Evolution of the internal structure, the angular momentum accretion rate, and the equatorial surface velocity of the test-model at low mass-accretion rate described in Sect. 3.1, as a function of the increasing stellar mass, which is a time-coordinate in the case of accretion. Upper panel: radius (blue curve) and the internal structure, with convective zones in dark grey and radiative zones in light grey. The dark grey dotted curves are iso-mass of M_r = 1, 2, 3,..., M_⊙. Second panel: angular momentum accretion rate in logarithm of . Third panel: surface velocity (at the equator) and the fourth panel shows the ratio of the surface velocity to the critical velocity. (The critical limit is indicated by the horizontal grey dotted line.)