Conveners
APSS
- Christian Engelbrecht (University of Johannesburg)
APSS
- Christo Venter (North-west University, Potchefstroom Campus)
APSS
- Derck Smits (University of SA)
APSS
- Claude Carignan (University of Cape Town)
APSS
- Phil Charles (SAAO)
APSS
- Andrew Collier (Hermanus Magnetic Observatory)
APSS
- Shimul Kumar Maharaj (Hermanus Magnetic Observatory)
Description
Astrophysics and Space Science
Following the repair of the SALT optics in late 2010, the telescope has reentered the commissioning phase with its principal scientific instruments, SALTICAM and RSS. Both these instruments have undergone major refurbishments in their own right, and their current status and that of the telescope will be described, together with an update on its performance.
The advent of international wideband communication by optical fibre has produced a revolution in communications and the use of the internet. Many African countries are now connected to undersea fibre linking them to other African countries and to other continents. Previously international communication was by microwave links through geostationary satellites. These are becoming redundant...
ThunderKAT is one of ten accepted MeerKAT Large Survey Projects. ThunderKAT will study all aspects of transient radio emission associated with accretion and explosive events. Through a comprehensive and complementary programme of monitoring Galactic synchrotron transients (across a range of compact accretors and a range of other explosive phenomena) and exploring distinct populations of...
With the birth of the new generation ground-based gamma-ray imaging atmospheric Cherenkov telescope arrays (such as H.E.S.S., MAGIC and VERITAS), there is a growing need to probe X-ray binary stars for very high energy gamma-ray emissions. Since the discovery of the first extra-solar X-ray binary (XRB), namely the Scorpius X-1 in 1962, XRBs are now well-established systems in the realm of...
The Fermi Large Area Telescope (LAT) has revolutionized high-energy (HE) astronomy, and is making enormous contributions particularly to gamma-ray pulsar science. As a result of the many new pulsar discoveries, the gamma-ray pulsar population is now approaching 100. Some very famous millisecond pulsars (MSPs) have also been detected: J1939+2134 (a.k.a. B1937+21), the first MSP ever...
Since the launch of the Large Area Telescope (LAT) on board the Fermi spacecraft in June 2008, the number of observed gamma-ray pulsars has increased dramatically. A large number of these are also observed at radio frequencies. Weltevrede et al. (2010) derived constraints on the viewing geometries of 6 gamma-ray pulsars exhibiting single-peaked gamma-ray profiles using high-quality radio...
The highly transient novalike variable AE Aqr is perhaps an ideal laboratory to study accretion related astrophysical fluid dynamics. It consists of a fast spinning highly magnetic white dwarf (WD) orbiting, and accreting mass, from a low-mass main sequence companion. The system emits, and has been detected in almost all wavelengths. AE Aqr is in a propeller state, and most of its emission...
Some eclipsing contact binary stars of the W UMa-type are known to undergo changes in orbital period. These changes can be as a result of the light travel time effect if the contact binary is a member of a multiple stellar system or due to some intrinsic phenomena that are poorly understood at this stage. Analysing systems that appear to be undergoing changes in orbital period may shed...
Kazarovets et al. (1999) gave General Catalogue of Variable Star (GCVS) designations to 3157 variable stars that had been identified from observations made using the Hipparcos satellite. The variables were classified into standard GCVS categories according to their photometric light curves, but no other parameters of the variables were documented. V-band photometric data for many of the...
Pigulski and Kolaczkowski (2002, A&A 388, 88) announced the first discovery of Beta Cephei (BCep) pulsators in the LMC. This was a remarkable discovery, since theoretical analyses of pulsational stability had previously predicted that early B main-sequence stars with metallicities lower than Z = 0.01 should not pulsate at all (e.g. Pamyatnykh 1999, Acta Astron 49, 199). Following this...
I adapt a recent work by Zahn et al. on the shape of rapidly rotating stars to explore the degree of oblateness for uniform, differential and shellular rotation of the star. I also discuss the relation of these results to the classical Roche limit.
