The spectroscopic observations were performed during dark time on the nights
of February 24 to 26, 1995, using a REOSC spectrograph mounted on
the f/8.48 Cassegrain focus of the CASLEO 2.15 m Ritchey-Chrétien telescope
in El Leoncito (San Juan, Argentina). The seeing was between 2and 3
. The detector was a Tektronix CCD
24
m pixels, corresponding each to 0
26. The exposures were
obtained through a slit of 3
3
348
, on the focal
plane, at the six positions indicated in Fig. 1. Five are at
PA = 40
, which was assumed to be the PA of the line of nodes, and
one along the narrow northern arm, at a PA of 79
. All positions were
referred to the center of the galaxy. Instead of
shifting the slit for each position, the slit was positioned first on the
center and then the telescope was moved in order to bring the
slit to the required position.
In total, there were seven exposures, two of them using a
300 lines mm-1 grating at an angle of 450
, over the
wavelength range of
3500-7000 (positions 3 and 5 in
Fig. 1), and the other five with a 1200 lines mm-1 grating
at an angle of 25
53
, covering the wavelength range of
6200-6900 (positions 1, 2, 3, 4, and 6 in
Fig. 1). The dispersions
were 125 and 32 Å mm-1, the reciprocal dispersions 3.1 and
0.76 Å per pixel and the resolutions 10 and 2.5 Å for the
300 and 1200 lines mm-1 gratings, respectively.
The usual procedure was followed for the observations, including the
observation of the flat field, the comparison spectra and the dark current.
The exposures were, in general, of 20 min and repeated till the total
time indicated in Table 1 was reached for each position.
The spectra were corrected for atmospheric extinction and galactic
reddening (Burstein & Heiles 1984) and the flux was
calibrated with stars from the catalog of Stone & Baldwin
(1982). Data reduction of the spectra was made employing
standard methods of the IRAF (developed by NOAO) reduction package.
Copyright The European Southern Observatory (ESO)