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Astron. Astrophys. 351, 47-58 (1999) 3. Observations and data reductionThe spectroscopic observations were carried out on the nights 1997 July 3-5 and 1998 July 25-27 using the EMMI multi-purpose instrument at the NTT (New Technology Telescope) in La Silla Observatory (ESO-Chile). The observations are described in detail in VMBF99. The data reduction was done using standard methods in IRAF. The
spectra were bias subtracted and divided by a normalized flat-field
frame (dome flat-field). Illumination corrections along the slit were
found to be negligible. The spectra were calibrated in wavelength
using comparison spectra of HeAr. Cosmic rays were removed
automatically (we obtained at least three similar frames for each
object). Sky lines were subtracted and the spectra corrected for
atmospheric extinction with the aid of mean extinction coefficients
for La Silla. For each night we built a mean response curve from the
standard stars observed that night with a wide slit (5 arc sec). Each
object frame was flux calibrated with the corresponding response
curve. The spectra were also corrected for galactic reddening. The
reddening values were based on Burstein & Heiles (1984) maps,
using empirical selective function of Cardelli et al. (1989). The
redshifted CIII] Both IRAF and STARLINK (DIPSO) routines were used to measure the emission line fluxes, FWHMs and wavelengths. 1-D spectra were extracted for all objects from apertures described below. We then fitted Gaussian profiles to the lines. The measured flux and FWHM of the spectral line are the values measured from the fit of the Gaussian. The instrumental profile was subtracted from the observed FWHM in quadrature. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1999 Online publication: November 2, 1999 ![]() |