We have presented the detection of several HI recombination lines from the Brackett, Pfund and Humphreys series towards the two Herbig Ae/Be stars CoD 11721 and MWC1080, obtained with the Short Wavelength Spectrometer on-board ISO. These lines have been analyzed adopting an ionized wind model; the conclusions from this analysis are the following:
- all the observed line ratios are higher than expected from optically thin recombination, but they are also higher than those predicted by common wind models which assume a density bounded ionized region. This discrepancy is more evident for the higher lines of each series;
- the observed line decrements can instead be explained by assuming that the star does not have enough UV photons to ionize the envelope entirely and that the photons are all absorbed in the inner, high optically thick part of the wind. The data are well fit by ionized regions extending only a few stellar radii;
- with the above assumption, from both the line ratios and the absolute intensities, we consistently derive the mass loss rate, the dimension of the ionized region and the distance to the two stars.
© European Southern Observatory (ESO) 1998
Online publication: September 30, 1998