Very Large Array observations of broad 6-cm excited-state OH lines in W49A

Using the Very Large Array (VLA), we observed all three of the 6-cm lines of the  ²Π_1/2, J = 1/2  state of OH with sub-arcsecond resolution (∼0.4 arcsec) in W49A. While the spatial distribution and the range in velocities of the 6-cm lines are similar to those of the ground-state (18-cm) OH lines, a large fraction of the total emission in all three 6-cm lines has large linewidths (∼5–10 km s⁻¹) and is spatially extended, very unlike typical ground-state OH masers, which typically are point-like at VLA resolutions and have linewidths ≤1 km s⁻¹. We find brightness temperatures of 5900, 4700 and ≥730 K for the 4660, 4750 and 4765-MHz lines, respectively. We conclude that these are indeed maser lines. However, the gains are ∼0.3, again very unlike the 18-cm lines, which have gains  ≥10⁴  . We compare the excited-state OH emission with that from other molecules observed with comparable angular resolution to estimate physical conditions in the regions emitting the peculiar, low-gain maser lines. We also comment on the relationship with the 18-cm masers.     

Collapsing supra-massive magnetars: FRBs,the repeating FRB121102 and GRBs

Fast Radio Bursts (FRBs) last for \(\sim \) few milli-seconds and, hence, are likely to arise from the gravitational collapse of supra-massive, spinning neutron stars after they lose the centrifugal support (Falcke & Rezzolla 2014). In this paper, we provide arguments to show that the repeating burst, FRB 121102, can also be modeled in the collapse framework provided the supra-massive object implodes either into a Kerr black hole surrounded by highly magnetized plasma or into a strange quark star. Since the estimated rates of FRBs and SN Ib/c are comparable, we put forward a common progenitor scenario for FRBs and long GRBs in which only those compact remnants entail prompt \(\gamma \)-emission whose kick velocities are almost aligned or anti-aligned with the stellar spin axes. In such a scenario, emission of detectable gravitational radiation and, possibly, of neutrinos are expected to occur during the SN Ib/c explosion as well as, later, at the time of magnetar implosion.     

The Maltese Islands: climate, vegetation and landscape

The Maltese Islands, situated in the central Mediterranean, occupy an area of only some 316 km². The climate is typically Mediterranean: the average annual rainfall is c. 530 mm of which some 85% falls during the period October to March; the mean monthly temperature range is 12--26 °C, and the islands are very windy and sunny. Although small, the Maltese Islands have a considerable diversity of landscapes and ecosystems which are representative of the range and variety of those of the Mediterranean region. The islands are composed mainly of limestones, the soils are young and are very similar to the parent rocks, and there are no mountains, streams or lakes, but only minor springs; the main geomorphological features are karstic limestone plateaux, hillsides covered with clay taluses, gently rolling limestone plains, valleys which drain runoff during the wet season, steep sea-cliffs on the south-western coasts, and gently sloping rocky shores to the Northeast. The main vegetational assemblages are maquis, garigue and steppe; minor ones include patches of woodland, coastal wetlands, sand dunes, freshwater, and rupestral communities; the latter are the most scientifically important in view of the large number of endemic species they support. Human impact is significant. Some 38% of the land area is cultivated, c. 15% is built up, and the rest is countryside. The present landscape is a result of the interaction of geology and climate, coupled with the intense human exploitation of the environment over many thousands of years, which has altered the original condition of the vegetation cover, principally through the diversion of vast tracts of land to cultivation, the construction of terraces, water catchment devices, irrigation channels and drainage ditches, the grazing of animals on uncultivated land, and the development of land for buildings and industry. The scantiness of the soil, combined with the erratic rainfall and the periodic disturbance of the vegetation cover, has resulted in extensive erosion. As a consequence it is now difficult for the original vegetation to reassert itself, affecting the landscape drastically and permanently. Much of the original native flora has been lost or marginalised and the present day non-urban landscape is now dominated by vegetation consisting mainly of ruderal and introduced species. As the population increases, and human pressure on the environment mounts, such trends are likely to continue and it is only very recently that some important initiatives have been taken to manage the environment and halt the deterioration of the landscape.     

Exoplanet atmospheres with EChO: spectral retrievals using EChOSim

We demonstrate the effectiveness of the Exoplanet Characterisation Observatory mission concept for constraining the atmospheric properties of hot and warm gas giants and super Earths. Synthetic primary and secondary transit spectra for a range of planets are passed through EChOSim [13] to obtain the expected level of noise for different observational scenarios; these are then used as inputs for the NEMESIS atmospheric retrieval code and the retrieved atmospheric properties (temperature structure, composition and cloud properties) compared with the known input values, following the method of [1]. To correctly retrieve the temperature structure and composition of the atmosphere to within 2 σ, we find that we require: a single transit or eclipse of a hot Jupiter orbiting a sun-like (G2) star at 35 pc to constrain the terminator and dayside atmospheres; 20 transits or eclipses of a warm Jupiter orbiting a similar star; 10 transits/eclipses of a hot Neptune orbiting an M dwarf at 6 pc; and 30 transits or eclipses of a GJ1214b-like planet.     

Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables – II. A low-inertia magnetic accretor model

The dwarf nova oscillations observed in cataclysmic variable (CV) stars are interpreted in the context of a low-inertia accretor model, in which accretion on to an equatorial belt of the white dwarf primary causes the belt to vary its angular velocity. The rapid deceleration phase is attributed to propellering. Evidence that temporary expulsion rather than accretion of gas occurs during this phase is obtained from the large drop in extreme ultraviolet flux.
We show that the quasi-periodic oscillations are most probably caused by a vertical thickening of the disc, moving as a travelling wave near the inner edge of the disc. This alternately obscures and 'reflects' radiation from the central source, and is visible even in quite low inclination systems. A possible excitation mechanism, caused by winding up and reconnection of magnetic field lines, is proposed.
We apply the model, deduced largely from VW Hyi observations, to re-interpret observations of SS Cyg, OY Car, UX UMa, V2051 Oph, V436 Cen and WZ Sge. In the last of these we demonstrate the existence of a 742-s period in the light curve, arising from obscuration by the travelling wave, and hence show that the two principal oscillations are a dwarf nova oscillation and its reprocessed companion.     

Oort Cloud Comet Perihelion Asymmetries: Galactic Tide, Shower or Observational Bias?

We investigate the distribution of Oort cloud comet perihelia. The data considered includes comets having orbital elements of the two highest quality classes with original energies designated as new or young. Perihelion directions are determined in galactic, ecliptic and geocentric equatorial coordinates. Asymmetries are detected in the scatter and are studied statistically for evidence of adiabatic galactic tidal dynamics, an impulse-induced shower and observational bias. The only bias detected is the well-known deficiency of observations with perihelion distances q > 2.5 AU. There is no significant evidence of a seasonal dependence. Nor is there a substantive hemispherical bias in either ecliptic or equatorial coordinates. There is evidence for a weak stellar shower previously detected by Biermann which accounts for ≈ 10% of the total observations. Both the q bias and the Biermann star track serve to weaken the evidence for a galactic tidal imprint. Nevertheless, statistically significant asymmetries in galactic latitude and longitude of perihelia remain. A latitude asymmetry is produced by a dominant tidal component perpendicular to the galactic disk. The longitude signal implies that ≈ 20% of new comets need an additional dynamical mechanism. Known disk non-uniformities and an hypothetical bound perturber are discussed as potential explanations. We conclude that the detected dynamical signature of the galactic tide is real and is not an artifact of observational bias, impulsive showers or poor data. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the cooling of the moon by solid convection

If a molten, or partially molten, lunar core exists at present, constraints would be placed on the viscosity of the solid mantle and the distribution of radioactive heat sources. Models in which the heat sources have been concentrated near the surface would rapidly solidify if the effective viscosity was equal to, or less than, 10²² cm² s⁻¹. Retention of most of the heat sources throughout the mantle would permit present day solid convection to occur without cooling the core.     

Influence of cluster environments on X-ray cluster morphology

We investigated the influence of environment on cluster morphology by examining the alignment of the cluster position angle with respect to the nearest neighbour cluster. The cluster position angle and ellipticity were measured using high spatial resolution X-ray data taken from the Chandra archive, while the nearest neighbour sample was extracted from the Abell cluster catalogue. We found high confidence for an alignment when neighbour distance (Dn) was less than  70  h ⁻¹  Mpc, while we found no significant variations of the confidence level at various values of Dn less than  70  h ⁻¹  Mpc.     

Characterisation of Soot Emitted by Domestic Heating,Aircraft and Cars Using Diesel or Biodiesel

The characterisation of aggregates, like soot, firstly requires the determination of the size distribution of the primary particles. The primary particle size of combustion generated aggregates depends upon the combustion environment and the formation conditions, such as temperature, pressure and fuel-to-air ratio, among others. Since the combustion characteristics are different in the different types of burners, the characterisation of primary particles may offer the possibility to distinguish soot from different sources. In this paper, we present the signature of the primary particles and the aggregates of soot emitted by cars using diesel or biodiesel, by domestic heating, and by aircraft exhausts, which can be considered as the major sources as derived from measurements on transmission electron micrographs. The size distributions of all aggregates types with different aerodynamic diameter were log-normal and quasi-monodisperse. The size distribution of the primary particles for soot emitted by different sources showed minor differences. However, a comparison between the diameter of the primary particles and those obtained using a standard method for carbon black revealed discrepancies. The median diameter of the primary particles was combined with the median number of primary particles in an aggregate to calculate the relative particle surface area available for adsorption. In a similar way, the relative specific surface area was determined. The surface area was measured using the Brunauer-Emmett-Teller (B.E.T.) nitrogen adsorption method and the relative surface area available for adsorption was calculated.