Optical and infrared observations of the bipolar proto-planetary nebula Henize 401

Based on optical and near-infrared ground-based spectroscopy and optical an d near-infrared Hubble Space Telescope (HST) images, we confirm the classif ication of Hen 401 as a bipolar proto-planetary nebula. HST images reveal a highly elongated morphology, consisting of two main bipolar lobes of unequ al surface brightness separated by a dark lane of dust with a total extensi on of 28" x 3", superimposed on a much fainter background emission of ellip tical shape extending over similar to 10" x 5". The simultaneous detection of spectral lines formed under very different density conditions, together with the strong obscuration observed along the equatorial plane, is interpr eted as the signature of a circumstellar disk, which would be responsible f or the strong collimation observed. We conclude that the emission observed is mainly due to scattering of the light originated in the fluorescence-exc ited inner region of the circumstellar disk. In addition, we also report th e detection of strong molecular H-2 emission in the near infrared, confirmi ng that the onset of the H-2 emission occurs in proto-PNs after the bipolar structure has developed, but before photoionization takes place.