Communications in Asteroseismology Volume 145 June, 2004 Proceedings of the JENAM Minisymposium Budapest, 29-30 August, 2003 Edited by Zoltan Kollath & Gerald Handler Editor: Michel Breger, TurkÄ enschanzstra¼e 17, A - 1180 Wien, Austria Layout and Production: Wolfgang Zima Editorial Board: Gerald Handler, Don Kurtz, Jaymie Matthews, Ennio Poretti Publication Board: Victoria Antoci http://www.deltascuti.net British Library Cataloguing in Publication data. A Catalogue record for this book is available from the British Library. All rights reserved ISBN 3-7001-3291-3 ISSN 1021-2043 Copyright °c 2004 by Austrian Academy of Sciences Vienna Contents Preface 5 Identi¯cation of modes in main-sequence pulsators by means of multi-color photometry by J. Daszynsk¶ a-Daszkiewicz, W.A. Dziembowski, A.A. Pamyatnykh 6 Influence of the convective flux perturbation on stellar oscillations: application to ± Scuti and γ Doradus stars by A. Grigahc`ene, M-A. Dupret, R. Garrido, M. Gabriel and R. Scuflaire 9 Testing the internal physics of white dwarfs from their pulsational properties by J. Isern, E. Garc¶³a{Berro, A.H. C¶orsico, O.G. Benvenuto and L.G. Althaus 12 The Blazhko E®ect: Facts, Figures and Future work by K. Kolenberg 15 Numerical modelling of the RR Lyrae instability strip by R. Szab¶o 20 UBV I Time-series Photometry of the Old LMC Globular Cluster Reticulum by V. Ripepi, M. Monelli, M. Dall'Ora et al. 23 Long-term photometric study of LBVs in M33 by A. Zharova and O. Sholukhova 26 Cepheids in binary systems { new candidates in the Magellanic Clouds by L. Szabados 27 A continuous population of variable stars up to about 1.5 mag above the horizontal branch? by L. Baldacci, G. Clementini, E.V. Held, M. Marconi, L. Rizzi 30 The core/envelope asymmetry in p-mode pulsating stars by A. Miglio and E. Antonello 35 Mapping non-radial pulsation using surface imaging techniques by S.V. Berdyugina, H. Korhonen, J.H. Telting, C. Schrijvers 38 High Amplitude ± Sct-type variables by E. Rodr¶³guez 40 Pulsational behaviour of the HADS RY Lep by E. Rodr¶³guez, C.D. Laney, P.J. Amado, M.J. L¶opez-Gonz¶alez and M. Joner 46 SZ Lyn: New pulsational and orbital elements based on old and recent photometric observations by K.D. Gazeas, P.G. Niarchos, K.A. Boutsia 47 Short{Period Variables in ASAS Photometry by J. Molenda{Zak_ owicz 48 Asteroseismology of Procyon: Preliminary results from SARG by R.U. Claudi, A. Bonanno, R. Ventura et al. 51 The use of Petersen diagrams and period ratios in investigating the pulsational content of stars in the classical Instability Strip by E. Poretti and M. Beltrame 53 4 Period{radius relation for semiregular and Mira stars by K. Szatm¶ary 58 Relevant issues in the study of Pre-Main Sequence ± Scuti stars by M. Marconi, V. Ripepi, F. Palla and A. Ruoppo 59 Pulsating stars in open clusters by T. Arentoft, L.M Freyhammer, M.Y Bouzid, C. Sterken and S. Frandsen 65 A Variable Star Survey of the Open Cluster NGC 2126 by A. G¶asp¶ar, L. L. Kiss, A. Derekas et al. 68 Amplitude and frequency variability of pulsating stars by G. Handler 69 New observational results on pulsating B stars by A. Pigulski 72 Radial Velocity variations of the roAp-star HD122970: new results by A. Gamarova, A.P. Hatzes and D. Mkrtichian 77 Pulsation and Binarity in RZ Cas by E. Rodr¶³guez, J.M. Garc¶³a, D.E. Mkrtichian et al. 78 AB Cas revisited by E. Rodr¶³guez, P.J. Amado, J.M. Garc¶³a, V. Costa and M.J. L¶opez-Gonz¶alez 81 A few concluding remarks by A. Baglin 82 Comm. in Asteroseismology Vol. 145, 2004 Preface Asteroseismology is a young branch of stellar astrophysics in two ways: ¯rstly, the methods to sound stellar interiors have only recently - and are still being - developed and secondly, many researchers in this ¯eld are young people. The 12th JENAM conference has been organised with some main aims being the interaction between young and experienced scientists, and to increase the possibilities for young astronomers to ¯nd employment. In this spirit, a job market for these people was also o®ered for the ¯rst time. Consequently, it was only logical that a two-day asteroseismology mini-workshop, focus- ing on the impact of such studies on aspects of stellar evolution, was also held during the JENAM meeting in Budapest. Moreover, given the focus on communication and contents of the workshop there is no journal other than Communications in Asteroseismology more appropriate for publishing its proceedings. In the following, you will ¯nd a summary of the presentations given at this workshop, with reviews by several selected world specialists in asteroseismology and stellar evolution, but also by young