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Astron. Astrophys. 338, L91-L94 (1998)

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2. Observations and reductions

Spectroscopic observations was performed using a Boller & Chivens cassegrain spectrograph at 1.52m ESO telescope of La Silla (Chile). A UV-flooded thinned Loral Lesser CCD #39 (2048 x 2048, 15µm/pixel) detector was used.

Two gratings, with different dispersions, were used. One grating, with 600 l/mm which has a reciprocal dispersion of 1.9 Å pixel-1 and with a resolution of 4.6 Å, was used for spectral coverage between 3500 Å and 7500 Å. The other grating, with 1200 l/mm which has a reciprocal dispersion of 1.0 Å pixel-1, with a resolution of 2.0 Å was used for spectral coverage between 3100 Å and 5100 Å. The slit width was 4 arcsec. The slit orientation in the blue range was aligned with the parallactic angle in order to minimize the slit loss due to atmospheric refraction. Table 1 shows the log of observations and the typical S/N noise ratio in the continuum achieved in each observation.


[TABLE]

Table 1. Observation log of SPH 2.


The data were reduced to the linear scale, i.e. wavelength versus flux, using IRAF. The data were treated with the help of the ccdproc and onedspec tasks of IRAF. We followed the standard procedure consisting of bias subtraction, flat-field normalization and wavelength calibration through a He-Ar lamp. Counts were corrected from atmospheric extinction and calibrated from instrumental chromatic response through observations of standard stars from Oke (1974) and from Hamuy et al. (1994). In the linearized spectra, the line fluxes were measured with the splot task and blends were resolved using the deblend option. Figs. 1 and 2 show the reduced spectra of our sample. We estimate the errors in the fluxes to be about 20% for weaker lines (line fluxes [FORMULA]10 on the scale of H[FORMULA]=100) and about 10% for stronger lines. No significant line flux variations was detected in our observations performed at November 1997 and at January 1998.

[FIGURE] Fig. 1. Blue spectrum of SPH 2. Notice the strength of He II at 4686 Å. Also notice the diffuse absorption band at 4430 Å.

[FIGURE] Fig. 2. Optical spectrum of SPH 2. Notice the strength of C IV [FORMULA]5808 Å. Also notice the diffuse absorption bands at 6284 Å. The emission line at 5577 Å is the night-sky [O I ].

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© European Southern Observatory (ESO) 1998

Online publication: September 17, 1998
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