Helioseismology has provided robust estimates of global properties of the solar convection zone, its depth, stratification, and revealed rotational shear layers at the boundaries. New methods of local helioseismology provide 3D maps of subsurface convective flows. In the quiet Sun regions, these maps reveal that supergranular-scale convection extends to the depth of 12–15 Mm. Analysis of evolution of the supergranular convection pattern shows evidence for a wave-like behavior which might be related to the interaction between convection and the subsurface rotational sheer layer. Helioseismology also reveals large-scale circulation flows around magnetic regions. These flows affect the evolution of the mean meridional flow during the solar cycle and, probably, the magnetic flux transport from mid-latitudes to the polar regions, a process important for solar dynamo theories. Helioseismic measurements on a smaller scale, below sunspots, give insight on how convection interacts with strong magnetic fields.

In the Sun, the convection zone reaches up to the solar photosphere and can thus directly influence the emergent spectrum. Traditionally, the effects of convection has been modelled with the local mixing length theory in theoretical 1D hydrostatic model atmospheres. In a different approach, we have performed realistic time-dependent, 3D, radiative-hydrodynamical simulations of the outer layers of the solar convection zone, including the photosphere. Both the different mean stratification and the presence of atmospheric inhomogeneities in 3D impact the spectral line formation. In a series of papers, we have applied our 3D solar model atmosphere to the problem of the solar chemical composition. Furthermore, we have adopted the best possible atomic and molecular line data and taken into account departures from LTE in the line formation when necessary. The inferred C, N, O and Ne abundances are all significantly lower than estimated from previous 1D modelling by 0.2-0.3 dex. These results have significant implications for a range of topics in contemporary astrophysics, including causing a severe headache for helioseismology.

Asteroseismology—using stellar oscillations to study the interiors of stars—is a relatively new and growing research field in astrophysics. Oscillations are found in stars of most masses and essentially all stages of evolution. Their frequencies are determined by the internal sound speed and density structure of the star, as well as rotation, convection processes and possibly effects of magnetic fields. Recent developments have led to a breakthrough in our ability to study the details of cores of solar-like stars and it is foreseen that a number of key science questions will be addressed through the analysis of frequencies and other properties of stellar oscillations. In this paper we review some of the latest results from asteroseismology of solar-like stars, with the focus on properties of convection.

We present a detailed comparison between high resolution observations of a quiet solar region and simulated spectra in several 3-D snapshots of a realistic radiation-hydrodynamical simulation of the solar atmosphere. We find excellent agreement between the two data sets, thus providing strong support to the realism of the simulations, and confirming the high quality of the instrumentation. We propose that spatially resolved spectral data can be employed as a complementary tool to more classic analysis for investigating the hotly debated topic of solar abundances.

A summary of the round table discussion following Session B on Observational Probes of Convection.

Convection and turbulence in stellar atmospheres have a significant effect on the emergent flux from late-type stars. The theoretical advancements in convection modelling over recent years have proved challenging for the observers to obtain measurements with sufficient precision and accuracy to allow discrimination between the various predictions. An overview of the current observational techniques used to evaluate various convection theories is presented, including photometry, spectrophotometry, and spectroscopy. The results from these techniques are discussed, along with their successes and limitations. The prospects for improved observations of stellar fluxes are also given.

We present and discuss the results of a comprehensive analysis of magnetic field measurements for a group of seven young Herbig Ae/Be stars obtained using low-resolution spectropolarimetry with FORS1 at the VLT. The first definite evidence for the presence of surface magnetic fields has been found only recently in the Herbig Ae stars HD 139614, HD 31648 and HD 144432 (Hubrig et al. 2004; Hubrig et al. 2006) from the measurement of circular polarization in Ca II lines and hydrogen lines located in the spectral region from 3900 to 4900 Å. The unusual Herbig Ae star HD 190073 shows distinctive Zeeman features in the Ca II doublet which displays several components in both H and K lines. The most recent analysis carried out separately for different lines has shown that Zeeman features appear in metallic lines in all seven objects of our programme. The most prominent of them are seen in lines of the CaII doublet possibly of both photospheric and circumstellar origin. The circumstellar Balmer line components demonstrate the existence of a magnetic field in HD 144432 and HD 31648. The photospheric components of these lines with signs of magnetic field are present in HD 144668.

I found evidence that the X-ray surface flux of intermediate-mass G and K giants is correlated with their rotation period and Rossby number. Confidence in the degree of correlation is significantly higher when stellar gravity is taken into account. An empirical relation is found that accounts for the X-ray luminosity evolution of single intermediate-mass giants and giants in close or long-period binary systems, such as RS CVn-type systems, as they evolve off the main sequence towards the top of red giant branch.

