Astron. Astrophys. 339, 327-336 (1998)

2. The optical spectrum

Optical spectra of 1H0419-577 were obtained at the ESO 1.52m telescope on 1996 October 1 and 2, using the Boller & Chivens spectrograph with a 127mm camera and a Loral/Lesser thinned CCD with pixels. The pixel size is , and the projected scale on the detector 0.82 arcsec pixel^-1. The grating used has 600 grooves mm^-1. The spectra were obtained through a 2-arcsec wide slit, at a resolution of 4.6 Å. Both nights were photometric. Two integrations of 1800 seconds each were obtained.

Standard techniques were used to reduce the spectra, using the NOAO IRAF package. In particular, the spectrophotometric calibration of the spectra was perfected through their comparison with, and broad-band normalized to, short exposures of 1H0419-577 obtained during the same nights through an 8 arcsec slit. This allowed us to correct the narrow-slit spectra for light losses and differential refraction. The two spectra were averaged and yielded the final spectrum shown in Fig. 1. Because the calibration curves of the two nights and the individual spectra coincide within %, we consider the spectrophotometric quality of the final spectrum to be of this order.

Fig. 1. The optical spectrum of 1H0419-577 obtained in 1996 October. The spectrum has been displayed in two parts for clarity, and the red part (bottom panel) is also shown magnified by a factor 8 to enhance the weaker lines. The main optical lines are indicated on the plot. The wavelength scale is in the rest system of the observer (z=0.103).

The spectrum displays characteristics typical of Seyfert 1 galaxies, with strong broad permitted lines and narrow forbidden lines. Table 1 lists the fluxes, equivalent widths, and FWHM of the main lines. In order to obtain these measurements a 1st order pseudo-continuum was fitted to the local minima bracketing each line. In most permitted lines the broad component was isolated by modeling the narrow line contribution with a suitably scaled profile of the [O III]5007 line. Each scaling factor was determined on the basis of the smoothest residual broad profile. The corresponding line fluxes in Table 1 are thus simply the [O III]5007 flux multiplied by the respective scaling factors. In addition, the contaminating lines were subtracted from H and H using a scaled [O III]5007 profile for the narrow lines ([O III]4959, [N II]6548 and 6584) and a scaled broad-H profile for the broad lines (He II 4686 and Fe II 4924). The Fe II lines are weaker than average for a Seyfert 1: the ratio between the integrated fluxes of the 4570 Å (rest wavelength) blend and of H is lower than 0.1 (cfr. Joly 1988).

Table 1. Integrated fluxes, FWHM, and equivalent widths of the main optical emission lines

The spectrum is in broad agreement with the one presented by Brissenden (1989) and confirms unambiguously the classification of 1H0419-577 as a Seyfert 1.

© European Southern Observatory (ESO) 1998

Online publication: October 21, 1998
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