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Astron. Astrophys. 324, 485-489 (1997)

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2. Observations and data reduction

The spectroscopic observations of UGC 10205 were carried out on March 19-21, 1996 at the Isaac Newton Telescope (INT) in La Palma using the Intermediate Dispersion Spectrograph (IDS).

The H1800V grating with 1800 grooves [FORMULA] was used in the first order in combination with a [FORMULA] [FORMULA] [FORMULA] slit, the 500 mm camera and the AgRed collimator. It yielded a wavelength coverage of [FORMULA] Å between 6650 Å and 6890 Å with a reciprocal dispersion of 9.92  [FORMULA]. We checked that the measured FWHMs do not depend on wavelength and we found a mean value of FWHM = 0.86 Å (i.e. [FORMULA]  Å) that, in the range of the observed gas emission lines, corresponds to [FORMULA]   [FORMULA]. No on-chip binning was done on the adopted 1024 [FORMULA] 1024 TK1024A CCD. Each 24 µ[FORMULA]  24 µm image pixel corresponds to 0.24 Å  [FORMULA].

We took two separate major axis spectra (P.A. = [FORMULA]) for a total exposure time of 100 minutes (Fig. 1). The slit was centered visually on the galaxy nucleus. A comparison copper-argon lamp exposure was obtained between the two object integrations. All the images were reduced using standard MIDAS routines. Considering a sample of 8 bright OH night-sky emission lines, we found a mean deviation from the theorical predicted wavelength (Osterbrock & Martel, 1992) corresponding to [FORMULA]   [FORMULA].

[FIGURE] Fig. 1. UGC 10205 major axis 100 minutes spectrum in the H [FORMULA] region after removal of sky and stellar continuum. Note the multiple-peaked emissions of the H [FORMULA] and the [N II] ([FORMULA] Å) lines in the central regions of the spectrum ([FORMULA])

The gas velocities and velocity dispersions for [FORMULA], where the ionized gas emission lines have a Gaussian profile shape, were derived by means of the MIDAS package ALICE. We measured the H [FORMULA] and the [N II] ([FORMULA] Å) lines, where they were clearly detected. The position, the FWHM and the uncalibrated flux of each emission line were individually determined by interactively fitting one Gaussian plus a polynomial to each emission and to its surrounding continuum. The wavelength of the Gaussian center was converted to the velocity [FORMULA], and then an heliocentric correction of [FORMULA] [FORMULA] was applied. The Gaussian FWHM was corrected for the instrumental FWHM and then converted to the velocity dispersion [FORMULA]. The ionized gas emission lines are double-peaked for [FORMULA] [FORMULA] and even triple-peaked for [FORMULA] [FORMULA]. They have been fitted using the above package with two or three Gaussians respectively and a polynomial continuum. At each radius this multiple-Gaussian fit has been done separately for each emission line.

The gas velocity curves and the velocity dispersion profiles independently derived from the H [FORMULA] (Fig. 2) and the [N II] (Fig. 3) lines are in good agreement at all radii. The kinematical data from H [FORMULA] and [N II] lines are given in Table 1 and in Table 2 respectively. Each table provides the radial distance from the galaxy center r in arcsec (col. 1), the observed heliocentric velocity v (col. 2) and the velocity dispersion [FORMULA] (col. 3) in [FORMULA], the number n of spectrum rows binned along the spatial direction to improve the signal-to-noise ratio of the emission lines (col. 4) and the identification i of the kinematically distinct gas components (col. 5).

[FIGURE] Fig. 2. UGC 10205 major-axis H [FORMULA] kinematics: observed heliocentric velocity curve (top) and velocity dispersion profile (bottom) of the gaseous fast-rotating (crosses), slow-rotating (open triangles), and third (open squares) component. The open circles are used where H [FORMULA] was fitted using a single Gaussian. The velocity dispersion [FORMULA] is plotted with a different spatial binning than v. The dash-dotted and the short-dashed lines connect [FORMULA] values of the fast and the slow-rotating components respectively
[FIGURE] Fig. 3. Same as Fig. 2 for the [N II] ([FORMULA] Å) emission line


Table 1. UGC 10205 major axis H [FORMULA] kinematics


Table 2. UGC 10205 major axis [N II] kinematics

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998