Solar and Stellar Granulation

Robert J. Rutten Sterrekundig Instituut Utrecht, The Netherlands Why this workshop? Why this workshop? Or rather, since the real question that arose about a year ago was not whether there should be another OAC workshop, but only what it should be about: why a workshop on granulation? To answer this question I will play an unfair trick on you. I will simply present the scientific justification which I included last autumn in a grant application to NATO's Scientific Affairs Division. It lists the reasons why I thought a workshop on this particular topic and at this particular moment ought to be worthwhile. There must be something in its reasoning, because NATO has indeed agreed to co-sponsor this workshop, and because all of you have decided to spend time and effort on your contributions and to journey to this beautiful island in order to participate. But since the proof is in the pudding, I am eager to see whether indeed this workshop will be as outstanding as I have promised; in the meantime, you are entitled to know what we got you here for. The justification went as follows: "The subject 'granulation' has recently become a hot topic, at the center of much new research, observational as well as interpretational and theoretical, and both in solar physics and in stellar physics.

Contenu

Workshop Introduction.- 1: Observational Techniques.- Observations of the Solar Granulation at the Pic Du Midi Observatory and with THEMIS.- The Gregory-Coudé-Telescope at the Observatorio Del Teide, Tenerife.- The Status of the Latest German Solar Facility on Tenerife.- Ground-Based Tunable Filter Observations.- An Overview of the Orbiting Solar Laboratory.- Solar Image Restoration by Adaptive Optics.- Improving Solar Image Quality by Image Selection.- Reconstruction from Focal Volume Information.- Granulation in the Photospheres of Stars.- Solar Granulation Speckle Interferometry Using Cross-Spectrum Techniques.- Active Optics, Anisoplanatism, and the Correction of Astronomical Images.- On Pressure Shifts of Fel Lines in Stellar Atmospheres.- Pressure Broadening and Solar Spectral Line Bisectors.- 2: Observations.- Solar Granulation: Overview.- Line Shifts in the Infrared Spectra of Late-Type Stars.- Asymmetry of Absorption Lines in the Solar and Procyon Spectra.- Line Asymmetries in Late-Type Dwarf Photospheres.- Challenges and Opportunities in Stellar Granulation Observations.- High Resolution Granulation Observations from La Palma: Techniques and First Results.- Spatially Resolved Spectra of Solar Granules.- Granulation Line Asymmetries.- Granulation and Waves?.- High Resolution Diagnostic of the Mesocells in the Solar Temperature Minimum Region.- Pole-Equator Difference of the Size of the Chromospheric Ca II-K Network in Quiet and Active Solar Regions.- Temperature Waves and Solar Granulation.- Flows, Random Motions and Oscillations in Solar Granulation Derived 225 the SOUP Instrument on Spacelab 2.- Granulation In and Out of Magnetic Regions.- Observation and Interpretation of Photospheric Line Asymmetry Changes near Active Regions.- Line Bisectors In and Out Magnetic Regions.- RMS Velocities in Solar Active Regions.- Report on the Session: Position and Discussion - Solar Data.- The Limb Effect of the KI 769.9 nm Line in Quiet Regions.- Vortex Motion of the Solar Granulation.- The Granulation Sensitivity of Neutral Metal Lines.- Granule Lifetimes and Dimensions as Function of Distance from a Solar Pore Region.- Spatio-Temporal Analysis of Waves in the Solar Atmosphere.- On the Granule Lifetime Near and Far Away from Sunspots.- Observations of High Frequency Waves in the Solar Atmosphere.- Photoelectric Analysis of the Solar Granulation in the Infrared.- Constraints Imposed by Very High Resolution Spectra and Images on Theoretical Simulations of Granular Convection.- The Variation of the Mean Size of the Photospheric Granules Near and Far from a Sunspot.- Abnormal Granulation.- Supergranular Pattern Formed by the Large Granules.- Details of Large Scale Solar Motions Revealed by Granulation Test Particles.- 3: Modelling.- Convection and Waves.- How Much Can Theoretical Models of Compressible Convection Tell Us about Solar Granulation?.- Two and Three-Dimensional Simulations of Compressible Convection.- Spectroscopic Properties of Solar Granulation obtained from 2-D Numerical Simulations.- On the Influence of Opacity Fluctuations on the Energy Transfer by Radiation.- Simulating Magnetoconvection.- Time Dependent Compressible Magnetoconvection.- Models of Magnetic Flux Sheets.- Stellar Granulation: Modeling of Stellar Surfaces and Photospheric Line Asymmetries.- Three-Dimensional Simulation of Convective Motions in the Procyon Envelope.- Numerical Simulations of Gas Flows in an A-Type Stellar Atmosphere.- Inhomogeneous Chromospheric Structures in the Atmosphere of Arcturus Generated by Acoustic Wave Propagation.- Interaction of Solar Granulation with Weak and Strong Magnetic Fields.- Granulation and the NLTE Formation of K I 769.9.- The Effects of Inhomogeneities in 3-D Models on Abundance Determinations.- 2-D Flux Tube in Radiative Equilibrium.- Isolated Magnetohydrodynamic Thermal Eddies in a Thermally Stratified Fluid.- What Do the Mg II Lines Tell Us About Waves and Magnetic Fields?.- A Simple Model of Mesogranular and Supergranular Flows.- Probing of Sunspot Umbral Structure by Oscillations.- Workshop Impressions.- Granulation Bibliography (compiled by K.L. Harvey).