Asteroseismology Research Group

Dr CA Engelbrecht leads the asteroseismology group at UJ, which works closely with colleagues at the University of the Witwatersrand, the South African Astronomical Observatory (SAAO) and the ARIES Institute in India. We also have collaborations with astronomers in Belgium, Denmark, Poland and Turkey in place. The group has adopted a comprehensive approach to this research, including: i) an intensive observing programme; ii) ongoing work in refining the analysis of time series, using the 280-node fast computing cluster at UJ; iii) an innovative theory programme in stellar structure and evolution. We obtain data from South African and Indian ground-based telescopes, as well as using the rich database of the Kepler space telescope. Six South African students are working on MSc or PhD projects in the group during 2013. We successfully applied for 3 rounds of spectroscopic time on the SALT facility at Sutherland in 2012-13.  The specific topics that are being studied actively in 2013 include: pulsation mode identification of B, A and F stars in general, the effect of metallicity on pulsations of hot stars in the LMC, tidally-induced resonances between orbital motion and pulsations in Algol-type binary systems, radial velocity cross-correlation in Algol systems, the effects of stellar rotation on pulsations, the implementation of Reynolds Stress Methodology (RSM) in the modeling of convective energy transfer in hot stars, modeling of tidally-induced pulsation in the components of binary systems and modeling of stellar rotation. The group has published 16 papers in the field since 2011.  More information may be found on the Asteroseismology link.

Dr Engelbrecht also serves on the science team of the TRAPUM large survey project that has been allocated 3000 hours of observing time on the MeerKAT radio telescope array being constructed in the Northern Cape. This array will eventually be incorporated into Phase 1 of the SKA medium-frequency array, but is anticipated to work as an independent array for about 10 years once it becomes fully operational around 2016. Dr Engelbrecht will work with Dr Frescura  of Wits on theoretical modeling of transients and pulsars discovered by the TRAPUM survey.

Dr Engelbrecht has played an integral role in expanding the National Astrophysics and Space Science Programme (NASSP) to other parts of the country. He regularly teaches courses in the NASSP and serves on the NASSP Steering Committee as well as on the Sutherland Telescope Users Committee (STUC). Dr Engelbrecht will be teaching the Stellar Structure and Evolution course in the Honours programme at UJ from 2014 onward.


Dr CA Engelbrecht (UJ group leader)
Mr CT Middleton (PhD student)
Mr HP van Heerden (PhD student)
Ms RG Kgoadi (MSc student)


Associate researchers outside UJ:
Dr FAM Frescura (Senior lecturer,WITS)
Dr LA Balona (Honorary Researcher, South African Astronomical Observatory)
Dr Peter Martinez (Astronomer, South African Astronomical Observatory)
Dr Y Joshi (Scientist, Aryabhatta Research Institute of Observational Sciences, Nainital, India)
Dr S Joshi (Scientist, Aryabhatta Research Institute of Observational Sciences, Nainital, India)
Dr D Sürgit (Lecturer, Canakkale Onsekiz Mart University, Canakkale, Turkey)

South African students outside UJ:
Mr SL Moonsamy (PhD student, WITS)
Mr M Predieri (MSc student, WITS)
Mr M Johnson (MSc student, WITS)

The Asteroseismology Research Group conducts three research programmes in parallel: An observing programme, a theory programme and a time series analysis programme. - The observing programme is focused on pulsating B, A and F stars of various types. In particular, we are exploring how stellar pulsations are affected by metallicity, stellar rotation and binarity respectively. We have an observing programme running at the South African Astronomical Observatory in the Northern Cape and various telescope sites in India. In addition, we have been making intensive use of Kepler space telescope observations through our membership of the Kepler Asteroseismic Science Consortium (KASC)  since 2010.

 

  • The theory programme has two distinct components. The first is mainly focused on exploring the description of convection, turbulence and rotation in stellar interiors. In particular, we are developing algorithms for the numerical calculation of the effects of the abovementioned physical processes on stellar structure and evolution. The aim of this work is to develop diagnostic tools for asteroseismology by calculating the effects of these processes on pulsation frequencies, amplitudes and phases. 
  • The other component of our theory work is focused on exploring neutron star interiors and the exterior environments of pulsars, respectively. Recent projects include a quantum-field-mechanical description of superfluid vortex arrays in neutron stars and the effects of very strong gravitational fields on pulsar radiation in a black hole – pulsar binary system.
  • The programme on time series analysis is focused on exploring various approaches to time series analysis of unequally-spaced data. We run Monte Carlo simulations on the 280-node computing cluster at UJ as part of this programme.

 

An 8-day workshop on Convection in Stars was organised by Dr Frescura and Dr Engelbrecht, with much assistance from Prof RT Medupe (NWU) and Dr E Olivier (SAAO) and hosted in Council Chambers at UJ during the first two weeks of January 2011. The workshop turned into a master class in the theory of convection and turbulence in stellar plasmas, thanks to the remarkable series of lectures prepared and delivered by uncontested luminaries in the field of stellar convection: Emeritus Professor Douglas Gough (University of Cambridge), Professor Vittorio Canuto (Columbia University and NASA Goddard Institute of Space Studies), Professor Jørgen Christensen-Dalsgaard (Århus University, Denmark) and Dr Günter Houdek (Institute for Astronomy, University of Vienna). The workshop drew 31 participants of whom 16 were students. The workshop received funding from the National Institute for Theoretical Physics (NITheP) and from WITS. The group’s current work on Reynolds Stress Methodology (RSM) as an approach for more accurate modeling of convective energy transfer in stars is a direct result of this workshop. Mr SL Moonsamy, a PhD student in the group, will be joining a development workshop of the MESA (Modules for Experiments in Stellar Astrophysics) collaboration at the University of California at Berkeley late in 2013, specifically to contribute his work on RSM.

Establishing two projects on the Indo-South African Astronomy Collaboration platform

Dr Engelbrecht recently visited the ARIES institute in India to formally establish the UJ group as participants in two asteroseismology projects under the formal India-South Africa intergovernmental collaboration agreement in science. The projects are envisaged to run until 2017, with possible extensions thereafter.

     
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