On the energy integral for first post-Newtonian approximation

The post-Newtonian approximation for general relativity is widely adopted by the geodesy and astronomy communities. It has been successfully exploited for the inclusion of relativistic effects in practically all geodetic applications and techniques such as satellite/lunar laser ranging and very long baseline interferometry. Presently, the levels of accuracy required in geodetic techniques require that reference frames, planetary and satellite orbits and signal propagation be treated within the post-Newtonian regime. For arbitrary scalar W and vector gravitational potentials \(W^j (j=1,2,3)\), we present a novel derivation of the energy associated with a test particle in the post-Newtonian regime. The integral so obtained appears not to have been given previously in the literature and is deduced through algebraic manipulation on seeking a Jacobi-like integral associated with the standard post-Newtonian equations of motion. The new integral is independently verified through a variational formulation using the post-Newtonian metric components and is subsequently verified by numerical integration of the post-Newtonian equations of motion.     

Merger histories in warm dark matter structure formation scenarios

Observations on galactic scales seem to be in contradiction with recent high-resolution N -body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy haloes. In this paper, we explore a different approach that consists of filtering the dark matter power spectrum on small scales, thereby altering the formation history of low-mass objects. The physical motivation for damping these fluctuations lies in the possibility that the dark matter particles have a different nature, i.e. are warm (WDM) rather than cold. We show that this leads to some interesting new results in terms of the merger history and large-scale distribution of low-mass haloes, compared with the standard CDM scenario. However, WDM does not appear to be the ultimate solution, in the sense that it is not able to fully solve the CDM crisis, even though one of the main drawbacks, namely the abundance of satellites, can be remedied. Indeed, the cuspiness of the halo profiles still persists, at all redshifts, and for all haloes and sub-haloes that we investigated. Despite the persistence of the cuspiness problem of DM haloes, WDM seems to be still worth taking seriously, as it alleviates the problems of over-abundant sub-structures in galactic haloes and possibly the lack of angular momentum of simulated disc galaxies. WDM also lessens the need to invoke strong feedback to solve these problems, and may provide a natural explanation of the clustering properties and ages of dwarfs.     

Meteoric Be in soil profiles - A global meta-analysis

In order to assess current understanding of meteoric ¹⁰Be dynamics and distribution in terrestrial soils, we assembled a database of all published meteoric ¹⁰Be soil depth profiles, including 104 profiles from 27 studies in globally diverse locations, collectively containing 679 individual measurements. This allows for the systematic comparison of meteoric ¹⁰Be concentration to other soil characteristics and the comparison of profile depth distributions between geologic settings. Percent clay, ⁹Be, and dithionite-citrate extracted Al positively correlate to meteoric ¹⁰Be in more than half of the soils where they were measured, but the lack of significant correlation in other soils suggests that no one soil factor controls meteoric ¹⁰Be distribution with depth. Dithionite-citrate extracted Fe and cation exchange capacity are only weakly correlated to meteoric ¹⁰Be. Percent organic carbon and pH are not significantly related to meteoric ¹⁰Be concentration when all data are complied.The compilation shows that meteoric ¹⁰Be concentration is seldom uniform with depth in a soil profile. In young or rapidly eroding soils, maximum meteoric ¹⁰Be concentrations are typically found in the uppermost 20 cm. In older, more slowly eroding soils, the highest meteoric ¹⁰Be concentrations are found at depth, usually between 50 and 200 cm. We find that the highest measured meteoric ¹⁰Be concentration in a soil profile is an important metric, as both the value and the depth of the maximum meteoric ¹⁰Be concentration correlate with the total measured meteoric ¹⁰Be inventory of the soil profile.In order to refine the use of meteoric ¹⁰Be as an estimator of soil erosion rate, we compare near-surface meteoric ¹⁰Be concentrations to total meteoric ¹⁰Be soil inventories. These trends are used to calibrate models of meteoric ¹⁰Be loss by soil erosion. Erosion rates calculated using this method vary based on the assumed depth and timing of erosional events and on the reference data selected.     

