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1. Introduction

Fairall-9 (F-9 = ESO 113-IG45) is a Seyfert 1 galaxy (tex2html_wrap_inline4445) in the Southern Hemisphere (tex2html_wrap_inline4447 and tex2html_wrap_inline4449) at z=0.0461 (Ward & Wilson 1978). It was discovered spectroscopically as a Seyfert 1 galaxy by Fairall (1977), who noted its high luminosity of tex2html_wrap_inline4453 and classified it as an extreme Seyfert 1 galaxy, almost a QSO (Fairall 1977; Ward & Wilson 1978; West et al.\ 1978). Its morphology shows an unresolved nucleus (tex2html_wrap_inline4455 at tex2html_wrap_inline4457, taking tex2html_wrap_inline4459) with an envelope with several spiral arms extending until tex2html_wrap_inline4461 from the center and an elliptical companion galaxy at 28'' SE. The diameter of the outer envelope is 64'' (40 kpc), and a jet is suggested to exist out to tex2html_wrap_inline4467 SE of the nucleus (West et al.\ 1978). Griersmith & Visvanathan (1979) classified it as an early type spiral galaxy, but Véron-Cetty et al.\ (1991) consider it an elliptical giant galaxy. Its optical linear polarization is low, tex2html_wrap_inline4469, as in most Seyfert galaxies, consistent with interstellar polarization by dust from our galaxy only (Martin et al.\ 1983).

F-9 has displayed an unusually large amplitude in its variability: it decreased in brightness from 1978 to 1984 with tex2html_wrap_inline4471 and in the UV with tex2html_wrap_inline4473, corresponding to maximum to minimum brightness ratio tex2html_wrap_inline4475 (Wamsteker et al. 1985) and increased afterwards, but never recovered its discovery brightness. Similar variations have been observed in the NIR (Glass 1986; Clavel et al. 1989) and X-rays (Morini et al. 1986), but with smaller amplitude than that seen in the UV. The optical variations between 1979 and 1990 have been extensively documented by Lub & De Ruiter (1992). More recent X-ray observations have been made with GINGA (Makino, private communication) and ROSAT (Walter et al. 1995). FIR observations with IRAS have been reported by Edelson & Malkan (1987) and radio observations by Véron-Cetty et al. (1991).

The emission lines have been studied in considerable detail. The narrow lines of tex2html_wrap_inline4477, have been suggested to show a blue asymmetry in the profile (Whittle 1985; Busko & Steiner 1988, 1989) and no flux variability (Kollatschny & Fricke 1985; Wamsteker et al.\ 1985; Lub & De Ruiter 1992). On the other hand, the intensity and profiles of the broad lines are highly variable. The broad UV lines (tex2html_wrap_inline4479, tex2html_wrap_inline4481  and tex2html_wrap_inline4483) have been extensively studied by Chapman et al.\ (1985), Wamsteker & Colina (1986) and Clavel et al.\ (1989), and the optical lines by Wamsteker et al. (1985) and Lub & De Ruiter (1992). The complex structure of the UV line profiles has been discussed by O'Brien & Zheng (1990) and Zheng & O'Brien (1990). A detailed profile decomposition by means of gaussian components has been made for tex2html_wrap_inline4485\ by Wamsteker et al. (1985). Cross correlation studies of the total intensity of tex2html_wrap_inline4487, tex2html_wrap_inline4489 and tex2html_wrap_inline4491 showed a delay in the line response to UV continuum variation of tex2html_wrap_inline4493 for all three lines (Clavel et al. 1989). Koratkar & Gaskell (1989) suggest that CIV seems to show evidence of infall motion, while tex2html_wrap_inline4495 suggests random motion. Photoionization model calculations on the total line intensities by Clavel & Santos-Lleó (1990) indicate a Broad-Line-Region (BLR) at 100 light-days from the ionizing source, which needs a cut-off energy of 0.83 ryd in the big blue bump, a density of tex2html_wrap_inline4497 and a column density of tex2html_wrap_inline4499 to be able to explain the Wamsteker-Colina effect, the apparent saturation of CIV at high luminosities as defined by Shields et al.\ (1995). Binette et al.\ (1989) require a similar cut-off energy at 0.73 ryd using a different photoionization code.

We discuss here all observations made in the UV (Sect. 2) and compare these with the observations made at other wavelengths to derive the Spectral Energy Distribution (SED) in Sect. 3. In Sect. 4 we give a detailed analysis of the emission line variability, including line decomposition. Section 5 combines the results of Sects. 3 and 4 to compare the data with photoionization calculations and derive the nature of the Broad-Line-Region (BLR) in Sects. 6 and 7. A summary of the results is given in Sect. 8.


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