Constraining the wind launching region in Herbig Ae stars:: AMBER/VLTI spectroscopy of HD 104237

Aims. We investigate the origin of the Br gamma emission of the Herbig Ae star HD 104237 on Astronomical Unit (AU) scales. Methods. Using AMBER/VLTI at a spectral resolution R = 1500 we spatially resolve the emission in both the Br gamma line and the adjacent continuum. Results. The visibility does not vary between the continuum and the Br gamma line, even though the line is strongly detected in the spectrum, with a peak intensity 35% above the continuum. This demonstrates that the line and continuum emission have similar size scales. We assume that the K-band continuum excess originates in a puffed-up inner rim of the circumstellar disk, and discuss the likely origin of Br gamma. Conclusions. We conclude that this emission most likely arises from a compact disk wind, launched from a region 0.2 - 0.5 AU from the star, with a spatial extent similar to that of the near infrared continuum emission region, i.e., very close to the inner rim location.