Active galactic nuclei heating in the centres of galaxy groups: a statistical study

We present gas temperature, density, entropy and cooling time profiles for the cores of a sample of 15 galaxy groups observed with Chandra . We find that the entropy profiles follow a power-law profile down to very small fractions of R ₅₀₀. Differences between the gas profiles of groups with radio-loud and radio-quiet brightest group galaxies are only marginally significant, and there is only a small difference in the   L _X: T _X  relations, for the central regions we study with Chandra , between the radio-loud and radio-quiet objects in our sample, in contrast to the much larger difference found on scales of the whole group in earlier work. However, there is evidence, from splitting the sample based on the mass of the central black holes, that repeated outbursts of active galactic nuclei (AGN) activity may have a long-term cumulative effect on the entropy profiles. We argue that, to first order, energy injection from radio sources does not change the global structure of the gas in the cores of groups, although it can displace gas on a local level. In most systems, it appears that AGN energy injection serves primarily to counter the effects of radiative cooling, rather than being responsible for the similarity breaking between groups and clusters.     

Vortical mechanism for generation of astrophysical jets

A vortical mechanism for generation of astrophysical jets is proposed based on exact solutions of the hydrodynamic equations with a generalized Rankine vortex. It is shown that the development of a Rankine vortex in the polar layer of a rotating gravitating body creates longitudinal fluxes of matter that converge toward the vortex trunk, providing an exponential growth in the angular rotation velocity of the trunk and a pressure drop on its axis. The increased rotational velocity of the vortex trunk and the on-axis pressure drop cease when the discontinuity in the azimuthal velocity at the surface of the trunk reaches the sound speed. During this time, ever deeper layers of the gravitating body are brought into the vortical motion, while the longitudinal velocity of the flow along the vortex trunk builds up, producing jet outflows of mass from its surface. The resulting vortices are essentially dissipationless. Dedicated to the 100-th birthday of Academician V. A. Ambartsumyan __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 201–218 (May 2008).     

Solar wind variation with the cycle

The cyclic evolution of the heliospheric plasma parameters is related to the time-dependent boundary conditions in the solar corona. “Minimal” coronal configurations correspond to the regular appearance of the tenuous, but hot and fast plasma streams from the large polar coronal holes. The denser, but cooler and slower solar wind is adjacent to coronal streamers. Irregular dynamic manifestations are present in the corona and the solar wind everywhere and always. They follow the solar activity cycle rather well. Because of this, the direct and indirect solar wind measurements demonstrate clear variations in space and time according to the minimal, intermediate and maximal conditions of the cycles. The average solar wind density, velocity and temperature measured at the Earth’s orbit show specific decadal variations and trends, which are of the order of the first tens per cent during the last three solar cycles. Statistical, spectral and correlation characteristics of the solar wind are reviewed with the emphasis on the cycles.     

Estimation of the Mode by the Dominant Cluster Method

A method is presented fop estimation of the mode of analytical data reported by cooperating analysts in the preparation of reference materials. The method is referred to as the dominant cluster method, and the nodal value obtained is the value that shows most agreement between analysts.
Several examples demonstrate that this mode (for which approximate confidence intervals have been estimated), is not inconsistent with the recommended values that have been assigned to well-known geochemical reference samples. Features in its favour are that the calculation is simple, it is independent of the type of distribution, and outliers are automatically excluded.     

The eSTAR network – agent architectures for astronomy

The eSTAR Project uses intelligent agent technologies to carry out resource discovery, submit observation requests and analyze the reduced data returned from a meta‐network of robotic telescopes. Linking ground based telescopes with astronomical satellites, and using the emerging field of intelligent agent architectures to provide crucial autonomous decision making in software, the project has succeeded in combining data archives and research class telescopes, along with distributed computing nodes, to build an ad‐hoc peer‐to‐peer heterogeneous network of resources. We present the current operations paradigm of the eSTAR network and describe the direction in which the project intends to develop over the next few years. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Speckle interferometric observations of Pluto and Charon

We report speckle interferometric observations of Pluto and its moon (1978 P1) Charon obtained on 5 June 1980 with a single 1.8-m mirror of the Multiple Mirror Telescope. Our observations yield a separation of 0″.31 (±0″.05) between Pluto and Charon at position angle 285° (±7°) for JD 2444395.75. This result and other direct observations indicate an adjustment of +4.0 hr to the orbital epoch of R. S. Harrington and J. W. Christy [Astron.J.86, 442–443 (1981)]. Our observation, which represents the first resolution of the system near minimum separation, also suggests that the inclination of the orbit to the plane of the sky should be increased by 3°; this will delay the onset of the predicted eclipsee season by one apparition to 1984 or 1985. Our data are consistent with Pluto diameter 0″.14 (±0″.02) = 3000 (±400) km and Charon diameter 0″..05 (±0″.03) = 1100 (±600) km.