Up: Star formation history of environments
Long slit spectra have been obtained, during three different runs, at
the 1.5 m ESO telescope (La Silla). The telescope was equipped with a
Boller & Chivens spectrograph and a UV coated CCD Fa2048L
camera. Parameters of the observations and range of the
variations of the seeing for each run are reported in Table 4.
Table 5 details: the
object identification (1), the observing run (2), the slit position
angle (oriented NE) (3), the exposure time (4), the spectrum quality
(5) and the galaxy portion enclosed in 5
in terms of equivalent
diameter
(i.e. the diameter enclosing half of the total
light) (6). The quality of the spectrum is defined as the average S/N
(Å-1) ratio in the wavelength range 4000 Å- 5000 Å. Higher
S/N spectra are indicated with 3 (S/N > 20) while lower ones are
indicated with 1 (
). Galaxies observations were split
into multiple exposures (typically three) in order to perform cosmic
rays cleaning by a median average among the frames. The slit has been
oriented along the major axis for almost all the objects. Some
pairs have been observed along the line connecting the nuclei.
He-Ar lamps were taken before and after each
exposure to allow an accurate wavelength calibration.
Each frame has been treated separately. Pre-reduction, wavelength
calibration and sky subtraction have been performed using the IRAF
package. Relative flux calibration has been obtained with the use of
a sequence of standard stars. Comparing calibrated stellar spectra
common to different nights and different runs, we estimate that the
flux uncertainty is about 1.0% for data relative to the run n.1, about
0.4% for those relative to the run n.2 and 3.5% for those relative to
the last run.
Before being calibrated in flux, frames have been corrected for the atmospheric
extinction (using the ESO La Silla coefficients) and for the Galactic
extinction (using the values of E(B-V) from
Burstein & Heiles 1982).
Multiple spectra, relative to the same object, have then been
co-added: their alignment was better than 0.5 pixel.
From each flux calibrated spectrum, the portion corresponding to the
central 5
of the galaxy nucleus has been extracted and co-added
producing a one dimensional spectrum. Objects spectra have been
convolved with a gaussian curve (
= 3.37 Å) in order to
degrade their resolution up 8.2 Å (FWHM), to match the Lick-IDS
data resolution (see Sect. 4).
Up: Star formation history of environments
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