Nonlinear Phenomena in Stellar Variability, 1993

The nonlinear theory of oscillating systems brings new aspects into the study of variable stars. Beyond the comparison of linear periods and the estimate of stability, the appearance and disappearance of possible modes can be studied in detail. While nonlinearity in stellar pulsations is not a very complicated concept, it generally requires extensive and sometimes so­ phisticated numerical studies. Therefore, the development of appropriate computational tools is required for applications of nonlinear theory to real phenomena in variable stars. Taking trends in variable star studies into consideration, the International Astronomical Union organized a colloquium for the nonlinear phenomena of variable stars at Mito, Japan in 1992. The colloquium served to give an overview of the new frontiers of variable star studies and to encourage further development of this field. The colloquium covered the fundamental theory, interesting observational facts, and the numerical modeling. The publication of the proceedings was somewhat delayed since one of the editors, M. T., was overwhelmed by administrative work. We are sorry that the excellent reviews of Drs. H. :Mori, M. Sano, and K. Makishima cannot be found in the proceedings. We also miss the summary given by Dr. W. W. Dziembowski. Throughout the editing procedure Dr. Y. Tanaka of Ibaraki University kindly helped us. Because of the unfortunate delay of the publication~ the significance of several papers may be affected. Even so, we believe that the papers are useful to variable star researchers because of their scientific importance.

A Dynamical Systems Approach to Nonlinear Stellar Pulsations.- Patterns of Aperiodic Pulsation.- Characterisation of the Dynamics of a Variable Star.- An Overview of Stellar Pulsation Theory.- Nonlinear Oscillations and Beats in the Beta Canis Majoris Stars.- One Zone Modeling of Irregular Variability of Stellar Convective Envelope.- Accretion Disk Instabilities.- Motion of a Charged Particle around a Black Hole Permeated by Magnetic Field and Its Chaotic Characters.- Nonlinear Expansion Triggered by Magnetic Stress in Accretion Flow onto a Black Hole.- Variability of X-Ray Emission from Cen X-3 Observed with Ginga.- Spatial Pattern Formation of Interstellar Medium.- Supergiant Variables: Recent Observational Results.- The Aavso Database of Variable Star Observations.- Theoretical Modes Fitting on Miras Light Curves.- On the Observed Complexity of Chaotic Stellar Pulsation.- Predicting Variable Star Light Curves.- Chaotic Behavior and Statistical Analysis of Some Mira and SR Stars.- Understanding Changes in Period Ratios.- On the Application of Fourier Decomposition Parameters.- Line-Profiles of F Supergiant Stars as Candidates of Proto-Planetary Nebulae.- Low Amplitude New Type Variable Stars in Globular Clusters.- Stellar Pulsation: (I) Analysis of Stability of Envelope.- Stellar Pulsation: (II) Multiple Distinct Shells.- Long-Term Amplitude and Period Variations of Delta Scuti Stars: A Sign of Chaos?.- The Delta Scuti Star GX Pegasi: A Theoretical Investigation of Its Power Spectrum.- Short-Term Amplitude Variation of FM Com (=HR 4684).- Period Variations and Evolution of Delta Scuti Variables.- Physical Characters of HD 93044.- Period Analysis of the Delta Scuti Star HD 93044.- Observation of a Variable, ZZ Ceti White Dwarf: GD 154.- Observation and Statistical Analysis of ZZ Piscium.- Nonlinear, Nonradial Pulsation in Rapidly Oscillating Ap Stars.- Period Variation of BW Vul.- Nonradial Oscillations in Zeta Ophiuchi in 1991.- The Onset of Quasi-Periodic Variations in Be Stars.- Optical Observations of FY Persei.- Some Insights into Stellar Structure from Nonlinear Pulsations.- Capabilities of the Optical Monitor for the Research in X-Ray Source and Stellar Variability.- Wind Variability of Lbv Stars.- Variability in Active Galactic Nuclei.- Fourier Analysis of the Hydrodynamic Limit-Cycle Models of Pulsating Stars.- Bifurcation in Hydrodynamic Models of Stellar Pulsation.- Double-Mode Stellar Pulsation.- Period Doubling with Hysteresis in BL Her-Type Models.- Nonlinear RR Lyrae Models with New Livermore Opacities.- A Linear and Nonlinear Study of Mira.- Radial and Nonradial Periods and Growth Rates of an AI Velorum Model.- The Importance of Radiative Transfer in Stellar Pulsation Models.- Hydrodynamics and Multi-Level Non-Lte Radiative Transfer in Pulsating Atmospheres: Cepheids.- New Opacities and First Overtone Mode Cepheids.- Coupled Oscillators.- An Oscillator Model for Stellar Variability.- The Coupling Coefficients of Pulsation for Radiative Stellar Models.- The Coupling Coefficients of Radial Pulsation in Third Order.- The Role of Convection in Reducing Nonadiabaticity and Mode Coupling in Cepheids.- The Effect of Convection in Nonlinear One-Zone Stellar Models.- A Unified Model of Dwarf Nova Outbursts Based on the Disk Instability.- Pulsational Instability of Accretion Disks around Compact Objects.- Numerical Simulations of Pulsationally Unstable Accretion Disks around Supermassive Black Holes.- Long-Term V/R Variations of Be Stars Due to Global One-Armed Oscillations of Equatorial Disks.- A Simplified Model for a Nonlinear Tidal Effect on Accretion Disks in CVs.- List of Participants.