Numerical simulations are a crucial tool to understand the relationship between debris discs and planetary companions. As debris disc observations are now reaching unprecedented levels of precision over a wide range of wavelengths, an appropriate level of accuracy and consistency is required in numerical simulations to confidently interpret this new generation of observations. However, simulations throughout the literature have been conducted with various initial conditions often with little or no justification. In this paper, we aim to study the dependence on the initial conditions of N-body simulations modelling the interaction between a massive and eccentric planet on an exterior debris disc. To achieve this, we first classify three broad approaches used in the literature and provide some physical context for when each category should be used. We then run a series of N-body simulations, that include radiation forces acting on small grains, with varying initial conditions across the three categories. We test the influence of the initial parent body belt width, eccentricity, and alignment with the planet on the resulting debris disc structure and compare the final peak emission location, disc width and offset of synthetic disc images produced with a radiative transfer code. We also track the evolution of the forced eccentricity of the dust grains induced by the planet, as well as resonance dust trapping. We find that an initially broad parent body belt always results in a broader debris disc than an initially narrow parent body belt. While simulations with a parent body belt with low initial eccentricity (e ~ 0) and high initial eccentricity (0 < e < 0.3) resulted in similar broad discs, we find that purely secular forced initial conditions, where the initial disc eccentricity is set to the forced value and the disc is aligned with the planet, always result in a narrower disc. We conclude that broad debris discs can be modelled by using either a dynamically cold or dynamically warm parent belt, while in contrast eccentric narrow debris rings are reproduced using a secularly forced parent body belt.

Analyses of QSO absorption lines show that the HI content has evolved over the redshift range z = 5 to z = 0. The 21-cm line measurements of the z = 0 HI content avoid several biases inherent in the absorption-line technique, such as the influence of evolving dust content in the absorbers, and will produce a reliable measure to anchor theories of galaxy evolution. Examples of important questions to be addressed by local HI surveys are: (1) Is there a significant population of gas-rich galaxies or intergalactic clouds that is missing from the census of optically selected galaxies? (2) Is there an adequate reservoir of neutral gas to substantially prolong star formation at its present rate? (3) Are there massive objects of such low HI column density that they can have escaped detection in the ‘unbiased’ HI surveys that have been conducted so far?

Models of average Galactic chemical abundances are in good general agreement with observations for [Fe/H] > –1.5, but there are gross discrepancies at lower metallicities. Only massive stars contribute to the chemical evolution of the ‘juvenile universe’ corresponding to [Fe/H] ≲ –1.5. If Type II supernovae (SNe II) are the only relevant sources, then the abundances in the interstellar medium of the juvenile epoch are simply the sum of different SN II contributions. Both low-mass (∼8–11 M⊙) and normal (∼12–25 M⊙) SNe II produce neutron stars, which have intense neutrino-driven winds in their nascent stages. These winds produce elements such as Sr, Y and Zr through charged-particle reactions (CPR). Such elements are often called the ‘light r-process elements’, but are considered here as products of CPR and not the r process. The observed absence of production of the low-A elements (Na through Zn including Fe) when the true r-process elements (Ba and above) are produced requires that only low-mass SNe II be the site if the r process occurs in SNe II. Normal SNe II produce the CPR elements in addition to the low-A elements. This results in a two-component model that is quantitatively successful in explaining the abundances of all elements relative to hydrogen for –3 ≲ [Fe/H] ≲ –1.5. This model explicitly predicts that [Sr/Fe] ≥ –0.32. Recent observations show that there are stars with [Sr/Fe] ≲ –2 and [Fe/H] < –3. This proves that the two-component model is not correct and that a third component is necessary to explain the observations. The production of CPR elements associated with the formation of neutron stars requires that the third component must be massive stars ending as black holes. It is concluded that stars of ∼25–50 M⊙ (possibly up to ∼100 M⊙) are the appropriate candidates. These produce hypernovae (HNe) that have very high Fe yields and are observed today. Stars of ∼140–260 M⊙ are completely disrupted upon explosion. However, they produce an abundance pattern greatly deficient in elements of odd atomic numbers, which is not observed, and therefore they are not considered as a source here. Using a Salpeter initial mass function, it is shown that HNe are a source of Fe that far outweighs normal SNe II, with the former and the latter contributing ∼24% and ∼9% of the solar Fe abundance, respectively. It follows that the usual assignment of ∼⅓ of the solar Fe abundance to normal SNe II is not correct. This leads to a simple three-component model including low-mass and normal SNe II and HNe, which gives a good description of essentially all the data for stars with [Fe/H] ≲ –1.5. We conclude that HNe are more important than normal SNe II in the chemical evolution of the low-A elements from Na through Zn (including Fe), in sharp distinction to earlier models.

