On the emptiness of voids

The observability of a galaxy population inside of voids is estimated by assuming a void population similar to the one of nearby field galaxies in density as well as in morphological mixture. Obviously an extension to apparent magnitudes beyond m = 22 for a complete sample of galaxies in a sufficient large field is needed to get reliable information on a void population.     

POLE-TO-POLE SOLAR WIND DENSITY FROM ULYSSES RADIO MEASUREMENTS

We present new in situ measurements of solar wind electron density as a function of heliolatitude. The data were obtained on Ulysses during its fast transit from south solar pole to north solar pole, at heliocentric distance about 1.5 AU, near the 1996 solar activity minimum. The density is measured accurately using the method of quasi-thermal noise spectroscopy with the Ulysses radio experiment, at a higher time resolution than the particle analysers on board. At low heliolatitudes (22° S to 21° N) the histogram of our data shows three main classes of flows with densities centered at 3.5, 7, and 12 cm^-3, close to the values previously found by near-ecliptic space probes, in the region where fast coronal hole wind alternates with slower streamer belt wind. Poleward of 22° latitude where Ulysses encountered fast wind coming from coronal holes, the histogram of our data shows a single class of flow centered at 2.9 cm^-3 with a roughly normal distribution. We find a density nearly independent of latitude, with the mean density from the south coronal hole 10% larger than that from the north, which may stem from a genuine north/south asymmetry and/or from the small decrease in solar activity during the time of the observations. We finally compare the data with some analytical models.     

Exact Bianchi type-II, VIII and IX perfect fluid cosmological models in Saez-Ballester theory of gravitation

Exact Bianchi type-II, VIII and IX cosmological models are obtained in a scalar tensor theory proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) with perfect fluid as a source. Some physical and geometrical properties of the models are studied. It is observed that the models are free from initial singularities and they are expanding with time.     

Could CoRoT-7b and Kepler-10b be remnants of evaporated gas or ice giants?

We present thermal mass loss calculations over evolutionary time scales for the investigation if the smallest transiting rocky exoplanets CoRoT-7b (∼1.68R_Earth) and Kepler-10b (∼1.416R_Earth) could be remnants of an initially more massive hydrogen-rich gas giant or a hot Neptune-class exoplanet. We apply a thermal mass loss formula which yields results that are comparable to hydrodynamic loss models. Our approach considers the effect of the Roche lobe, realistic heating efficiencies and a radius scaling law derived from observations of hot Jupiters. We study the influence of the mean planetary density on the thermal mass loss by placing hypothetical exoplanets with the characteristics of Jupiter, Saturn, Neptune, and Uranus to the orbital location of CoRoT-7b at 0.017 AU and Kepler-10b at 0.01684 AU and assuming that these planets orbit a K- or G-type host star. Our findings indicate that hydrogen-rich gas giants within the mass domain of Saturn or Jupiter cannot thermally lose such an amount of mass that CoRoT-7b and Kepler-10b would result in a rocky residue. Moreover, our calculations show that the present time mass of both rocky exoplanets can be neither a result of evaporation of a hydrogen envelope of a “Hot Neptune” nor a “Hot Uranus”-class object. Depending on the initial density and mass, these planets most likely were always rocky planets which could lose a thin hydrogen envelope, but not cores of thermally evaporated initially much more massive and larger objects.     

The Maria asteroid family: Genetic relationships and a plausible source of mesosiderites near the 3:1 Kirkwood Gap

We present a mineralogical assessment of 12 Maria family asteroids, using near-infrared spectral data obtained over the years 2000-2009 combined with visible spectral data (when available) to cover the spectral interval of 0.4-2.5 μm. Our analysis indicates the Maria asteroid family, which is located adjacent to the chaotic region of the 3:1 Kirkwood Gap, appears to be a true genetic family composed of assemblages analogous to mesosiderite-type meteorites. Dynamical models by Farinella et al. (Farinella, P., Gunczi, R., Froeschlé, Ch., Froeschlé, C., [1993]. Icarus 101, 174-187) predict this region should supply meteoroids into Earth-crossing orbits. Thus, the Maria family is a plausible source of some or all of the mesosiderites in our meteorite collections. These individual asteroids were most likely once part of a larger parent object that was broken apart and dispersed. One of the Maria dynamical family members investigated, ((695) Bella), was found to be unrelated to the genetic Maria family members. The parameters of (695) Bella indicate an H-chondrite assemblage, and that Bella may be a sister or daughter of Asteroid (6) Hebe.     

The origin of our galactic magnetic field

A serious difficulty with the standard alpha‐omega theory of the origin of galactic magnetic fields involves the question of flux expulsion. This is intimately related to flux freezing. The alpha‐omega theory is shown in the context of the giant superbubble explosions that have a large impact on the physics of the interstellar medium. It is shown that superbubbles alone can duplicate the processes of the alpha‐omega dynamo and produce exponential growth of the galactic magnetic field. The possibility of the blow‐out of pieces of the magnetic field is discussed and it is shown that they have the potential to solve the flux‐expulsion problem. However, such an explanation must lead to apparent ‘gaps’ in the field in the galactic disc. These gaps are probably unavoidable in any dynamo theory and should have important observable consequences, one of which is an explanation for the escape of cosmic rays from the disc (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)