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Context. AGB stars have long been held responsible for the important star-to-star variations in light elements observed in Galactic globular clusters (GCs).

Aims. We discuss the properties of the progenitors of core collapse supernovae of type Ib and Ic and of long soft gamma ray bursts, as they can be deduced from rotating stellar models of single stars at various metallicities.

Aims.We study the effects of rotation on the outer convective zones of massive stars.Methods.We examine the effects of rotation on the thermal gradient and on the Solberg-Hoiland term by analytical developments and by numerical models.Results.Writing the criterion for convection in rotating envelopes, we show that the effects of rotation on the thermal gradient are much larger and of opposite sign to the effect of the Solberg-Hoiland criterion. On the whole, rotation favors convection in stellar envelopes at the equator and to a smaller extent at the poles. In a rotating 20?M?star at 94% of the critical angular velocity, there are two convective envelopes, with the bigger one having a thickness of 13.2% of the equatorial radius. In the non-rotating model, the corresponding convective zone has a thickness of only 4.6% of the radius. The occurrence of outer convection in massive stars has many consequences.

The hot Neptune orbiting around GJ?436 is a unique example of an intermediate mass planet. Its close-in orbit suggests that the planet has undergone migration and its study is fundamental to understand planet formation and evolution. As it transits its parent star, it is the only Neptune-mass extrasolar planet of known mass and radius, being slightly larger and more massive than Neptune (M=22.6?M, R=4.19?R). In this regime, several bulk compositions are possible: from an Earth-like core with a thick hydrogen envelope to a water-rich planet with a thin hydrogen envelope, and comprising a Neptune-like structure. We combine planet-structure modelling with an advanced planet-formation model to assess the likelihood of the different possible bulk compositions of GJ?436?b. We find that both an envelope-free water planet (?Ocean planet?) as well as a diminute version of a gaseous giant planet are excluded. Consisting of a rocky core with a thick hydrogen/helium envelope, a ?dry? composition produces not only too small a radius but is also a very unlikely outcome of planet formation around such a low-mass star. We conclude that GJ?436?b is probably of much higher rock content than Neptune (more than 45% in mass), with a small H-He envelope (10-20% in mass). This is the expected outcome of the gathering of materials during the migration process in the inner disk, creating a population of which the hot Neptune is representative. ?

Context.Whenever stars rotate very rapidly, such that Ω/Ωcrit> 0.7 where Ωcritis the Keplerian angular velocity of the star accounting for its deformation, radiative stellar winds are enhanced in polar regions. This theoretical prediction has now been confirmed by interferometric observations of rapidly rotating stars.

Context.Since the external regions of the envelopes of rapidly rotating early-type stars are unstable to convection, a coupling may exist between the convection and the internal rotation.

Context.Light elements and nitrogen surface abundances together can constrain the mixing efficiencies in massive stars on the main sequence, because moderate mixing in the surface layers leads to depletion of light elements but only later to enrichment in nitrogen.

Context. The three most iron-poor stars presently known ([Fe/H] equal to –5.96, –5.4 and –4.75) are carbon-rich, so they are called C-Rich Ultra-Metal Poor Stars (CRUMPS). The origin of their peculiar surface abundances is not understood.