A study of young supernova remnants

This thesis is submitted in accordance to the University of Western Sydney's thesis rules for ‘Thesis as a Series of Papers’. This thesis comprises four lead author and twenty-seven co-authored refereed journal papers published during my candidature. The theme of the papers and thus the thesis is a study supernova remnants (SNRs), in particular ‘young’ SNRs, that is SNRs <2000 years old representing the time of the transition from Supernova to Supernova Remnant. New high resolution Australia Telescope Compact Array radio-continuum observations and multifrequency archival data from various national and international observatories are used. Considered is how the SNRs' multifrequency morphological appearance, polarisation and magnetic field relates to their age, stage of evolution and progenitor star explosion mechanism

Radio Planetary Nebulae in the Magellanic Clouds

We present preliminary results of our deep Australia Telescope Compact Array (ATCA) radio-continuum survey of the Magellanic Clouds Planetary Nebulae.Comment: 2 pages 1 figure, to appear in Planetary Nebulae an Eye to the Future Proceedings IAU Symposium No. 28

A Study of Twelve Potential Merger Candidate Contact Binary Systems

Photometric observations and analysis of twelve previously poorly studied contact binary systems is presented. All show total eclipses and have extremely low mass ratios ranging from 0.072 to 0.15. Also, all show characteristics of orbital instability with mass ratios within the theoretical orbital instability range. Although none demonstrate a significant O'Connell effect at least nine of the systems have other indicators of increased chromospheric and magnetic activity.Comment: 11 Pages, 2 Figures Accepted Publications of the Astronomical Society of the Pacific (PASP

Effects of Metallicity on the Instability Mass Ratio of Low Mass Contact Binary Systems

The orbital stability of contact binary systems has been receiving considerable attention recently. Theoretical studies indicate that merger is likely to occur at very low mass ratios, but the actual mass ratio at which merger may take place is likely to be variable and dependent on the mass of the primary. We consider the effects of metal content on the orbital stability of contact binary systems by modelling the gyration radius of a rotating and tidally distorted primary component at various values of metallicity in the range -1.25 to +0.5. We determine the instability mass ratio range for contact binary systems with a low mass primary in the range 0.6M(sun) to 1.4M(sun) at various metallicity levels and show that systems with low metallicity have an instability mass ratio lower than those with higher metal content and therefore are likely to be more stable. We illustrate the effect through light curve analysis of two otherwise very similar contact binary systems, except for different metallicity. While both would be considered unstable if metallicity was not taken into consideration, only one remains in that category after appropriate adjustments based on metallicity have been made.Comment: 9 pages, 7 Figures and 5 Tables Accepted Monthly Notices of Royal Astronomical Society (MNRAS

Radio-Continuum Study of the Nearby Sculptor Group Galaxies. Part 2: NGC 55 at {\lambda}=20, 13, 6 and 3 cm

A series of new radio-continuum ({\lambda}=20, 13, 6 and 3 cm) mosaic images focused on the NGC55 galactic system were produced using archived observational data from the Australia Telescope Compact Array. These new images are both very sensitive (down to rms=33 {\mu}Jy) and feature high angular resolution (down to <4"). Using these newly created images, 66 previously unidentified discrete sources are identified. Of these sources, 46 were classified as background sources, 11 as HII regions and 6 as supernova remnant candidates. This relatively low number of SNR candidates detected coupled with the low number of large HII regions is consistent with the estimated low star formation rate of the galaxy at 0.06 solar masses per year. Our spectral index map shows that the core of galaxy appears to have a shallow spectral index between {\alpha} = -0.2 and -0.4. This indicates that the core of the galaxy is a region of high thermal radiation output.Comment: 11 pages, 8 figures. Accepted for publication in Astrophysics and Space Scienc

O debate sobre os métodos de ensino nos liceus portugueses (anos 30 a 60 do século XX)

Congresso realizado nos dias 6 a 9 de Maio de 2014, em Toluca, MéxicoA presente comunicação tem como objetivo refletir sobre os métodos de ensino, ao nível do ensino secundário, tal como são propostos e debatidos por educadores e professores em duas das grandes revistas pedagógicas consagrados a esse nível de ensino e ligadas a um importante contexto de formação de professores – o Liceu Normal de Pedro Nunes situado em Lisboa. Estamos a falar do Boletim do Liceu Normal de Lisboa Pedro Nunes (1932-1938) e de Palestra. Revista de pedagogia e cultura (1957-1973).info:eu-repo/semantics/publishedVersio

Development of a virtual reality overlay for Velnet (Virtual environment for learning networking)

The problems of providing a real, physical specialist laboratory to teach computer networking such as, the lack of funding and physical space and the risks and threats to the network environment and infrastructure, can be solved by the use of a virtual learning environment. Velnet is such a virtual learning environment that we have developed and used successfully. Velnet consists of one or more host machines and operating systems, commercial virtual machine software, virtual machines and their operating systems, a virtual network connecting the virtual machines, and remote desktop display software. In order to be able to present more computer-networking concepts and to improve on our original version of Velnet we have been developing a virtual reality overlay. This virtual reality overlay allows students to build virtual networking topologies in a virtual lab. This paper describes Velnet our virtual environment for learning networking and the virtual reality overlay currently under development

Polarized reflected light from the Spica binary system

Close binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (alpha Virginis) consisting of two B-type stars orbiting with a period of just over four days. Past observations of Spica have shown low poClose binary systems often show linear polarization varying over the binary period, usually attributed to light scattered from electrons in circumstellar clouds. One of the brightest close binary systems is Spica (alpha Virginis) consisting of two B-type stars orbiting with a period of just over four days. Past observations of Spica have shown low polarization with no evidence for variability. Here we report new high-precision polarization observations of Spica that show variation with an amplitude of about 200 parts per million. By including polarized radiative transfer in a binary star model, we show that the phase-dependent polarization is mainly due to light reflected from the primary component of the binary system off the secondary component and vice versa. The stars reflect only a few per cent of the incident light, but the reflected light is very highly polarized. The polarization results show that the binary orbit is clockwise and the position angle of the line of nodes is 130.4° ± 6.8°, in agreement with intensity interferometer results. We suggest that reflected light polarization may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries.arization with no evidence for variability. Here we report new high-precision polarization observations of Spica that show variation with an amplitude of about 200 parts per million. By including polarized radiative transfer in a binary star model, we show that the phase-dependent polarization is mainly due to light reflected from the primary component of the binary system off the secondary component and vice versa. The stars reflect only a few per cent of the incident light, but the reflected light is very highly polarized. The polarization results show that the binary orbit is clockwise and the position angle of the line of nodes is 130.4° ± 6.8°, in agreement with intensity interferometer results. We suggest that reflected light polarization may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries

HIPPI-2 : a versatile high-precision polarimeter

We describe the High-Precision Polarimetric Instrument-2 (HIPPI-2) a highly versatile stellar polarimeter developed at the University of New South Wales. Two copies of HIPPI-2 have been built and used on the 60-cm telescope at Western Sydney University's (WSU) Penrith Observatory, the 8.1-m Gemini North Telescope at Mauna Kea and extensively on the 3.9-m Anglo-Australian Telescope (AAT). The precision of polarimetry, measured from repeat observations of bright stars in the SDSS g′band, is better than 3.5 ppm (parts per million) on the 3.9-m AAT and better than 11 ppm on the 60-cm WSU telescope. The precision is better at redder wavelengths and poorer in the blue. On the Gemini North 8-m telescope, the performance is limited by a very large and strongly wavelength-dependent TP that reached 1000's of ppm at blue wavelengths and is much larger than we have seen on any other telescope