| 1. |
- Clavel, J., et al.
(författare)
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Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. I. An 8 month campaign of monitoring NGC 5548 with IUE
- 1991
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 366:1, s. 64-8181
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Tidskriftsartikel (refereegranskat)abstract
- The authors present emission-line and ultraviolet continuum observations of a type I Seyfert galaxy in which the time resolution is adequate for describing the character of variability. Using the IUE satellite, the nucleus of NGC 5548 was observed every 4 days for a period of 8 months. Its mean properties-continuum shape, line ratios-are not unusual for type I Seyfert galaxies, but it was found to be strongly variable. The ultraviolet continuum flux and broad emission line fluxes varied significantly, going through three large maxima and three deep minima. The great majority of all variations were well resolved in time. The data lend qualitative support to the view that photoionization by the nuclear continuum is responsible for driving the emission lines
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| 2. |
- Penston, M. V., et al.
(författare)
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The extended narrow line region of NGC 4151. I. Emission line ratios and their implications
- 1990
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 236:1, s. 53-6262
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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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| 3. |
- Dietrich, M., et al.
(författare)
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Monitoring of active galactic nuclei. IV. The Seyfert 1 galaxy NGC 4593
- 1994
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 284:1, s. 33-4343
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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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| 4. |
- Wanders, I., et al.
(författare)
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Spectroscopic monitoring of active galactic nuclei. II. The Seyfert-1 galaxy NGC 3516
- 1993
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 269:1-2, s. 39-5353
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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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| 5. |
- Stirpe, G. M., et al.
(författare)
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Monitoring of active galactic nuclei. V. The Seyfert 1 galaxy Markarian 279
- 1994
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 285:3, s. 857-867867
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Tidskriftsartikel (refereegranskat)abstract
- For pt. IV see ibid., vol.284, no.1, p.33-43 (1994). Reports on the Lovers of Active Galaxies' (LAG) monitoring of the Seyfert 1 galaxy Markarian 279 from January to June 1990. The source, which was in a very bright state, gradually weakened after the first month of monitoring: the Halpha and Hbeta flux decreased by 20% and 35% respectively, and the continuum under Halpha by 30%. The luminosity-weighted radius of the broad line region (BLR), as derived from the cross-correlation function, is of the order of 10 light days. This result is very uncertain because the features in the light curves are very shallow, but it is unlikely that the radius of the BLR is more than 1 light month. The profile variations of Halpha confirm that the prevailing motions are not radial. The data of the present campaign and those obtained in previous years, when the source was in a much weaker state, show that the red asymmetry of the Balmer lines correlates positively with the broad line flux. This new effect is briefly discussed
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| 6. |
- Hillarp, A, et al.
(författare)
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The human C4b-binding protein beta-chain gene
- 1993
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Ingår i: The Journal of biological chemistry. - 0021-9258. ; 268:20, s. 23-15017
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Tidskriftsartikel (refereegranskat)abstract
- Human complement component C4b-binding protein (C4BP) is composed of seven alpha-chains and one beta-chain. The alpha- and beta-chains are homologous and both contain multiple copies of short consensus repeats (SCR) and in addition carboxyl-terminal non-repeat regions. Each of the alpha-chains contains a binding site for C4b, whereas the beta-chain binds protein S, a vitamin K-dependent protein involved in the regulation of blood coagulation. The alpha- and beta-chain genes are closely linked in the regulators of complement activation gene cluster on the long arm of human chromosome 1, band 1q32. The human beta-chain gene which has now been characterized was found to span more than 10 kilobases of DNA. The presence of at least two different beta-chain gene transcripts was suggested by the isolation of two new cDNA clones which contained different sequences in their extended 5'-untranslated regions. Northern blot analysis demonstrated that the two clones represented distinct beta-chain mRNAs with different 5' end sequences. One class of beta-chain mRNA (denoted A19) was found to be encoded by six exons and primer extension, and S1 nuclease protection assays revealed multiple closely spaced transcription start sites for this mRNA class. Its 5'-untranslated region and signal peptide was encoded by the first exon. The second class of mRNA (denoted A12) had a different transcription start site and its 5'-untranslated region was derived from at least three exons out of which the last one was formed by utilization of an acceptor splice site within the first A19 exon. Exons encoding the mature beta-chain and the 3'-untranslated region were common to both classes of mRNA. The beta-chain contains three SCRs, out of which the first and second are encoded by individual exons, whereas two exons encode the third SCR. The exon encoding the carboxyl-terminal part of the third SCR also encodes 14 amino acids of the non-repeat region. The last exon encodes the remaining 46 carboxyl-terminal amino acids and the entire 3'-untranslated region. The elucidation of the organization of the beta-chain gene provides insight into the sophisticated molecular structure of C4BP and a basis for future structural and functional studies.
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