1995A&A...295L..39C

We report the detection of the millimeter recombination lines H40α, H30α, H29α, H50β and H37β towards η Carinae (η Car). All the recombination lines show a similar line profile. A strong narrow component is seen at a velocity of V_lsr~-50km/s, significantly blue-shifted with respect to the systemic velocity of η Car (-16km/s). Underlying this main component a very broad emission is also detected in the α lines, extending from ~-200 to ∼100km/s. The profiles are markedly asymmetrical in the sense of enhanced blue-shifted emission both in the narrow and the broad features. We argue that most of the red-shifted emission is absorbed by the optically thick, strong radio continuum of the ionized stellar wind of η Car and that the millimeter recombination lines are affected by maser emission. This is supported by simple model calculations for the radiation transfer of the line and continuum emission in η Car.