series are detecting very smallBlazhko effects, as in the case of V350 Lyr (Benkö & Szabó 2015). Even ifpresent in our sample, these small effects are not able to mask the large am-plitude evolutionary changes. Several case of erratic changes were observed,both increasing and decreasing the period. They should be the result of par-ticular temporary instabilities rather than be considered as representative of aparticular evolutionary stage. It was also noticed a slight excess of RR Lyr starsshowing period decreases (i.e., stars on blueward evolutionary tracks). However,further studies on a larger sample suggested that the excess was mainly due tothe limited statistics (Vandenbroere et al. 2014).3. The different shapes of the Blazhko effectWe used the GEOS database to study the Blazhko effect of galactic RRab stars,too (Le Borgne et al. 2012). The closed curves representing the Blazhko effectare constructed by plotting the magnitudes at maximum (Vmax) vs. the O − C(observed minus calculated) Tmax values. We could emphasize some clear obser-vational facts: i) the same value of the Blazhko period is observed at differentvalues of the pulsation periods; ii) different values of the Blazhko periods areobserved at the same value of the pulsation period; iii) the closed curves de-scribing the Blazhko cycles have different shapes. These curves have often theRRL2015 Conf. Papers 3Figure 2. The full rotation of the axis in stars running counterclockwise theclosed curves in the O-C (abscissa, in days) vs. Vmax (ordinate) plots.shape of a potato, but other exotic contours are observed; iv) both clockwiseand counterclockwise are possible for closed curves with similar shapes.All these facts lead to a variegate group of behaviours. For instance, thebrightest maximum could correspond to the most negative phase shift in somestars and to the most positive one in others. We could observe a full rotationof the Blazhko potato in the sample of galactic RRab stars. Figure 2 shows thecase of stars running counterclockwise. The regular survey of RRab stars is un-dergoing using both amateurs’ observatories and the robotic TAROT telescopes(Klotz et al. 2008, 2009; Le Borgne et al. 2012).4. The vanishing of the Blazhko effect of RR LyrThe analysis of the Tmax epochs listed in the GEOS database allowed us to recon-struct the changes in the pulsational period of RR Lyr. We could establish theexistence of two states characterized by the pulsation over a “long” period (longerthan 0.56684 d) and over a “short” one (shorter than 0.56682 d). We also de-termined the Blazhko period in several time intervals since 1910 and we verifiedhow it changed while the two states alternated. The variations of the pulsationand Blazhko periods resulted completely decoupled, since the Blazhko periodhad just one sudden decrease from 40.8 d to 39.0 d in 1975 (Le Borgne et al.2014). The current period is the shortest never measured, i.e., less than 0.5668 d.Some years ago, two of us (J.F. Le Borgne and A. Klotz) planned andrealized small, autonomous and transportable photometric instruments to makethe ground-based survey of RR Lyr as effective as possible. They assembled4 Szabados, Szabó & KinemuchiFigure 3. O-C values of RR Lyr folded with the Blazhko perioda commercial equatorial mount (Sky-Watcher HEQ5 Pro Goto), an AUDINECCD camera (512x768 kaf400 chip) and a photographic 135-mm focal, f/2.8lens with a field of view of 2◦ x 3◦. They gave them the nickname VTTs for“Very Tiny Telescopes”. The regular recording of the Tmax’s of RR Lyr startedin 2008. Data from VTTs and Kepler have been extensively used to recordthe monotonic long-term decrease in the amplitude of the Blazhko effect. As amatter of fact, the Blazhko effect was hard to detect by looking at the maximacollected in 2014 only. However, the new Tmax collected with the VTTs in 2015seem to show a slight increase in the amplitude of the O-C values (Fig. 3), asign that the still unknown Blazhko mechanism is back at work.Acknowledgments. The projects exploiting the GEOS database havebeen developed during some visits of E. Poretti at the Institut de Rechercheen Astrophysique et Planétologie in Toulouse. Supports from this Institute aregratefully acknowledged.ReferencesBenkö, J.M., & Szabó, R. 2015, ApJ, 809, L19Blazhko, S. 1907, AN, 175, 325Klotz, A., Boër, M., Atteia, J. L., & Gendre, B. 2009, AJ, 137, 4100Klotz, A., Vachier, F., & Boër, M. 2008, Astron. Nachr., 329, 275Le Borgne, J.F., Klotz, A., Poretti, E., et al. 2012, AJ, 144, 39Le Borgne, J.F., Paschke, A., Vandenbroere, J., et al. 2007, A&A, 476, 307Le Borgne, J.F., Poretti, E., Klotz, A., et al. 2014, MNRAS, 441, 1435Pickering, E. C., Colson, H. R., Fleming, W. P., Wells, L. D. 1901, ApJ, 13, 226Shapley, H. 1916, ApJ, 43, 217Vandenbroere, J., Le Borgne, J.F., Boninsegna, R. 2014, Geos Circular RR53

The magnificent past of RR Lyrae variables

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The magnificent past of RR Lyrae variables

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