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Astron. Astrophys. 323, 697-706 (1997)

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Dust extinction of H II regions in NGC 598 and NGC 5457 *

L. Petersen and P. Gammelgaard

Institut for Fysik og Astronomi, Aarhus Universitet, Ny Munkegade, DK-8000 Å rhus C, Denmark

Received 10 July 1996 / Accepted 4 December 1996


The dust extinction towards bright H II regions in NGC 598 and NGC 5457 has been studied in detail by forming line ratios of Balmer and Paschen emission lines covering a large wavelength range. Three homogeneous models of the geometrical distribution of the emitting sources and the obscuring dust have been tested. Only for low extinctions can the data be fit by a homogeneous slab. For most of the observed H II regions  the Witt et al. (1992) 'dusty nucleus' model matches the observations equally well as the usual assumption of a foreground screen, but the former implies much larger actual dust contents. Spatial variations in the optical depth in V of the order 0.3 across a region are found.

Key words: galaxies: NGC 598; NGC 5457 – galaxies: ISM – dust, extinction – H ii regions

* Based on observations collected at the Nordic Optical Telescope, La Palma, Spain

Send offprint requests to: larsp@obs.aau.dk

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998