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C. Sanchez Contreras, R. Sahai (JPL)
We analyse (archival) optical long-slit spectra of the Protoplanetary Nebula He3-1475 taken with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (GO7285, PI: P. Harrington). This object shows a remarkable bipolar morphology and clear evidence of shocks probably resulting from the interaction between a fast, collimated wind and the slowly expanding envelope formed during the Asymptotic Giant Branch evolution of the central star. This shock interaction is the mechanism thought to be responsible for the shaping of planetary nebulae.
A total of eight 0\farcs1-wide slits parallel to the main symmetry axis of the nebula were used, providing, with unprecedented detail, its structure and kinematics, specially of its innermost regions. The presence of two blue-shifted absorption features in the H\alpha profile, suggest two different components of gas outflowing at high velocity (~1000 and ~\,300\,km\,s-1). The ultrahigh- and high-velocity absorption features are present in the NW lobe (closer to us) at all locations from the stellar position up to offsets of ~\,0\farcs3 and ~\,0\farcs6, respectively. In addition, the larger the distance from the star, the deeper and larger the velocity shift of the 300\,km\,s-1 feature. These gradients could suggest that the outflowing gas between the observer and the continuum source (probably background dust), leading to this high-velocity feature, is probably collimated rather than isotropic at a distance of ~\,5\times1015\,cm (for an isotropic wind the deepest and bluest-shifted absortion is expected at the nebula center). We note, however, that other explanations may be possible. Extended emission in H\alpha, [OI]\lambda\lambda6300,63, [NII]\lambda\lambda6548,83, and [SII]\lambda\lambda6316,31 is also detected from several outer (>2\arcsec) shock-excited knots in the nebula. In order to correctly interpret the complex He3-1475 spectra (that also include line and continuum scattered light) we intend to analyse the data through modelling of the spectral profiles considerig different geometries, kinematics and physical conditions in the gas.
This work is partially funded through a NASA LTSA grant to R.S.