Consequences of the tidal slowing of Mercury

Mercury, currently rotating very slowly, probably rotated faster in the past. If Mercury's rotation period had been near 8 hours initially, similar to that of most solar system bodies today, it would have been flattened by a few percent. As Mercury was slowed by solar tides, craters which were circular when they were emplaced would have been distorted by the same few percent. Substantial surface stresses, well above the fracture stress, would have been produced unless stress relief occurred; these stresses should have produced tensional fractures near the poles and two intersecting sets of shear planes in equatorial regions. Satellite orbits about the slowly spinning Mercury have been shown to collapse onto its surface: the impact craters resulting from these hypothetical lost satellites should be elongated along the orbit paths, which probably lie near the equator. However, none of these features has been found on the Mariner 10 images. They may be obscured by the effects of tidal heating that should cause an overall internal temperature increase of about 100°K although the increase would be substantially more in certain regions. Radial tides, sometimes called push-pull tides, are important at the present time because Mercury's large orbital eccentricity causes the planet to undergo significant tidal flexing each orbital period; the contemporary tidal heating due to this mechanism is estimated at more than 10¹⁶ erg/sec.     

Spectral photometry of selected areas of the lunar surface during maximum solar activity

Photoelectric observations have been carried out during maximum solar activity in order to investigate the variation of the brightness of the lunar surface with the solar cycle and to detect the possiblity of existing colour anomaly. The brightness data, using a wide-passband filter, do not show any evidence of variation with the solar cycle. No colour anomaly is found for the investigated lunar regions, and the doubt that has been felt by some investigators about the nonexistence of certain colour indices' variation with phase is not confirmed.     

Electron Temperatures and Flow Speeds of the Low Solar Corona: MACS Results from the Total Solar Eclipse of 29 March 2006 in Libya

An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the measured K-coronal spectra to interpret the observations. Results show electron temperatures of (1.10±0.05) MK, (0.70±0.08) MK, and (0.98±0.12) MK, at 1.1 R _⊙ from Sun center in the solar north, east and west, respectively, and (0.93±0.12) MK, at 1.2 R _⊙ from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103±92) km s⁻¹, (0+10) km s⁻¹, (0+10) km s⁻¹, and (0+10) km s⁻¹. Since the observations were taken only at 1.1 R _⊙ and 1.2 R _⊙ from Sun center, these speeds, consistent with zero outflow, are in agreement with expectations and provide additional confirmation that the spectral fitting method is working. The electron temperature at 1.1 R _⊙ from Sun center is larger at the north (polar region) than the east and west (equatorial region).     

Observational Evidence for a Double-Helix Structure in CMEs and Magnetic Clouds

We compare recent observations of a solar eruptive prominence as seen in extreme-UV light on 30 March 2010 by the Solar Dynamics Observatory (SDO) with the multi-tube model for interplanetary magnetic clouds (Osherovich, Fainberg, Stone, Geophys. Res. Lett. 26, 2597, 1999). Our model is based on an exact analytical solution of the plasma equilibrium with magnetic force balanced by a gradient of scalar gas pressure. Topologically, this solution describes two magnetic helices with opposite magnetic polarity embedded in a cylindrical magnetic flux tube that creates magnetic flux inequality between the two helices by enhancing one helix and suppressing the other. The magnetic field in this model is continuous everywhere and has a finite magnetic energy per unit length of the tube. These configurations have been introduced as MHD bounded states (Osherovich, Soln. Dannye 5, 70, 1975). Apparently, the SDO observations depict two non-equal magnetically interacting helices described by this analytical model. We consider magnetic and thermodynamic signatures of multiple magnetic flux ropes inside the same magnetic cloud, using in situ observations. The ratio of magnetic energy density to bulk speed solar wind energy density has been defined as a solar wind quasi-invariant (QI). We analyze the structure of the QI profile to probe the topology of the internal structure of magnetic clouds. From the superposition of 12 magnetically isolated clouds observed by Ulysses, we have found that the corresponding QI is consistent with our double helix model.     

Reionization and the Cosmic Dawn with the Square Kilometre Array

The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.