High-resolution spectral studies were undertaken at orbital phases () 0, 0.25, and 0.5 on the high-mass X-ray binary Vela X-1 using archival Chandra data. We present (1) the first detailed analysis of the multiple strong narrow emission lines present in = 0.5, (2) an analysis of the absorption of the continuum in = 0.5, and (3) the first detection of narrow emission and absorption lines in = 0.25. Multiple fluorescent and H-and He-like emission lines in the band 1.6-20 8 in eclipse are partially obscured at = 0.25 by the X-ray continuum. The = 0.25 spectrum displays three triplets, two with a blueshifted resonance line in absorption and the intercombination and forbidden lines in emission, and shows in absorption other blueshifted lines seen in emission in eclipse. At = 0.5 the soft X-ray continuum diminishes revealing an ''eclipse-like'' spectrum; however, line flux values are around 13-fold those in eclipse. We conclude the narrow emission lines in Vela X-1 become apparent when the continuum is blocked from the line of sight, either by eclipse or by scattering and/or absorption from a wake or cloud. The H-and He-like lines arise in warm photoionized regions in the stellar wind, while the fluorescent lines (including a Ni K line) are produced in cooler clumps of gas outside these regions. Absorption of the 5-13 8 continuum at = 0.5 may be caused by an accretion wake composed of dense stagnant photoionized plasma inside a Stromgren zone. Multiple fluorescent emission lines may be a common feature of the supergiant category of HMXBs.

This paper reports Very Large Array observations at 325 and 1425 MHz (λ90 cm and λ20 cm) during and near the periastron passage of HD 80606b on HJD 2454424.86 (2007 November 20). We obtain flux density limits (3σ ) 18 erg s −1 . The motivation for these observations was that the planetary magnetospheric emission is driven by a stellar wind-planetary magnetosphere interaction so that the planetary luminosity would be elevated near periastron. We estimate that, near periastron, HD 80606b might be as much as 3000 times more luminous than Jupiter. Recent transit observations of HD 80606b provide reasonably stringent constraints on the planetary mass and radius, and, because of the planet's highly eccentric orbit, its rotation period is likely to be "pseudo-synchronized" to its orbital period, allowing a robust estimate of the former. Consequently, we are able to make relatively robust estimates of the emission frequency of the planetary magnetospheric emission and find it to be around 60-90 MHz. While this is too low for our reported observations, we compare HD 80606b to other high-eccentricity systems and assess the detection possibilities for both near-term and more distant future systems. Of the known high-eccentricity planets, only HD 80606b is likely to be detectable, as the others (HD 20782B and HD 4113) are both lower mass and longer rotational periods, which imply weaker magnetic field strengths. We find that both the forthcoming "EVLA low band" system, which will operate as low as 65 MHz, and the Low Frequency Array may be able to improve upon our planetary luminosity limits for HD 80606b, and do so at a more optimum frequency. If the low-frequency component of the Square Kilometre Array (SKA-lo) and a future lunar radio array are able to approach their thermal noise limits, they should be able to detect an HD 80606b-like planet, unless the amount by which the planet's luminosity increases is substantially less than the factor of 3000 that we estimate; for the SKA-lo, which is to be located in the southern hemisphere, future planetary surveys will have to find southern hemisphere equivalents of HD 80606b.

We have observed the type 1.5 Seyfert galaxy NGC 7213 with the Australian Long Baseline Array (LBA) at 8.4 GHz to discover whether this object has the high brightness temperature compact core suggested by low‐frequency variability. Confirmation would support the hypothesis that radio‐intermediate Seyfert galaxies have Doppler‐boosted radio jets. Our observation confirms the existence of this core but with a flux density of almost a factor of 6 less than observed 12 yr earlier. Though few studies exist on the long‐term radio variability of Seyferts, a decline of this magnitude does appear to be rare.

We report the results of a globally coordinated photometric campaign to search for transits by the P ∼ 30 d and P ∼ 60 d outer planets of the 3-planet system orbiting the nearby M-dwarf Gl 876. These two planets experience strong mutual perturbations, which necessitate use of a dynamical (four-body) model to compute transit ephemerides for the system. Our photometric data have been collected from published archival sources, as well as from our photometric campaigns that were targeted to specific transit predictions. Our analysis indicates that transits by planet "c" (P ∼ 30 d) do not currently occur, in concordance with the best-fit i = 50 • co-planar configuration obtained by dynamical fits to the most recent radial velocity data for the system. Transits by planet "b" (P ∼ 60 d) are not entirely ruled out by our observations, but our data indicate that it is very unlikely that they occur. Our experience with the Gl 876 system suggests that a distributed ground-based network of small telescopes can be used to search for transits of very low mass M-stars by terrestrial-sized planets.

The rainfall‐runoff relation was expressed by the convolution integral. The kernel function was evaluated by the Fourier and Laplace gamma transforms and by the direct method. Three analytical examples (known kernels) were analyzed and used to compare the effectiveness of these methods. The Fourier transform method was used for field data. The results indicated that for a third of the storms oscillatory kernels were obtained. Oscillations were not necessarily due to nonlinearities but could arise from random noise in the data. Low‐pass digital filtering of input (excess rainfall) and output (direct runoff) eliminated the kernel oscillations in most cases. The cutoff frequency was approximately the sampling frequency. Accurate output reproduction was obtained by convolution of the original kernel, the smoothed kernel, or the kernel resulting from the filtered data.