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P-mode Oscillations (p-mode + oscillation)
Selected AbstractsDynamics of oscillating relativistic tori around Kerr black holesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2005Olindo Zanotti ABSTRACT We present a comprehensive numerical study of the dynamics of relativistic axisymmetric accretion tori with a power-law distribution of specific angular momentum orbiting in the background space,time of a Kerr black hole. By combining general relativistic hydrodynamics simulations with a linear perturbative approach we investigate the main dynamical properties of these objects over a large parameter space. The astrophysical implications of our results extend and improve two interesting results that have been recently reported in the literature. First, the induced quasi-periodic variation of the mass quadrupole moment makes relativistic tori of nuclear matter densities, as those formed during the last stages of binary neutron star mergers, promising sources of gravitational radiation, potentially detectable by interferometric instruments. Secondly, p-mode oscillations in relativistic tori of low rest-mass densities could be used to explain high-frequency quasi-periodic oscillations observed in X-ray binaries containing a black hole candidate under conditions more generic than those considered so far. [source] The use of frequency-separation ratios for asteroseismologyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2005H. Otí Floranes ABSTRACT The systematic patterns of separations between frequencies of modes of different degree and order are a characteristic of p-mode oscillations of stars. The frequency separations depend on the internal structure of the star and so measuring them in the observed oscillation spectra of variable stars gives valuable diagnostics of the interior of a star. Roxburgh & Vorontsov proposed using the ratio of the so-called small frequency separation to the large frequency separation as a diagnostic of the stellar interior, and demonstrated that this ratio was less sensitive than the individual frequency separations themselves to uncertain details of the near-surface structure. Here we derive kernels relating the frequency separation ratio to structure, and show why the ratio is relatively insensitive to the near-surface structure in terms of the very small amplitude of the kernels in the near-surface layers. We also investigate the behaviour of the separation ratio for stars of different masses and ages, and demonstrate the usefulness of the ratio in the so-called asteroseismic Hertzsprung,Russell diagram. [source] Search for solar cycle changes in the signature of rapid variation in BiSON dataMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004G. A. Verner ABSTRACT The second helium ionization zone and the base of the convective envelope are regions of rapid variation of solar structure which introduce characteristic signatures into the frequencies of p-mode oscillations. These signals provide a direct seismological method to probe the acoustic properties of these regions. In this work we isolate these signatures in over 9 yr of low-degree BiSON data and extract information on the acoustic depth and local properties from each signal. Any temporal variations are investigated by fitting the signals extracted from 432, 864 and 1728-d spectra. The extracted parameters are found to be in agreement over the different length spectra and within one formal standard deviation of the values obtained for model ,S'. There is no evidence found for any systematic variation in the acoustic depth, width or magnitude of the second helium ionization zone, which suggests any activity-dependent disturbance to the near surface layers does not propagate down to this layer. The convection zone signal does show some temporal variation that may be correlated with solar activity, although further analysis with current data is required. The isolation of these signatures in low-degree data confirms that this method can be used to provide structural information on Sun-like stars once similar asteroseismic data become available. [source] Helioseismology program for the PICARD satellite,ASTRONOMISCHE NACHRICHTEN, Issue 5 2008T. Corbard Abstract The PICARD mission is a CNES micro-satellite to be launched in 2009. Its goal is to better understand the Sun and the potential impact of its activity on earth climate by measuring simultaneously the solar total and spectral irradiance, diameter, shape and oscillations. We present the scientific objectives, instrumental requirements and data products of the helioseismology program of PICARD which aims to observe the low to medium l p-mode oscillations in intensity and search for g-mode oscillation signatures at the limb. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||