IUE and ISO observations of the bipolar proto-planetary nebula Hen 401 (IRAS 10178-5958)*
National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
2 Indian Institute of Astrophysics, Bangalore-560034, India
3 ISO Data Centre, Astrophysics Division, Space Science Department of ESA, VILSPA, 28080 Madrid, Spain
4 Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Naples, Italy
5 Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
6 Kiso Observatory, School of Science, University of Tokyo, Mitake, Kiso, Nagano 397-0101, Japan
7 Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
8 Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, Apartado de Correos 50727, 28080 Madrid, Spain
Corresponding author: M. Parthasarathy, firstname.lastname@example.org
Accepted: 29 June 2001
We present ultraviolet (IUE) and infrared (ISO) observations of the bipolar proto-planetary nebula Hen 401 which, combined with previously available optical and near infrared data, are used to reconstruct the overall spectral energy distribution from 1150 Å to 100 μm. The ISO spectrum is dominated by strong PAH emission superimposed on a very cold continuum which is interpreted as thermal emission originating in the C-rich cool dust (~106 K) present in the circumstellar envelope, the remnant of the previous AGB phase. In addition, a second, hotter component detected in the near infrared is attributed to thermal emission from hot dust (~640 K), suggesting that mass loss and dust grain formation is still on-going during the current post-AGB phase. The ultraviolet (IUE) spectrum shows a stellar continuum in the wavelength interval 2400 Å to 3200 Å which corresponds to a moderately reddened B8-type central star. Unexpectedly, the UV flux in the wavelength interval 1150 Å to 1900 Å is very weak or absent with no evidence of a hotter binary companion which could explain the detection of the nebular emission lines observed in the available ground-based optical spectra of Hen 401. HST WFPC2 high resolution images also show no indication of a hot companion to the B8-type central star observed both in the optical and in the UV. The evolutionary implications of a possible single nature for the central star of Hen 401 are discussed.
Key words: planetary nebulae: individual: Hen 401 / ultraviolet: stars / stars: evolution / stars: emission-line, Be / stars: AGB and post-AGB
Based on observations obtained with the International Ultraviolet Explorer, retrieved from the INES Archive at VILSPA, Madrid, Spain, and observations made with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the UK) with the participation of ISAS and NASA.
© ESO, 2001