The fundamental properties of detached eclipsing binary stars can be measured very accurately, which could make them important objects for constraining the treatment of convection in theoretical stellar models. However, only four or five pieces of information can be found for the average system, which is not enough. We discuss studies of more interesting and useful objects: eclipsing binaries in clusters and eclipsing binaries with pulsating components.

The current status of microturbulent velocity and abundance determinations for A and F dwarfs in open clusters is reviewed. A programme to observe several tens of A and F dwarfs in open clusters of various ages was initiated several years ago. We have performed high resolution high signal-to-noise spectroscopy of stars well distributed in mass along the Main Sequence. Microturbulent velocities and abundances of several chemical elements have been derived iteratively by fitting grids of synthetic spectra calculated in LTE to the observed spectra. Curve of growths were used in a few instances as well. The results obtained are reviewed for Coma Berenices, the Pleiades, Alpha Persei and the Ursa Major moving group.

The microturbulent velocities exhibit a broad maximum in the range A5V to about F0V as indicated in Smalley (2004).

Reversed granulation is predicted by numerical simulations and has been observed in the wings of chromospheric lines. Here we present reversed granulation in high spatial, spectral and temporal resolution, extracted from the photospheric Fe I 7090.4 Å line core intensities, once taking into account the velocity effects. Correlations with the continuum are studied in terms of smoothing, time delay and temporal evolution. The latter appears to be superimposed with an oscillatory signal that suggests the presence of gravity waves in the mid-photosphere.

Microturbulence is usually treated in model atmospheres as a free parameter (ξt) that allows to re-establish agreement among abundances derived from different lines. Even if this parameter is a consequence of treating a 3D problem as a 1D one, it seems clear that microturbulence is linked to the velocity field within the atmosphere, and therefore to convection in the external layers. The values of the parameter as determined from observations show a dependence both on effective temperature and on surface gravity. In this paper we study how the microturbulence parameter used in the atmosphere models affects the theoretical color-magnitude diagram (CMD). First, in the Main Sequence (MS) domain due to the dependence of the microturbulence parameter on Teff; and second, in the giant branch (Pre-main sequence and Red Giant Branch) where several photometric indexes show a large variation due to the increase of the microturbulence parameter as the stellar gravity decreases. We predict then a significant change in the CMD, as well as in the color-temperature calibrations, if variations of ξt such as those observationally determined are included in theoretical CMD computations.

Narrow band photometry is a useful tool to characterize large numbers of stars, but observed colors and indices must be connected to astrophysical parameters by synthetic photometry. We present synthetic Hβ indices calculated from 1D model atmospheres implementing different convection treatments. The calculated indices are transformed to the standard system using observed medium-resolution spectra. We test the synthetic photometry with observed indices of eclipsing binary systems. The computed indices agree with the observed ones up to an amount expected from the observational errors, the accuracy of the atmospheric parameters, and computational uncertainties.

The site testing program for the Thirty-Meter-Telescope (TMT) is monitoring the seeing conditions above several mountains. Observations are presented which show that the ground layer seeing (0 m–500 m above the ground) is influenced by the onset of free convection. It is shown that under radiation dominated conditions, indicating free convection of the atmosphere above the site, the occurence of the very best seeing conditions is supressed. A quantitative threshold for these conditions is given, allowing to estimate the shortterm future stability of the ground layer seeing.

Three basic modeling approaches have been used to numerically simulate fluid turbulence and the banded zonal winds in the interiors and atmospheres of giant planets: shallow-water models, deep-shell Boussinesq models and deep-shell anelastic models. We review these models and discuss the approximations and assumptions upon which they are based. All three can produce banded zonal wind patterns at the surface. However, shallow-water models produce a retrograde (i.e., westward) zonal jet in the equatorial region, whereas strong prograde (i.e., eastward) equatorial jets exist on Jupiter and Saturn. Deep-shell Boussinesq models maintain prograde equatorial jets by the classic method of vortex stretching of convective columnar flows; however, they neglect the effects of the large density stratification in these giant planets. Deep-shell anelastic models account for density stratification and maintain prograde equatorial jets by generating vorticity as rising fluid expands and sinking fluid contracts, without the constraint of long thin convective columns.

