In stably stratified stars, numerical magneto-hydrodynamics simulations have shown that arbitrary initial magnetic fields evolve into stable equilibrium configurations, usually containing nearly axisymmetric, linked poloidal and toroidal fields that stabilize each other. In this work, we test the hypothesis that stable stratification is a requirement for the existence of such stable equilibria. For this purpose, we follow numerically the evolution of magnetic fields in barotropic (and thus neutrally stable) stars, starting from two different types of initial conditions, namely random disordered magnetic fields, as well as linked poloidal-toroidal configurations resembling the previously found equilibria. With many trials, we always find a decay of the magnetic field over a few Alfvén times, never a stable equilibrium. This strongly suggests that there are no stable equilibria in barotropic stars, thus clearly invalidating the assumption of barotropic equations of state often imposed on the search of magnetic equilibria. It also supports the hypothesis that, as dissipative processes erode the stable stratification, they might destabilize previously stable magnetic field configurations, leading to their decay.On the other hand, attempting to construct plausible axisymmetric magnetic equilibria for these stars, several authors (Tomimura & Eriguchi 2005; Yoshida et al.

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Background: Detailed experimental knowledge of the level structure of light weakly bound nuclei is necessary to guide the development of new theoretical approaches that combine nuclear structure with reaction dynamics.Purpose: The resonant structure of 8 B is studied in this work.Method: Excitation functions for elastic and inelastic 7 Be+p scattering were measured using a 7 Be rare isotope beam. Excitation energies ranging between 1.6 and 3.4 MeV were investigated.An R-matrix analysis of the excitation functions was performed. Conclusions: Identification of the 0 + , 2 + , 1 + states that were predicted by some models at relatively low energy but never observed experimentally is an important step toward understanding the structure of 8 B. Their identification was aided by having both elastic and inelastic scattering data. Direct comparison of the cross sections and phase shifts predicted by the TDCSM and ab initio No Core Shell Model coupled with the resonating group method is of particular interest and provides a good test for these theoretical approaches.

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Excitation functions of elastic and inelastic 7 Be + p scattering were measured in the energy range between 1.6 and 2.8 MeV in the c.m. An R-matrix analysis of the excitation functions provides strong evidence for new positive parity states in 8 B. A new 2 + state at an excitation energy of 2.55 MeV was observed, and a new 0 + state at 1.9 MeV is tentatively suggested. The R-matrix and time-dependent continuum shell model were used in the analysis of the excitation functions. The new results are compared to the calculations of contemporary theoretical models.

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