Astronomy and Astrophysics Letters dedicated to ISO

The 6.0 and 6.8 micron absorption features in the spectrum of NGC 7538 : IRS9

W. A. Schutte, A. G. G. M. Tielens, D. C. B. Whittet, A. Boogert, P. Ehrenfreund, Th. de Graauw, T. Prusti, E. F. van Dishoeck, P. Wesselius


Short Wavelength Spectrometer observations of the 6.0 and 6.8 micron absorption features towards the obscured young stellar object NGC 7538 : IRS9 are presented and compared to the features of a number of species the bulk of the 6 micron band, additional absorption is required near 5.83 microns and 6.25 microns. 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 micron band are reviewed. Unfortunately, none of these appears to satisfy the observational constraints and no plausible identification can at this point be presented.

ISM: dust, extinction - ISM: molecules - Infrared: ISM: lines and bands - stars: pre-main-sequence - Stars: individual: NGC 7538 : IRS9

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