Astron. Astrophys. 342, 87-100 (1999)

2. Observations and data reduction

Long slit optical spectra were collected at the ESO NTT telescope in March 1995 using a dichroic beam splitter feeding both blue (1024² Tek-CCD with /pix) and red (2048² Tek-CCD with /pix) arms of EMMI. Simultaneous blue (3700-5000 with 1.7 Å/pix) and red (5000-10000 with 1.2 Å/pix) spectra were obtained through a slit centered on the optical nucleus at two position angles (cf. Fig. 1). The first was at PA=, roughly aligned with the [OIII] cone axis and including the brightest [OIII] emitting knots, while the second was at PA= and along the low excitation rim visible in the [SII] and "true colour" images shown in Fig. 5 and Fig. 10 of M94, ¹. Several exposures were averaged and the total integration times of the spectra at PA= were 100, 75, 25 minutes over the 3700-5000, 5000-7300 and 7700-10080 Å wavelength ranges, respectively. The spectra at PA= covered 3700-5000 and 5000-7300 Å with a total integration time of 50 minutes per wavelength interval. Data were flux calibrated using observations of LTT3218 and reduced with MIDAS using standard procedures.

Fig. 1. Slit positions overlaid on grey-scale line images. The positions of the various knots are marked.

Infrared spectra were collected in March 1995, also at the ESO NTT using the spectrometer IRSPEC equipped with a 62x58 SBRC InSb array whose pixel size was along the slit and 5 Å along the dispersion direction. Spectra of [FeII]1.644 µm, H₂ 2.121 µm, Br and [SiVI]1.962 µm were obtained using a slit at PA=. Each long-slit spectrum consisted of 4 ABBA cycles (A=source, B='sky', i.e. a region E) with 2x60 sec integrations per position. The data were reduced using the IRSPEC context of MIDAS which was developed by one of us (EO) and which also allows the accurate subtraction of time variable OH sky lines. The same airglow emission was used as wavelength reference (Oliva & Origlia 1992) and the spectra were corrected for instrumental and atmospheric transmission using spectra of featureless early O stars and flux calibrated using measurements of photometric standard stars.

© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998
helpdesk.link@springer.de