The 2dF Galaxy Redshift Survey (2dFGRS) of 230 000 redshifts of nearby (z ~ 0.1) galaxies is now complete. It has allowed the 2dFGRS Team and others to estimate fundamental cosmological parameters and to study galaxy intrinsic properties. Here we highlight three recent key results from the survey: (a) an upper limit of about 2 eV on the total mass of the three neutrino flavours, and an intriguing reasonable fitting of the 2dFGRS power spectrum to a Mixed Dark Matter model without a Cosmological Constant but with a low Hubble constant; (b) the bimodality of the galaxy population in both spectral parameterisation and in colour; and (c) the clustering of different galaxy types and evidence for relative stochastic biasing.

With the discovery of now more than 500 exoplanets, we present a statistical analysis of the planetary orbital periods and their relationship to the rotation periods of their parent stars. We test whether the structural variables of planetary orbits, i.e. planetary angular momentum and orbital period, are ‘quantized’ in integer or half-integer multiples of the parent star's rotation period. The Solar System is first shown to exhibit quantized planetary orbits that correlate with the Sun's rotation period. The analysis is then expanded over 443 exoplanets to statistically validate this quantization and its association with stellar rotation. The results imply that the exoplanetary orbital periods are highly correlated with the parent star's rotation periods and follow a discrete half-integer relationship with orbital ranks n = 0.5, 1.0, 1.5, 2.0, 2.5, etc. The probability of obtaining these results by pure chance is p < 0.024. We discuss various mechanisms that could justify this planetary quantization, such as the hybrid gravitational instability models of planet formation, along with possible physical mechanisms such as the inner disc's magnetospheric truncation, tidal dissipation, and resonance trapping. In conclusion, we statistically demonstrate that a quantized orbital structure should emerge from the formation processes of planetary systems and that this orbital quantization is highly dependent on the parent star's rotation period.

In this brief communication, a new method is outlined for modelling magnification patterns on an observer’s plane using a first-order approximation to the null geodesic path equations for a point mass lens. For each ray emitted from a source, an explicit calculation is made for the change in position on the observer’s plane due to each lens mass. By counting the number of points in each small area of the observer’s plane, the magnification at that point can be determined. This allows for a very simple and transparent algorithm. A short Matlab code sample for creating simple magnification maps due to multiple point lenses is included in an appendix.

We present near-infrared images and spectra of the peculiar radio galaxy Centaurus A. The images reveal extended emission regions at the longer wavelengths and show colours characteristic of reddened starlight. We believe we are seeing stars within the warped disc of Cen A, which are obscured in the optical by dust. Both images and spectra indicate the presence of a compact core, whose colours are much redder than those of the surrounding stars. In the spectrum of the core, detections have been made of [Fe II] 1.644 μm, H2 2.122 μm and Br γ. These lines appear to peak on the nucleus and their presence and width suggest starburst activity.

This paper discusses the boundary layer and the emission spectrum from an accretion disk having a jet anchored at its inner radius, close to the black hole. We summarise our earlier work and apply it to the accretion disks of some blazars. We suggest that the ‘accretion disk with jet’ (ADJ) model could make the bridge between standard accretion disk models (suitable for quasars and FRii sources) and low-power advection dominated accretion disk models (suitable for some of the low-power BL Lacs and FRi sources).

The jet is collimated within a very narrow region close to the black hole (nozzle). In our model it is assumed that the boundary layer of the disk is the region between radius Rms — the last marginally stable circular orbit calculated for a Kerr geometry — and the radius Rjet, which gives the thickness of the ‘footring’, i.e. the base of the jet. We analyse the size of the boundary layer of the disk where the jet is fed with energy, mass, and angular momentum. As a consequence of the angular momentum extraction, the accretion disk beyond Rjet no longer has a Keplerian flow. A hot corona usually surrounds the disk, and entrainment of the corona along the flow could also be important for the energy and mass budget of the jet.

