Spherical-shell boundaries for two-dimensional compressible convection in a star J. Pratt, I. Baraffe, T. Goffrey, C. Geroux, M. Viallet, D. Folini, T. Constantino, M. Popov and R. Walder A&A, 593 (2016) A121 Published online: 04 October 2016 DOI: 10.1051/0004-6361/201628296