Astron. Astrophys. 315, L289-L292 (1996)
SWS observations of IR emission features towards compact HII regions*
P.R. Roelfsema1,4, P. Cox2, A.G.G.M. Tielens3, L.J. Allamandola3, J.-P. Baluteau5, M.J. Barlow6, D. Beintema1,4, D.R. Boxhoorn1,4, J.P. Cassinelli7, E. Caux8, E. Churchwell7, P.E. Clegg9, Th. de Graauw1, A.M. Heras4, R. Huygen10, K.A. van der Hucht11, D.M. Hudgins3, M.F. Kessler4, T. Lim4,9, and S.A. Sandford3
1 SRON, P.O. Box 800,
9700 AV Groningen, The Netherlands
Received 31 July 1996 / Accepted 29 August 1996
Abstract. We present ISO Short Wavelength Spectrometer (SWS**) grating spectra of six compact HII regions. In addition to strong emission lines from atomic species these spectra display infrared bands attributed to Polycyclic Aromatic Hydrocarbons (PAHs). The continuous spectral coverage of the present observations and the high spectral resolution allow to describe the detailed structure of the emission bands: the 7.7 band is composed of two bands at 7.6 and 7.8 , the 6.2 band has a long wavelength extension, there is a plateau of emission between 6 and 7 and a new feature is reported at 11.0 in addition to the well-known 11.2 band. These observations also reveal large variations in the relative intensities of the dust bands, in particular between the 7.7 and 8.6 bands. In one extreme case, the 8.6 band is stronger than the 7.7 band. These observations are compared to a mixed population of ionized PAHs, using new laboratory measurements.
Key words: ISM: dust - ISM: HII regions - ISM: molecules - infrared: ISM: lines and bands
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 the
participation of ISAS and NASA.
Last change: December 16, 1996