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Astron. Astrophys. 345, L39-L42 (1999)

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Letter to the Editor

IRAS 04296+3429: a 21 µm source with a very strong 30 µm emission band *

R. Szczerba 1,2, Th. Henning 3, K. Volk 2, S. Kwok 2 and P. Cox 4

1 N. Copernicus Astronomical Center, Rabiaska 8, PL-87-100 Toru, Poland (szczerba@ncac.torun.pl)
2 Department of Physics and Astronomy, University of Calgary, Calgary, Canada (Volk, Kwok@iras.ucalgary.ca)
3 Astrophysikalisches Institut und Universitäts-Sternwarte, Jena, Germany, (henning@astro.uni-jena.de)
4 Institut d'Astrophysique Spatiale, Université de Paris XI, Orsay, France (cox@ias.fr)

Received 15 January 1999 / Accepted 17 April 1999


We report the detection of the 30 µm emission feature from the C-rich post-Asymptotic Giant Branch (post-AGB) star IRAS 04296+3429 based on ISO SWS observations. ISO data show that there is a clear substructure in the 30 µm feature in the form of a plateau which extends from 26 to 27 µm. This is confirmed by the ISO SWS data for another post-AGB object IRAS 22272+5435, which has the strongest known 30 µm band accounting for about 24% of its total infrared (IR) emission or 12% of the bolometric luminosity. In the case of IRAS 04296+3429 we estimate that about 85% of the total energy is emitted in the infrared of which about 15-22% (depending on the estimated continuum level) is contributed by the 30 µm band. The total energy emitted in the band is at least comparable for both sources, while the energy emitted in the 21 µm band seems to be about 3 times larger in the case of IRAS 04296+3429, if they have the same bolometric luminosity. Grains of pure MgS could be responsible for the observed 30 µm feature provided they have a broad distribution of shapes, but they cannot account for the observed plateau emission. Small graphite grains with relatively thick MgS coating could be responsible for the observed substructure, but we were not able to definitively solve the question of their contribution to the 30 µm band.

Key words: stars: AGB and post-AGB – stars: circumstellar matter – stars: individual: IRAS 04296+3429 – stars: individual: IRAS 22272+5435 – radiative transfer

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with participation of ISAS and NASA

Send offprint requests to: Ryszard Szczerba (szczerba@ncac.torun.pl)

© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999