Abstract. High-resolution spectra of 13 core helium-burning stars in the thick disk of the Galaxy have been obtained with the SOFIN spectrograph on the Nordic Optical Telescope to investigate abundances of up to 22 chemical elements. Abundances of carbon were studied using the C2 Swan (0, 1) band head at 5635.5Å. The wavelength interval 7980-8130Å with strong CN features was analysed in order to determine nitrogen abundances and 12 C/ 13 C isotope ratios. The oxygen abundances were determined from the [O i] line at 6300Å. Abundances in the investigated stars suggest that carbon is depleted by about 0.3 dex, nitrogen is enhanced by more than 0.4 dex and oxygen is unaltered. The 12 C/ 13 C ratios are lowered and lie between values 3 and 7 which is in agreement with "cool bottom processing" predictions (Boothroyd & Sackmann 1999). The C/N ratios in the investigated stars are lowered to values between 0.7 and 1.2 which is less than present day theoretical predictions and call for further studies of stellar mixing processes. Abundance ratios of O, Mg, Eu and other heavy chemical elements to iron in the investigated stars show a pattern characteristic of thick disk stars. The results provide evidence that the thick disk population has a distinct chemical history from the thin disk. The onset of the bulk of SN Ia is suggested to appear at [Fe/H] ≈ −0.6 dex.

We use three-dimensional simulations to study compressible convection in a rotating frame with magnetic fields and overshoot into surrounding stable layers. The, initially weak, magnetic field is amplified and maintained by dynamo action and becomes organized into flux tubes that are wrapped around vortex tubes. We also observe vortex buoyancy which causes upward flows in the cores of extended downdraughts. An analysis of the angles between various vector fields shows that there is a tendency for the magnetic field to be parallel or antiparallel to the vorticity vector, especially when the magnetic field is strong. The magnetic energy spectrum has a short inertial range with a slope compatible with k+lI3 during the early growth phase of the dynamo. During the saturated state the slope is compatible with k-'. A simple analysis based on various characteristic timescales and energy transfer rates highlights important qualitative ideas regarding the energy budget of hydromagnetic dynamos.

The dynamic state of the interstellar medium, heated and stirred by supernovae (SNe), is simulated using a three-dimensional, nonideal MHD model in a domain extended kpc horizontally and 2 kpc vertically, 0.5 # 0.5 with the gravitational field symmetric about the midplane of the domain, . We include both Type I and z ϭ 0 Type II SNe, allowing the latter to cluster in regions with enhanced gas density. The system segregates into two main phases: a warm, denser phase and a hot, dilute gas in global pressure equilibrium; there is also dense, cool gas compressed into filaments, shells, and clumps by expanding SN remnants. The filling factor of the hot phase grows with height, so it dominates at kpc. The multicomponent structure persists throughout the FzF տ 0.5 simulation, and its statistical parameters show little time variation. The warm gas is in hydrostatic equilibrium, which is supported by thermal and turbulent pressures. The multiphase gas is in a state of developed turbulence. The rms random velocity is different in the warm and hot phases, 10 and 40 km s Ϫ1 , respectively, at FzF Շ 1 kpc; the turbulent cell size (twice the velocity correlation scale) is about 60 pc in the warm phase.

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