The 6.0 and 6.8µm absorption features in the spectrum of NGC 7538: IRS9.
Prusti, T.; de Graauw, T.; van Dishoeck, E. F.; Whittet, D. C. B.; Schutte, W. A.; Tielens, A. G. G. M.; Ehrenfreund, P.; Boogert, A.; Wesselius, P.
Abstract
Short Wavelength Spectrometer observations of the 6.0 and 6.8μm 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 H_2_O provides the bulk of the 6μm band, additional absorption is required near 5.83μm and 6.25μm. 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 6.8μm band are reviewed. Unfortunately, none of these appears to satisfy the observational constraints and no plausible identification can at this point be presented.