The cosmic microwave background (CMB) carries information from the last scattering surface that puts constraints on the multitude of proposed cosmological models and the gravity theories they are based on. Amongst such theories are the f(R) theories of gravity which have become an interesting endeavour to correct for the degeneracies of the concordance model. We present a description of...
The direct evidence for the acceleration of hadronic cosmic rays at supernova remnants underlined the need for a 3D time dependent treatment of the propagation of Galactic Cosmic Rays (CRs). Full 3D time dependent calculations of the propagation of CRs have shown that if CRs indeed originate from supernova remnants, transient point-like sources, the flux of the CR primary component measured...
A two-dimensional hydrodynamic numerical model is extended and applied to simulate the interaction between stellar winds and the interstellar medium (ISM). In particular, the stellar wind evolution of O-and B-type stars is calculated. First, the evolution of a stellar wind into the ISM and also a more dense molecular cloud are considered for the case of no relative motion between the star...
It is well known that neutron stars have very strong magnetic fields and that these fields impact the behaviour of the star. The focus of our research is on the interaction between the magnetic field and the constituent matter in the neutron star’s interior. In particular we investigate the possibility of a ferromagnetic phase in the neutron star interior being the source of the star’s...
In his work on superfluid helium, Feynman gave both qualitative and quantitative descriptions of the excitation spectrum of superfluid helium. I briefly review Feynman's approach to superfluid helium and assess the applicability of this theory to neutron star interiors.
The advent of the MeerKAT and SKA radio telescope projects will allow for vastly improved precision in the measurement of pulsar radio frequency emissions. Thus, the propagation of a pulsar’s conical radio beam through the strong gravitational field region in the vicinity of a compact object, i.e. black-hole or another neutron star, will probe the metric of spacetime in the high-field...
Applying the quantisation of action variables to a theory of gravitation one derives discrete values for planetary distances from the sun. The calculated values agree with the observed values of all the planets. The derived equation also applies to the exoplanets. The application is similar to that of the Wilson-Sommerfeld rule for atomic orbits.
Perturbation theory uses Lagrangian techniques that require vector fields to be compared at finitely separated points. This method can be generalised to the strong gravitational field regime in one of two ways, using either covariant or Lie derivatives. In this paper, I argue that those methods based on the Lie derivative are more useful. The Lie derivative provides a clear picture of how...
Genetic algorithms form a class of search heuristics that incorporate, in a computational setting, the biological notion of evolution by means of mutation and natural selection. Compared to more conventional search and optimisation techniques, genetic algorithms are very easy to implement and they tend to be extremely robust and versatile. Although already ubiquitous in fields such as...
To understand the formation of stars one must be able to identify young objects. RCW 34 is a star forming region in the constellation of Vela. A study was conducted in the near-infrared where it was found that a large number of stars surrounding the nebula shows NIR characteristics of lower mass pre-main sequence stars. To prove the suspicions a follow-up study was conducted in the optical....
We use the HI velocity profiles of The HI Nearby Galaxy Survey (THINGS) to study the phase structure of the ISM and its relation to galaxy properties and morphology. To construct high S/N profiles, we use a method analogous to the stacking method sometimes used in high redshift HI observations. We call these high S/N profiles super profiles. By decomposing the super profiles into Gaussian...
In this project data from The HI Nearby Galaxy Survey (THINGS) and from the HERA CO Extragalactic Line Survey (HERACLES) is being used to compare the HI (neutral hydrogen) and CO dispersions in nearby galaxies in order to see if they are related. This is important in improving star formation laws (as they currently only use HI dispersions, but stars form from molecular gas) and to better...
The aim of this project is to study the stellar populations, and thereby evolution and star formation histories of brightest cluster galaxies (BCGs). In particular, I will determine if a Single Stellar Populations (SSP) or Composite Stellar Populations (CSP) provides the most significant fit for the BCGs using high signal-to-noise ratio (S/N), long-slit spectra, obtained on the Gemini and...
