Ups and downs in understanding stellar variability Wrocław

Mid 1960ties. Variability of Cepheids and RR Lyrae stars explained Radial pulsation hypothesis (Ritter 1879) confirmed (Shapley 1914, Baade 1926) Difference between RR Lyrae stars and Cepheids (Baade 1946) Stars as heat engines (Eddington 1917) The  - mechanism critical role of the HeII ionization zone (Zhevakin, 1953) Overstability in realistic Cepheid models (Baker & Kippehahn, 1962, 1965) Nonlinear modeling of RR Lyrae stars and Cepheids (Christy, 1965, 1966)

Major open problems of late 1960ies 1. Convection /pulsation interaction. The red edge of the Cepheid Instability Strip (Baker & Gough, 1979) 2. Driving mechanism for nonradial oscillations in β Cephei stars proposed by Ledoux (1951) Nonadiabatic code for nonradial oscillations integrated with the stellar evolution code of Kippenhahn & Weigert. (Baker & Dziembowski, unpublished) Mixed modes in evolved MS stars, unstable in the δ Scuti T eff range but no instability in the β Cep range

Why Cepheids and RR Lyrae stars choose only radial modes ? Very strong damping of quadrupolar modes in radiative interior (WD 1971) Unstable trapped modes of moderate degrees in the vicinity of radial F and 1O modes In Cepheid ( Osaki 1977 ) and RR Lyrae ( WD 1977 ) models Are high degree modes excited in stars ? (Balona & WD 1999) Instability extends to high degree f-modes but the driving effect changes and to hotter stars ( Shibahashi &Osaki 1981 ).

Multiperiodic variability in the Cepheid Instability Strip Common among  Scuti stars, rare in RR Lyrae and Cepheids. Same driving effect but resonant vs nonresonant amplitude limitation mechanism Beyond the linear theory : amplitude equation formalism, parametric resonance (1982) Application to  Scuti stars , collaborators: M. Królikowska, A. Kosovichev) P. Moskalik (MSc 1984) M. Królikowska (PhD 1988), R. Nowakowski (PhD 2003)

Asteroseismology in the pre-CoRoT era Prospects for sounding internal rotation (1996, collaborators: M.-J. Goupil, E. Michel, P. Goode) Lost optimism - troublesome high-degree modes (1997, 2010 collaborators: L. Balona, M.-J. Goupil,J. Daszyńska-Daszkiewicz, A Pamyatnykh) Back to ground-base data. Observational mode identification ( collaborators: J. Daszyńska-Daszkiewicz, A Pamyatnykh, M. Breger, G. Houdek, W. Zima )  Scuti stars - embarras de richesse (1995 -collaboration with the DSN M. Breger, G. Handler,……. A.Pamyatnykh )

Petersen diagram and the huge mass discrepancy Double mode Cepheids (Petersen 1973) Appeal to atomic physicists for a reexamining heavy element opacities (Simon 1982) OPAL (Iglesias et al. 1992) and OP (Seaton 1992) projects The huge mass discrepancy removed (Moskalik et al. 1992)

Why some Cepheids and RR Lyrae stars choose double mode pulsation (1984, collaborator G. Kovacs) Only-F, Only 1O, and EO regions (Baker & von Sengbusch 1970, Stellingwerf 1975) The 1:2 resonance between F and 2O mode in the EO region First double mode RR Lyrae star (Jerzykiewicz & Wentzel 1977) The same resonance may also explain also the Blazkho effect in RR Lyrae stars (Moskalik 1985, PhD) Amplitude formalism for radial modes developed to cubic terms (Buchler & Kovacs 1986) support for the role of the 1:2 in double mode pulsation but Not always elegant means correct - no resonance at realistic stellar parameter. The Florida-Budapest (Kollath et al. 2002) and Warsaw (Smolec & Moskalik 2008, 2010) convective codes Maybe resonances after all

Double- and triple-mode Cepheid from OGLE survey Petersen diagrams for Magellanic Cloud Cepheids (Soszyński et al. 2008, 2010) SMC LMC Deduction of stellar parameters, search for resonances ( , collaborators: Moskalik, Smolec) Only P S /P L  0.6 could not be explained in terms of radial modes. Perhaps 1O+f l (l=42-50)

The 1:1 resonances and the Blazkho effect The amplitude equations up to cubic order for nonradial modes (Buchler & Goupil 1984,1997, Van Hoolst 1994) radial/dipolar mode coupling as the cause of Blazkho effect ( collaborators: T. Van Hoolst, S. Kawaler, S. Cassisi, R. Nowakowski, T. Mizerski) dipolar m=0 or m=  1 pair Elegant but rather unlikely solution of the problem

The opacity mechanism in the Fe-bump zone and B-type stars Not only β Cephei stars (1992 -, collaborators: P. Moskalik, A. Pamyatnykh, H. Cugier, M. Jerzykiewicz, L. Balona, G. Handler, J. Daszyńska-Daszkiewicz, W. Szewczyk) (Simon 1982, Iglesias et al. 1992, Cox et al. 1992) New data, new problems Parallel works: (Gautschy & Saio, 1993, Lee 1998, Townsend 2005, Saio et al. 2007, Miglio et al 2007) sdB stars (Charpinet et al. 1996,... )

Red giant pulsation overstability vs stochastic driving Solar oscillations - stochastic driving (Leighton et al. 1960, Ulrich 1970, Ando & Osaki, 1975, Goldreich & Keeley 1977) Mira (Fabricius 1596), - overstability, ( Ostlie & Cox 1986, Xiong et al. 1998) Many PL relations from MACHO and OGLE (the OSARGs) The best of CoRoT and KEPLER Parallel works: J. Christensen -Dalsgaard et al. 2001, Kiss & Bedding 2003, Xiong & Deng 2007, Dupret et al )  UMa, OSARGs ( collaborators D. Gough, G. Houdek, R. Sienkiewicz, I. Soszyński +, B. Mosser +) Microlensing surveys inspiread by Bohdan Paczyński

The decade of space missions and massive photometry old and new problems

Norman Baker died on October 11, 2005 Bohdan Paczyński died on April 19, 2007 Robert Christy died on October 3, 2012 Robert Buchler died on October 16, 2012 Arthur Cox died on March 12, 2013

Thank you for coming to Wrocław

The opacity mechanism in radiative and convective layers a  Sct star model

a  Dor star model