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Astron. Astrophys. 351, 140-146 (1999)

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2. Observations

We undertook a photometric study of the IR emission of the three IRAS galaxies Mkn 496, Mkn 1116 and NGC 6000 with ISOPHT (Lemke et al. 1996). Observations include spectro-photometry in the wavelength range from 2.5 to 11.5 µm and far IR photometry between 120 and 200 µm using the observing templates P-40 and P-22 (Klaas et al. 1994). P-40 observations were performed with both detectors of the PHOT-S subsystem in triangular chopper mode. This mode implies chopping at two reference positions (OFF1, OFF2) and two ON-source measurements. An observing cycle consists of an OFF1-ON-OFF2-ON measurement scheme. The total on-source integration time is 512s. A chopper throw of 30" was adopted. We present P-22 observations of the C200 detector in filters at 120, 150, 180 and 200 µm, an integration time of 16s each, and rectangular chopping. We exclude P-22 chopped observations with the C100 detector because of yet unsolved technical problems. We mention that Mkn 496 = NGC 6090 had already been observed with ISO by Acosta-Pulido et al. (1996) and their C200 and P-40 spectra agree very well with ours.

Data were reduced with PIA (Version 7) 1. The basic calibration steps are detailed in the ISOPHT Data User Manual (Laureijs et al., 1998). In addition, we smooth P-40 spectra by rebinning two neighboring points into one and color correct P-22 data by assuming a spectral shape [FORMULA]. The photometric uncertainty of P-22 chopped observations using PIA 7 calibration files is presently still large ([FORMULA]40%), but it is expected that the accuracy of the photometry will be improved once we better understand the detector and have up-dated calibration files.


Table 1. ISO chopped photometry with the C200 detector. All measurements have a signal-to-noise ratio greater than 10. The errors account for the large calibration uncertainty of [FORMULA]40%. Fluxes are color-corrected and in Jy.

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© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999