Astron. Astrophys. 315, L333-L336 (1996)
The 6.0 and 6.8 m absorption features in the spectrum of NGC 7538: IRS9*
W.A. Schutte1, A.G.G.M. Tielens2, D.C.B. Whittet3, A. Boogert4, P. Ehrenfreund1, Th. de Graauw4, T. Prusti5, E.F. van Dishoeck1, and P. Wesselius4,
1 Leiden Observatory, P. O. Box 9513, 2300 RA Leiden, The
Received 15 July 1996 / Accepted 22 August 1996
Abstract. Short Wavelength Spectrometer observations of the 6.0 and 6.8 m absorption features towards the obscured young stellar object NGC 7538: IRS9 are presented and compared to the features of a number of species measured in the solid phase. It is found that while solid provides the bulk of the 6 m band, additional absorption is required near 5.83 m and 6.25 m. It is proposed that formic acid (HCOOH) is a plausible candidate for the blue excess, while the red excess could be related to the C-C stretching mode in aromatic structures. Subsequently, a number of candidates for the 6.8 m band are reviewed. Unfortunately, none of these appears to satisfy the observational constraints and no plausible identification can at this point be presented.
Key words: ISM: dust, extinction - ISM: molecules - infrared: ISM: lines and bands - stars: pre-main-sequence - stars: individual: NGC 7538: IRS9
* ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.
Last change: December 16, 1996