researchers, supplemented by a number of poster presentations, all of which will give you a broad overview of the recent status of research and highly interesting outlooks into the future. The scienti¯c organising committee of the 'Asteroseismology and Stellar Evolution' min- isymposium consisted of the following people: Gerald Handler (Vienna/Austria) Hans Kjeldsen (Aarhus/Denmark) Zolt¶an Koll¶ath (Budapest, Hungary, convenor) Margit Papar¶o (Budapest/Hungary) Ennio Poretti (Merate/Italy) Chris Sterken (Brussels/Belgium) The minisymposium was sponsored by the organizers of JENAM 2003: European Astro- nomical Society, Konkoly Observatory, Roland EÄotvÄos Physical Society and EÄotvÄos Lor¶and University. The Editors Comm. in Asteroseismology Vol. 145, 2004 Identi¯cation of modes in main-sequence pulsators by means of multi-color photometry J. Daszynsk¶ a-Daszkiewicz1;2, W.A. Dziembowski3;4, A.A. Pamyatnykh4;5;6 1 Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium 2 Astronomical Institute of the WrocÃlaw University, ul. Kopernika 11, 51-622 WrocÃlaw, Poland 3 Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland 4 Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland 5 Institute of Astronomy, Russian Academy of Science, Pyatnitskaya Str. 48, 109017 Moscow, Russia 6 Institute of Astronomy, University of Vienna, TurkÄ enschanzstr. 17, A-1180, Vienna, Austria Abstract We discuss two problems connected with the application of the method of photometric am- plitudes and phases for mode identi¯cation. The ¯rst one concerns the e®ect of rotational mode coupling in ¯ Cep models. The second one deals with the strong dependence of the photometric observables on convection in ± Scuti stars. Introduction Oscillation spectra of main-sequence pulsators, like ¯ Cep and ± Sct stars, only seldom exhibit equidistant patters, which are typical, for example, in white dwarfs. Therefore, it is di±cult to identify oscillation modes from frequency spectra alone. The most popular method of mode identi¯cation is based on multicolor photometry (Balona & Stobie 1979, Watson 1988). We address here two problems concerning this method which have been discussed in details in two of our recent papers (Daszynsk¶ a-Daszkiewicz et al. 2002, 2003). Photometric amplitudes and phases in rotating ¯ Cep models If e®ects of rotation are negligible, the photometric diagnostic diagrams (amplitude ratio vs. phase di®erence) are independent of the inclination angle, i, and of the azimuthal order, m, and they may reveal the spherical harmonic degree, `. For ¯ Cep star models, oscillation modes are located in the diagnostic diagrams in very well separated regions of di®erent values of `. With the results of linear nonadiabatic theory these diagrams have been successfully applied to many stars (Cugier et al. 1994). However amongst ¯ Cep stars we meet quite often fast rotators. The most important e®ect of moderate rotation is mode coupling. It occurs if the frequency di®erence between modes j and k is of the order of the angular velocity of rotation, !j ¡ !k » ­, and if the spherical harmonic indices satisfy the relations: `j = `k §2 and mj = mk. For eigenfunctions of coupled modes one has to consider superpositions of all modes satisfying the conditions mentioned above. The complex amplitude of the monochromatic flux variation for a coupled mode is expressed as A¸(i) = akA¸;k(i) Xk J. Daszynsk¶ a-Daszkiewicz, W.A. Dziembowski, A.A. Pamyatnykh 7 " " 2.5 '=0 2.5 '=2 0 0 2.0 2.0 y A / u A a = 0.85 a = 0.53 1.5 11 12 1.5 a = 0.58 a = -0.82 1 1 21 22 3 3 2 2 1.0 4 1.0 4 0.5 0.5 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 ϕ - ϕ [rad] ϕ ϕ [rad] u y u - y Figure 1: Two mode coupling between ` = 0; p1 and ` = 2; g1 with the dimensionless frequency distant ¢σ = 0:003, in the model at log Teff = 4:374 and Vrot = 100 km/s. Arrows point the polar direction. where ak are solutions of the degenerate perturbation theory for slowly rotating stars (Sou¯ et al. 1998). These quantities describe contributions of kth- spherical harmonic to the coupled mode. A¸;k is the complex amplitude for single-` mode. Now the amplitude ratios and phase di®erences become both i and m dependent. In Fig.1 we give an example of coupling between a close ` = 0 and 2 pair at an equatorial velocity of about 100 km/s. Open circles mark positions of single ` modes in the diagram based on u and y StrÄomgren passbands. In the left panel, we see the nominal ` = 0 mode. It is indeed dominated by the ` = 0 component, but there is a considerable ` = 2 component. Small dots are equally spaced in cos i, therefore their density reflects the probability of the situation.