Does an orbiting star cause periodic modulation of X-rays from NGC6814?
USING data from the Ginga satellite, Done et al.1 have confirmed an Exosat observation2 of high-amplitude periodic modulation in the X-ray emission from the Seyfert galaxy NGC6814. To within observational errors of ∼1%, the period seems to have remained constant at ∼12,100 seconds between 1985 and 1989. An obvious candidate for the phenomenon underlying the periodicity is the orbital motion of a star or low-mass compact object around the central black hole3. As we show here, the presence of an orbiting star could be verified easily by looking for the effects of Lense–Thirring precession of the orbital plane, caused by the dragging of inertia! frames around a rotating black hole. Precession-induced variations in the waveform and in the phase of the observed periodicity should have a period of between a month and a year. Such variations could account for the different waveforms present in the Ginga and Exosat data sets4, and may be detectable in existing Ginga and future Rosat, OSSE/GRO, and Astro-D data.
Neutrino-heated stars and broad-line emission from active galactic nuclei
Nonthermal radiation from active galactic nuclei indicates the presence of highly relativistic particles. The interaction of these high-energy particles with matter and photons gives rise to a flux of high-energy neutrinos. In this paper, the influence of the expected high neutrino fluxes on the structure and evolution of single, main-sequence stars is investigated. Sequences of models of neutrino-heated stars in thermal equilibrium are presented for masses 0.25, 0.5, 0.8, and 1.0 solar mass. In addition, a set of evolutionary sequences for mass 0.5 solar mass have been computed for different assumed values for the incident neutrino energy flux. It is found that winds driven by the heating due to high-energy particles and hard electromagnetic radiation of the outer layers of neutrino-bloated stars may satisfy the requirements of the model of Kazanas (1989) for the broad-line emission clouds in active galactic nuclei.
Effect of antioxidants, on deterioration by partial discharge in LDPE and XLPE [insulation materials]
The effect of antioxidants in low-density polyethylene (LDPE) and cross-linked polyethylene (XLPE) on deterioration by partial discharge (PD) was investigated. Experiments were conducted using LDPE and XLPE samples containing phenolic antioxidants. Samples subjected to the PD were analyzed using atomic force microscopy and Fourier transform infrared analysis (AFM and FTIR). AFM images demonstrated that the magnitude of pits created in the sample containing antioxidants was smaller than that in samples containing no antioxidant. FTIR showed that oxidative degradation occurred on LDPE and XLPE surfaces when they were subjected to PD. These results confirmed that the amount of oxidized substances was smaller in samples containing phenolic antioxidants than in those containing no antioxidant. This report elucidates the mechanism of antioxidant action on deterioration by PD.