Astron. Astrophys. 333, L75-L78 (1998)

2. Observations and data reduction

Observations of a variety of starburst galaxies in the [O iv], [Ne ii] and [Ne iii] lines have been obtained with the ISO-SWS in 1996 and 1997, as part of a more comprehensive guaranteed time program. In addition, we use data from a raster of SWS observations along the major axis of M 82 obtained on March 16, 1996 in an open time program. One of the target lines of this program was [Fe ii] 25.988 µm, which is close enough in wavelength to extract the [O iv] line from the same scans.

Integration times of our observations in SWS02 mode were typically 2 seconds per step, i.e. 200 seconds for the complete up-down scan covering the line. We used standard procedures from the SWS Interactive Analysis system for data reduction. For strong sources like bright starbursts, residual fringing is often obvious in the processed data. This was corrected for by fitting sine functions to line-free regions of the spectra. This procedure is sufficiently reliable for the brightest sources, since the fringes can be approximated by a single sine function over the small observed wavelength range near [O iv], and the lines are narrow. Nevertheless, baseline uncertainty due to fringing is often the limiting factor in measuring the [O iv] line flux, and allows us to set only upper limits in some sources. [Ne ii] and [Ne iii] were always significantly stronger than residual fringes at these wavelengths.

© European Southern Observatory (ESO) 1998

Online publication: April 28, 1998

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