2. Observations and data reduction
The spectroscopic observations of NGC 4672 were carried out at the European Southern Observatory in La Silla during three different runs. We observed the galaxy at the Danish 1.54-m telescope on July 12, 1998 and at the ESO 1.52-m telescope on August 6, 1998 and on June 9-10, 1999 respectively.
The Danish 1.54-m telescope was equipped with the Danish Faint Object Spectrograph and Camera (DFOSC). We used the grism No. 7 with 600 grooves and the Loral/Lesser C1W7 CCD, which has pixels of . We took six separate spectra of 30 minutes each along the minor axis of the galaxy () for a total exposure time of 3 hours. To position the slit on the galaxy center an acquisition image of 300 s was obtained in the R band using the ESO filter No. 452.
The Cassegrain Boller & Chivens spectrograph was mounted at the ESO 1.52-m telescope in combination with the grating No. 33 with 1200 grooves and the Loral/Lesser CCD No. 39 with pixels of . We obtained a single 60-minutes spectrum and 4 separate spectra of 60 minutes along the galaxy major axis () in August 1998 and June 1999, respectively.
Every night a number of spectra of late-G and early-K giant stars were obtained to be used as template in measuring the stellar kinematics. Comparison spectra were taken before every object exposure. Further details of the instrumental set-up in the three observing runs are given in Table 1.
Table 1. Instrumental set-up of spectroscopic observations
Using standard ESO-MIDAS 1 routines all the spectra were bias subtracted, flatfield corrected, cleaned from cosmic rays and calibrated. The spectra taken along the same axis in the same run were co-added using the center of the stellar continuum as reference. The contribution of the sky was determined from the edges of the resulting spectra and then subtracted.
The stellar kinematics was measured from the absorption lines present in the spectra using the Fourier Correlation Quotient Method (Bender 1990) as applied by Bertola et al. (1996). The values obtained for the stellar kinematics along the major and minor axis are reported in Tables 3 and 4, respectively. The ionized-gas kinematics was measured from the H and [N II ] emission lines by means of the MIDAS package ALICE as done by Corsini et al. (1999). The gas velocity and velocity dispersion are the mean values obtained from the two emission lines. No error is given when only one velocity or velocity dispersion measurement is available. The kinematical data derived for the gaseous component along the major and minor axis are given in Tables 5 and 6, respectively.
The band acquisition image (Fig. 2) was bias subtracted and flatfield corrected. No attempt was made to perform an absolute calibration since the image was obtained under non-photometric condition.
© European Southern Observatory (ESO) 2000
Online publication: August 17, 2000