Envelope dynamics of iron-core supernova models

Wilson has found that the neutrino transport mechanisms is unable to generate a supernova explosion in stars with collapsing iron cores. We have utilized Wilson’s analysis to investigate the behavior of the overlying potentially explosive layers which Wilson omitted. The outer boundary of the core of Wilson’s models moves in such a, manner as to deliver a shock to the base of the envelope. We have numerically followed the progress of such shocks into the envelope of a realistic model obtained from evolutionary calculations. We find that only shocks so strong as to be inconsistent with our treatment are capable of ejecting material. For reasonable shocks the nuclear burning does not proceed rapidly at densities below ?～10⁶g cm^?3, and the nuclear energy released is less than the shock energy in all models that come near to ejecting matter. The initial model adopted here, which is based on a particular set of evolutionary calculations and which neglects rotation and magnetic fields, seems destined to generate a black hole. The creation of a black hole in such a way is probably not attended by a supernova explosion.     

Off-center detonations in evolved stellar cores

Recent work on late stages of evolution has raised the possibility that the stars in the mass range from 4–8M _bd may ignite carbon violently off-center. Hydrodynamic evolution has been carried out for models with various central densities and for temperature profiles both with and without an inversion. It has been found that, provided ignition leads to a detonation, both types of presupernova models have essentially the same final post detonation behavior. In particular, an off-center detonation is unable to prevent a complete disruption of the star if ignition occurs at low density.     

Re-appraisal of earthquake catalog in the Pamir―Hindu Kush region,emphasizing the early and modern instrumental earthquake events

Journal of Seismology - The Pamir-Hindu Kush region is seismically the most dynamic and active zone that went through many devastating earthquakes. While much research is ongoing to produce seismic...     

Flare-associated surge prominence on 1980 october 30

The Hα observations of a flare-associated surge prominence on 1980 October 30 have been described. Morphology and dynamics of the surge prominence have been presented. From our observations and analysis we have estimated the magnetic field associated with surge material to be about 35 gauss which is in good agreement with the earlier result of Tandberg-Hanssen & Malville (1974). It has been determined that coronal pressure is not acting as a resistive force on the outward expansion of the surge into the corona. The kinetic energy of the surge was about 10²⁸ erg, which is 2 orders less than required for the mass to escape the chromosphere. It appears that the flare-associated surge prominence was perhaps a result of kink instability in the flaring region.     

Low‐frequency passive seismic experiments in Abu Dhabi,United Arab Emirates: implications for hydrocarbon detection

Low‐frequency passive seismic experiments utilizing arrays of 3‐component broadband seismometers were conducted over two sites in the emirate of Abu Dhabi in the United Arab Emirates. The experiments were conducted in the vicinity of a producing oilfield and around a dry exploration well to better understand the characteristics and origins of microtremor signals (1–6 Hz), which had been reported as occurring exclusively above several hydrocarbon reservoirs in the region. The results of the experiments revealed that a strong correlation exists between the recorded ambient noise and observed meteorological and anthropogenic noises. In the frequency range of 0.15–0.4 Hz, the dominant feature is a double‐frequency microseism peak generated by the non‐linear interactions of storm induced surface waves in the Arabian Sea. We observed that the double‐frequency microseism displays a high variability in spectral amplitude, with the strongest amplitude occurring when Cyclone Gonu was battering the eastern coast of Oman; this noise was present at both sites and so is not a hydrocarbon indicator. Moreover, this study found that very strong microtremor signals in the frequency range of 2–3 Hz were present in all of the locations surveyed, both within and outside of the reservoir boundary and surrounding the dry exploration well. This microtremor signal has no clear correlation with the microseism signals but significant variations in the characteristics of the signals were observed between daytime and nighttime recording periods that clearly correlate with human activity. High‐resolution frequency‐wavenumber (f‐k) spectral analyses were performed on the recorded data to determine apparent velocities and azimuths of the wavefronts for the microseism and microtremor events. The f‐k analyses confirmed that the double‐frequency microseism originates from wave activity in the Arabian Sea, while the microtremor events have an azimuth pointing towards the nearest motorways, indicating that they are probably being excited by traffic noise. Results drawn from particle motion studies confirm these observations. The vertical‐to‐horizontal spectral ratios of the data acquired in both experiments show peaks around 2.5–3 Hz with no dependence on the presence or absence of subsurface hydrocarbons. Therefore, this method should not be used as a direct hydrocarbon indicator in these environments. Furthermore, the analyses provide no direct evidence to indicate that earthquakes are capable of stimulating the hydrocarbon reservoir in a way that could modify the spectral amplitude of the microtremor signal.