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Träfflista för sökning "WFRF:(Aretxaga I.) srt2:(1990-1994)"

Sökning: WFRF:(Aretxaga I.) > (1990-1994)

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1.
  • Penston, M. V., et al. (författare)
  • The extended narrow line region of NGC 4151. I. Emission line ratios and their implications
  • 1990
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 236:1, s. 53-6262
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper presents the first results from long-slit spectra of the Seyfert galaxy NGC 4151 which give average diagnostic ratios of weak lines in the extended narrow line region (ENLR) of that galaxy and the first direct density measurement in an ENLR. These data confirm that the ENLR is kinematically undisturbed gas in the disc of the galaxy which is illuminated by an ionizing continuum stronger by a factor of 13 than a power law interpolated between observed ultraviolet and X-ray fluxes. Explanations of this apparent excess include a hot thermal continuum, time variations and an anisotropic radiation field. The authors give reasons for favouring anisotropy which might be caused by shadowing by a thick accretion disc or by relativistic beaming. Shadowing by a molecular torus is unlikely, given the absence of an infrared signal from the reradiated flux absorbed by any torus. Anisotropy would have important implications for the bolometric luminosity and nature of active galactic nuclei
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2.
  • Dietrich, M., et al. (författare)
  • Monitoring of active galactic nuclei. IV. The Seyfert 1 galaxy NGC 4593
  • 1994
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 284:1, s. 33-4343
  • Tidskriftsartikel (refereegranskat)abstract
    • Results of a five-month campaign of optical monitoring the Seyfert 1 galaxy NGC 4593 are presented. High resolution Halpha and Hbeta spectra and direct images in the Johnson U, B, V, R and I bands were obtained between January and June 1990. The emission lines and the continuum showed strong variations on time scales of weeks to days. The Halpha line varied by more than 30% within only 5 days. Cross-correlating the light curves of the Balmer lines with that of the optical continuum gives a lag of around 4 days. Therefore, this low luminosity Seyfert galaxy may have one of the smallest broad line regions known so far
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3.
  • Wanders, I., et al. (författare)
  • Spectroscopic monitoring of active galactic nuclei. II. The Seyfert-1 galaxy NGC 3516
  • 1993
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 269:1-2, s. 39-5353
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors present the results of a five month spectroscopic monitoring campaign of the Seyfert-1 galaxy NGC 3516. Using a new calibration method and applying a correction for seeing differences during the various observations they can scale the spectra to each other with a much higher accuracy than hitherto achieved. NGC 3516 shows large amplitude variations on a time scale of several weeks. Asymmetric profile variations occur on the same time scale as the continuum variations. The authors show the presence of a varying dip on the blue wing of the Hbeta profile, which is not present on the Halpha profile, and which corresponds to the absorption features previously seen in the UV emission lines of NGC 3516. From cross-correlation analysis they find a time lag of 14plusmn2 days for the Halpha and 7plusmn3 days for the Hbeta emission-line response to continuum variations
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