Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XIII. Ultraviolet Observations of the Broad-Line Radio Galaxy 3C 390.3

As part of an extensive multi-wavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31-1996 March 5. Spectra were obtained every 6È10 days. The UV continuum varied by a factor of 7 through the campaign, while the broad emission lines varied by factors of 2È5. Unlike previously monitored Seyfert 1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV continuum light curve is similar in both amplitude and shape to the X-ray light curve observed by ROSAT . The UV broad emission-line variability lags that of the UV continuum by 35È70 days for Lyα and C IV, values larger than those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are also larger than those found for the Balmer lines in 3C 390.3 over the same period. The red and blue wings of C IV and Lyα vary in phase, suggesting that radial motion does not dominate the kinematics of the UV line-emitting gas. Comparison with archival data provides evidence for velocity-dependent changes in the Lyα and C IV line profiles, indicating evolution in the detailed properties and/or distribution of the broad-line emitting gas. Joint Institute for Nuclear Research, Dubna, Russi

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. IX. Ultraviolet Observations of Fairall 9

An 8 month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with the International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuumÈemission-line delays for a high-luminosity active galactic nucleus (AGN). While the results of this campaign are more ambiguous than those of previous monitoring campaigns on lower luminosity sources, we Ðnd general agreement with the earlier results : (1) there is no measurable lag between ultraviolet continuum bands, and (2) the measured emission-line time lags are very short. It is especially notable that the Lyα + N V emission-line lag is about 1 order of magnitude smaller than determined from a previous campaign by Clavel, Wamsteker, & Glass (1989) when Fairall 9 was in a more luminous state. In other well-monitored sources, speciÐcally NGC 5548 and NGC 3783, the highest ionization lines are found to respond to continuum variations more rapidly than the lower ionization lines, which suggests a radially ionization-stratified broad-line region. In this case, the results are less certain, since none of the emission-line lags are very well determined. The best-determined emission line lag is Lyα + N V, for which we find that the centroid of the continuum—emission-line crosscorrelation function is tcent ≈14—20 days. We measure a lag tcent<~4 days for He II λ1640; this result is consistent with the ionization-stratification pattern seen in lower luminosity sources, but the relatively large uncertainties in the emission-line lags measured here cannot rule out similar lags for Lyα + N V and He II λ1640 at a high level of significance. We are unable to determine a reliable lag for C IV λ1550, but we note that the profiles of the variable parts of Lyα and C IV λ1550 are not the same, which does not support the hypothesis that the strongest variations in these two lines arise in the same region

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XI. Intensive Monitoring of the Ultraviolet Spectrum of NGC 7469

From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 2.d3-3.d1 for Lyα, 2.d7 for C IV λ1549, 1.d9-2.d4 for N IV λ 1240, 1.d7-1.d8 for Si IV λ 1400, and 0.d7-1.d0 for He II λ1640. The most remarkable result, however, is the detection of apparent time delays between the different UV continuum bands. With respect to the UV continuum flux at 1315 Å, the flux at 1485 Å, 1740 Å, and 1825 Å lags with time delays of 0.d21, 0.d35, and 0.d28, respectively. Determination of the significance of this detection is somewhat problematic since it depends on accurate estimation of the uncertainties in the lag measurements, which are difficult to assess. We attempt to estimate the uncertainties in the time delays through Monte Carlo simulations, and these yield estimates of ~0.d07 for the 1 σ uncertainties in the interband continuum time delays. Possible explanations for the delays include the existence of a continuum-flux reprocessing region close to the central source and/or a contamination of the continuum flux with a very broad time-delayed emission feature such as the Balmer continuum or merged Fe II multiplets

The C-terminal Region of Mitochondrial Single-subunit RNA Polymerases Contains Species-specific Determinants for Maintenance of Intact Mitochondrial Genomes

Functional conservation of mitochondrial RNA polymerases was investigated in vivo by heterologous complementation studies in yeast. It turned out that neither the full-length mitochondrial RNA polymerase of Arabidopsis thaliana, nor a set of chimeric fusion constructs from plant and yeast RNA polymerases can substitute for the yeast mitochondrial core enzyme Rpo41p when expressed in Δrpo41 yeast mutants. Mitochondria from mutant cells, expressing the heterologous mitochondrial RNA polymerases, were devoid of any mitochondrial genomes. One important exception was observed when the carboxyl-terminal domain of Rpo41p was exchanged with its plant counterpart. Although this fusion protein could not restore respiratory function, stable maintenance of mitochondrial petite genomes (ρ(−))(−) was supported. A carboxyl-terminally truncated Rpo41p exhibited a comparable activity, in spite of the fact that it was found to be transcriptionally inactive. Finally, we tested the carboxyl-terminal domain for complementation in trans. For this purpose the last 377 amino acid residues of yeast mitochondrial Rpo41p were fused to its mitochondrial import sequence. Coexpression of this fusion protein with C-terminally truncated Rpo41p complemented the Δrpo41 defect. These data reveal the importance of the carboxyl-terminal extension of Rpo41p for stable maintenance of intact mitochondrial genomes and for distinct species-specific intramolecular protein–protein interactions