Bright spot

Abstract: Seismic reflection data were used to monitor the progress of an in‐situ combustion, enhanced oil recovery process. Three sets of three‐dimensional (3-D) data were collected during a one‐year period in order to map the extent and directions of propagation in time. Acquisition and processing parameters were identical for each survey so that direct one‐to‐one comparison of traces could be made. Seismic attributes were calculated for each common‐depth‐point data set, and in a unique application of seismic reflection data, the preburn attributes were subtracted from the midburn and postburn attributes. The resulting “difference volumes” of 3-D seismic data showed anomalies which were the basis for the interpretation shown in this case study. Profiles and horizon slices from the data sets clearly show the initiation and development of a bright spot in the reflection from the top of the reservoir and a dim spot in the reflection from a limestone below it. Interpretation of these anomalies is supported by informa...

Abstract: We present the first detection of the photometric variability in a spectroscopically confirmed Y dwarf. The Infrared Array Camera on board the Spitzer Space Telescope was used to obtain time series photometry of WISE J140518.39+553421.3 at 3.6 and 4.5 μm over a 24-hr period at two different epochs separated by 149 days. Variability is evident at 4.5 μm in the first epoch and at 3.6 and 4.5 μm in the second epoch, which suggests that the underlying cause or causes of this variability change on the timescales of months. The second-epoch [3.6] and [4.5] light curves are nearly sinusoidal in form, in phase, have periods of roughly 8.5 hr, and have semi-amplitudes of 3.5%. We find that a simple geometric spot model with a single bright spot reproduces these observations well. We also compare our measured semi-amplitudes of the second-epoch light curves to predictions of the static, one-dimensional, partly cloudy, and hot spot models of Morley and collaborators, and find that neither set of models can reproduce the observed [3.6] and [4.5] semi-amplitudes simultaneously. Therefore, more advanced two-dimensional or three-dimensional models that include time-dependent phenomena like vertical mixing, cloud formation, and thermal relaxation are sorely needed in order to properly interpret our observations.

Abstract: Here we show that in the case when double peaked emission lines originate from outer parts of accretion disk, their variability could be caused by perturbations in the disk emissivity. In order to test this hypothesis, we introduced a model of disk perturbing region in the form of a single bright spot (or flare) by a modification of the power law disk emissivity in appropriate way. The disk emission was then analyzed using numerical simulations based on ray-tracing method in Kerr metric and the corresponding simulated line profiles were obtained. We applied this model to the observed H-beta line profiles of 3C 390.3 (observed in the period 1995-1999), and estimated the parameters of both, accretion disk and perturbing region. Our results show that two large amplitude outbursts of the H-beta line observed in 3C 390.3 could be explained by successive occurrences of two bright spots on approaching side of the disk. These bright spots are either moving, originating in the inner regions of the disk and spiralling outwards by crossing small distances during the period of several years, or stationary. In both cases, their widths increase with time, indicating that they most likely decay.

Abstract: We present new Very Long Baseline Interferometry (VLBI) images of supernova (SN) 1986J, taken at 5, 8.4, and 22?GHz between t = 22 and 25 yr after the explosion. The shell expands t 0.69?0.03. We estimate the progenitor's mass-loss rate at (4-10) ? 10?5 M ? yr?1 (for v w = 10 km s?1). Two bright spots are seen in the images. The first, in the northeast, is now fading. The second, very near the center of the projected shell and unique to SN 1986J, is still brightening relative to the shell, and now dominates the VLBI images. It is marginally resolved at 22?GHz (diameter ~0.3 mas; ~5 ? 1016 cm at 10 Mpc). The integrated VLA spectrum of SN 1986J shows an inversion point and a high-frequency turnover, both progressing downward in frequency and due to the central bright spot. The optically thin spectral index of the central bright spot is indistinguishable from that of the shell. The small proper motion of 1500 ? 1500 km s?1 of the central bright spot is consistent with our previous interpretation of it as being associated with the expected black-hole or neutron-star remnant. Now, an alternate scenario seems also plausible, where the central bright spot, like the northeast one, results when the shock front impacts on a condensation within the circumstellar medium (CSM). The condensation would have to be so dense as to be opaque at cm wavelengths (~103? denser than the average corresponding CSM) and fortuitously close to the center of the projected shell. We include a movie of the evolution of SN 1986J at 5?GHz from t = 0 to 25 yr.