We assume that the gravitational energy available at the footring of the jet goes into the jet, and so the spectrum from the accretion disk gives a total luminosity smaller than that of a ‘standard’ accretion disk, and our ADJ model should apply for blazars with low central luminosities. Variations of the boundary layer and nozzle may account for some of the variability observed in active galactic nuclei.

One of the most difficult tasks facing theoretical astrophysics today is to find a satisfactory model for the convective transport of energy in regions where the temperature gradient is superadiabatic. A number of such models have been proposed, such as the mixing-length theory and its extensions (Vitense 1953, Böhm-Vitense 1958, Spiegel 1963, Travis and Matsushima 1973 a, b, Parson 1969), to take into account the combined effects of convection and turbulence but it is generally agreed that, to-date, no satisfactory theory has been put forward.

EX Hya was one of the earliest detected eclipsing cataclysmic variables. The 98 min orbital period was first documented as a result of the spectroscopy of Kraft and Krzeminski (1962) and the photometry of Mumford (1964, 1967). However, new properties of this system continue to be discovered and these have required a more complex model than was previously envisaged.

The energy dissipated by virialisation shocks during hierarchical structure formation of the Galaxy can exceed that injected by concomitant supernova (SN) explosions. Cosmic rays (CRs) accelerated by such shocks may therefore dominate over SNe in the production of 6Li through α + α fusion without co-producing Be and B. This process can give a more natural account of the observed 6Li abundance in metal-poor stars compared to standard SN CR scenarios. Future searches for correlations between the 6Li abundance and the kinematic properties of halo stars may constitute an important probe of how the Galaxy and its halo formed. Furthermore, 6Li may offer interesting clues to some fundamental but currently unresolved issues in cosmology and structure formation on sub-galactic scales.

In this paper we present maps showing the distribution of HCO+ (J= 1→0 transition at 89.18855 GHz) in the direction of NGC 6334 as a function of radial velocity, lhe observations were carried out in May-June 1979 as part of a larger program of HCO+ observations (Batchelor et al. 1980, 1981) using the Epping 4-m millimetre-wave radio telescope.

Many cold molecular clouds have been detected as a result of their association with dense optical obscuration. The HII region RCW 36 is contained within a prominent dust lane extending several degrees along a line of almost constant right ascension (see e.g. Rodgers et al. 1960). By means of H2CO and OH observations we have found that this lane is associated with a dense elongated molecular cloud.

In the wide complex profiles of OH, H2CO and CO spectra observed in directions towards the galactic centre, only the features at radial velocities near + 40 km s-1 are generally believed to originate in the molecular clouds nearest the galactic nucleus. The features at other velocities are associated with clouds or spiral features that can be traced over larger ranges of galactic longitude, implying locations which are more distant from the nucleus. In particular, the features near zero velocity have been traditionally associated with molecular clouds within 1-2 kpc of the Sun. However, H2CO observations with high velocity resolution provide evidence that one cloud with velocity near zero is probably near the galactic nucleus.

The purpose of this paper is to advance an alternative hypothesis for the underlying distinction between solar radio bursts of spectral type V and ‘inverted U’ bursts, and to explore its implications.

We present a new determination of the solar nitrogen abundance making use of 3D hydrodynamical modelling of the solar photosphere, which is more physically motivated than traditional static 1D models. We selected suitable atomic spectral lines, relying on equivalent width measurements already existing in the literature. For atmospheric modelling we used the co5bold 3D radiation hydrodynamics code. We investigated the influence of both deviations from local thermodynamic equilibrium (non-LTE effects) and photospheric inhomogeneities (granulation effects) on the resulting abundance. We also compared several atlases of solar flux and centre-disc intensity presently available. As a result of our analysis, the photospheric solar nitrogen abundance is A(N) = 7.86 ± 0.12.