A number of solutions to the dark energy problem have been proposed in literature, the simplest is the cosmological constant Λ. But the cosmological constant lacks theoretical explanation for its extremely small value, thus dark energy is more generally modeled as quintessence scalar field rolling down a flat potential. For the quintessence scalar field to be evolving on cosmological...
An ionospheric eight year study (2001-2008) over South Africa (SA) was conducted using ionosonde data observed by DPS-4 digisondes with a time resolution of 10, 15 and 30 minutes from Madimbo, Grahamstown and Louisvale. Spread F (SF) characterized by ionograms is observed when the pulses returned from the F region of the ionosphere are of longer duration than the transmitted signals....
The importance of calibrating satellite imagers has been explained in literature such as K Arai (2007) and K J Thome (2001). Calibration of satellite sensors (imagers) is crucial for data consistency, reliability and comparability. To perform a meaningful analysis of a satellite image, the Digital Numbers (DNs) of the image are first converted to absolute radiance by using the...
Satellites have to operate in a hostile space environment that poses numerous threats from radiation, charged particles, residual atmosphere, micrometeoritic impacts, space debris and other operational and defunct satellites. The region of outer space around the Earth is becoming polluted from anthropogenic space system junk and fragments. Currently, according to US Space Surveillance...
A magnetized dusty plasma composed of an adiabatic negatively charged dust fluid, Boltzmann ions and Boltzmann electrons is considered for which coupled nonlinear dust-acoustic and dust-cyclotron waves hav- ing sinusoidal, sawtooth or spiky electric field waveforms are found to be supported when charge neutrality is assumed (Maharaj et al, 2008). The focus of this investigation is to...
We study the generation of Pc3 geomagnetic pulsations (22 – 100 mHz) measured at Tihany, Hungary during intervals of very low solar wind (SW) proton density (low density events - LDE’s) when Np ~ 1/cc. We know the main SW based drivers of Pc3's are SW velocity and interplanetary magnetic field (IMF) direction. However, it is observed that under very low SW density pulsation activity...
In 1958, Eugene Parker predicted that the outer parts of the Sun's atmosphere, the solar corona, must be expanding in the form of a supersonic solar wind. This was confirmed by the Mariner 2 spacecraft in 1962. On 16 December 2004, the Voyager 1 spacecraft crossed the heliospheric termination shock, where the flow becomes subsonic, and began exploring the heliosheath. In August 2007,...
We investigate cosmic-ray intensities as measured by neutron monitors as function of the corresponding heliospheric current sheet tilt angle. Three solar cycles with three changes in solar magnetic polarity are examined. The results are compared to predictions of cosmic-ray modulation models that include drift effects. The intensity-tilt plots produce open loops with clockwise rotations for...
Solutions of General Relativity Theory (GRT) pertaining to space geodesy are weak field, slow motion approximations. These approximations are valid as the gravitational field in which the solutions are performed has a potential of small magnitude and the velocities involved for any of the satellites are much smaller than the velocity of light. The basic effects of GRT on space geodetic...
Lightning induced whistler waves are one of the primary causes of energetic electron loss from the Earth's radiation belts. This is mainly due to the pitch angle scattering of the particles by whistler mode waves, leading to precipitation. The detailed spatial and temporal influence of lightning on precipitation losses is, however, not well known. The World Wide Lightning Location Network...
The OMNI-2 data set enables a correlation study of solar wind and geomagnetic parameters, allowing the stream Interfaces events (SIs) to be examined. A superposed epoch analysis of these events was performed to determine the threshold levels of IMF Bz and other geophysical parameters. Based on energy, temporal and spatial characteristics, statistical analysis of electron flux data from...
Markarian 926 (= MCG-2-58-22) is one of the earliest Seyfert galaxies identified. At discovery it was one of the most luminous nearby active galactic nuclei (AGN), with strong, wide broad lines. In the late 1980's it started fading, eventually settling at barely ~10% of its recorded peak luminosity. The luminosity decrease was accompanied by significant spectral changes, with the broad-line...