Numerical simulations of convection-driven dynamos in rotating spherical shells are employed to better understand the observed strength and geometry of planetary magnetic fields. The model computations cannot be performed for realistic values of several of the control parameters. By varying parameters within the accessible range, it is possible to derive scaling laws for the magnetic field strength and the flow velocity in the dynamo region and for the dipole moment. Our scaling laws suggest that, even though diffusivities are far too large in the models, diffusive processes do not play an important role, just as in planetary cores. Extrapolating the scaling laws to planetary values of the control parameters leads to reasonable predictions for the field strength in the dynamo region and fits the observed dipole moments decently, in particular in the cases of Earth and Jupiter. For Mercury, which does not fit well when applying the scaling laws in a straightforward way, a model is proposed in which the upper part of the fluid core is stably stratified and the dynamo operates only in its deep regions. The time-varying dynamo field must diffuse through the stable region and is attenuated by the skin effect. The model explains why Mercury has a very weak but probably dipole-dominated magnetic field.

The giant planets are fluid objects; their solid cores occupy much less than half of their volumes. The largest planet, Jupiter, is over ten times the size of Earth. The giant planet atmospheres are powered in roughly equal parts by sunlight and by internal heat, which is left over from planetary formation. In most cases, the winds are measured by tracking clouds relative to the internal magnetic fields. Saturn is the exception, since the internal field is axisymmetric and therefore provides no evidence of rotation. In all four giant planets, the winds blow mainly in the east-west (zonal) direction, and the coloured cloud bands are aligned with the winds. The patterns are organized by rotation and not by the energy sources, since the sun at zenith moves from one pole to the other during the course of a year on Uranus, and yet the winds do not change. Although the power per unit area - the sum of absorbed sunlight and internal heat - is 20 times greater at Jupiter than at Neptune, the winds at Neptune are stronger. In fact Jupiter has the weakest winds of all the giant planets, although it is closest to the sun. Besides the zonal winds, the giant planets have long-lived vortices that have the same sign of vorticity as the latitude bands in which they sit. These large vortices exhibit a variety of behaviours, including oscillation in shape, position, and orientation, merging and splitting, and filament ejection. The anticyclones have a compact, oval shape; the cyclones are more elongated and diffuse. The cyclones contain lightning, which is a sign of moist convection. The cyclones therefore have a more disturbed appearance, since the convective storms are vigorous and chaotic. The convective storms are more frequent on Jupiter, but they are apparently more energetic on Saturn. The convective storms maintain a Reynolds stress that pumps momentum into the zonal jets in what is known as an inverse energy cascade. The depth to which the zonal winds extend is largely unknown. The winds could be confined to the outer 1 percent of the planets radii, or they could extend down into the fluid interiors, where the electrical conductivity and magnetic field become important.

We briefly review the crucial effect that convection plays in the evolution, interior and atmospheric physics of brown dwarfs. In particular, we discuss: (1) the role of convection in the interior structure and evolution of brown dwarfs (BDs); (2) the importance of convection in the atmospheres of ultra-cool objects, at both high and low gravities (i.e., in both young and old BDs); and (3) the role of convection/turbulence in the formation and settling of dust grains, and non-equilibrium chemistry, in BD atmospheres.

We discuss prospects of using multi-dimensional time-dependent simulations to study the atmospheres of brown dwarfs and extrasolar giant planets, including the processes of convection, radiation, dust formation, and rotation. We argue that reasonably realistic simulations are feasible, however, separated into two classes of local and global models. Numerical challenges are related to potentially large dynamic ranges, and the treatment of scattering of radiation in multi-D geometries.

Convection theories for star and planet formation studies have to be (1) simple, to allow a self-consistent solution with other relevant processes, (2) time-dependent, because convection often starts in collapse-flows, and (3) robust, i.e. physically well-behaved under a wide range of conditions ranging from the quiet protoplanetary nebula to supercritical protostellar accretion-shocks with Mach-numbers of a few hundred. I describe how the equations of radiation fluid-dynamics can be augmented by a one-equation convection model in order to construct a system of equations that contains the Sun, brown dwarfs and planets as well as their nearly isothermal parent-clouds. The system of equations is calibrated to the Sun and tested by the solar convection zone and the pulsations of RR-Lyrae stars. I discuss the following applications: (1) star formation as the collapse of Bonnor-Ebert spheres of masses ranging from the stellar domain to the brown dwarf region, (2) the approach to the main sequence, (3) companion mass determinations for direct imaging searches for exoplanets, with GQ Lupi as an example, and (4) the formation of Pegasi-planets, and the “large core” exoplanet, HD 149 026, in particular.