The aggregation of a large number of planetesimals into a single body is a problem that has proved to be a stumbling block for many theories of planetary formation. This difficulty has mainly arisen because of the tendency of an orbiting stream of bodies to disperse over the equatorial plane as a result of the combined effects of collisions and gravitational interactions (Trulsen 1972; Brahic 1975). Once such a chaotic distribution of orbiting bodies has developed, it is extremely difficult for these bodies to subsequently accumulate into a single entity. This problem does not arise, however, when aggregation takes place within a differentially rotating gaseous ring as proposed by Prentice (1978). It has been shown previously (Hourigan 1977) that the gas drag overcomes the disruptive nature of collisional interactions, resulting in the formation of a thin concentrated torus of orbiting bodies.

To investigate the ultraviolet (UV) activity of the bright, non-eclipsing, double-lined spectroscopic binary system UX Ari, IUE spectra (194 images) were taken from the IUE archive. The spectra, obtained during the period 1978–1996, show emission lines originating in the chromosphere and transition region. The long-wavelength low dispersion spectra were examined for ultraviolet excess by comparing the UV continuum level of UX Ari with the levels of k Cet and η Cep in the spectral range 2100–3200 Å. The individual Mgiih and k emission-line fluxes of component stars show that the contributions to the activity of the system for G5 V and K0 IV are about 20% and 80%, respectively. Apart from the flare event observed on 1979 Jan 1, there are some flux enhancements in the years 1987, 1991 and 1994 which may suggest existence of a periodicity of about 7–9 years. Examination of the ultraviolet excess in the system showed that there is some UV excess in UX Ari, which varies from 1% up to 24% with the exception of two images which showed no UV excess. The results revealed that there was an agreement on the source of emission regions which could be attributed to magnetic activity. The contribution of G5 V and K0 IV components to the Mgii activity of the system suggests a need to take into consideration the spot distribution not only on the surface of the K0 IV but also on the surface of the G5 V component of UX Ari.

The Figaro data reduction system was originally written for DEC VAXes running VMS, and little attention was paid to making it portable. Recently, however, a cooperative effort between the AAO, MSSSO, UNSW, the UK Starlink network and Caltech has resulted in a version for UNIX. This new version has been run under VMS and three different versions of UNIX. The files produced by any version may be read directly by any other version, although Figaro has a particularly complex file format which contains an extensible, self-defining, hierarchical structure of data items. This complexity has allowed the addition of error and quality data, as well as specific structures used, for example, for echelle data. Figaro is written mainly in Fortran (with numerous DEC extensions) but there is also a significant use of C. While C and Fortran are reasonably portable, the way one is called from the other is less portable and needs careful handling. Ports to other systems are possible, with effort; a Macintosh version is being considered.

Pulsars have been studied extensively over the last few decades and have proven instrumental in exploring a wide variety of physics. Discovering more pulsars emitting at low radio frequencies is crucial to further our understanding of spectral properties and emission mechanisms. The Murchison Widefield Array Voltage Capture System (MWA VCS) has been routinely used to study pulsars at low frequencies and discover new pulsars. The MWA VCS offers the unique opportunity of recording complex voltages from all individual antennas (tiles), which can be off-line beamformed or correlated/imaged at millisecond time resolution. Devising imaged-based methods for finding pulsar candidates, which can be verified in beamformed data, can accelerate the complete process and lead to more pulsar detections. Image-based searches for pulsar candidates can reduce the number of tied-array beams required, increasing compute resource efficiency. Despite a factor of $\sim$4 loss in sensitivity, searching for pulsar candidates in images from the MWA VCS, we can explore a larger parameter space, potentially leading to discoveries of pulsars missed by high-frequency surveys such as steep spectrum pulsars, exotic binary systems, or pulsars obscured in high-time resolution time series data by propagation effects. Image-based searches are also essential to probing parts of parameter space inaccessible to traditional beamformed searches with the MWA (e.g. at high dispersion measures). In this paper we describe the innovative approach and capability of dual-processing MWA VCS data, that is forming 1-s visibilities and sky images, finding pulsar candidates in these images, and verifying by forming tied-array beam. We developed and tested image-based methods of finding pulsar candidates, which are based on pulsar properties such as steep spectral index, polarisation and variability. The efficiency of these methodologies has been verified on known pulsars, and the main limitations explained in terms of sensitivity and low-frequency spectral turnover of some pulsars. No candidates were confirmed to be a new pulsar, but this new capability will now be applied to a larger subset of observations to accelerate pulsar discoveries with the MWA and potentially speed up future searches with the SKA-Low.