Modelling of W UMa-type Variable Stars Patricia Skelton MScUNISA Prof. Derck Smits SKA Postgraduate Bursary Conference The Wallenberg Centre, stis 1 – 5 December 2008
Over-Contact System
Properties of W UMa-type Stars Overcontact binary: Common Envelope binary Envelope binary Period < 1 day Spectral Range: A - K Δ T approximately a few hundred degrees degrees Subclasses : A-Type and W-Type
ASAS Las Campanas Observatory, Chile 7cm aperture telescope Observe once every 1 – 3 days 50,000+ variable stars discovered Over 5000 are EW stars
SuperWASP Monitor sky for planetary transits Two robotic observatories: North: La Palma, South: SAAO North: La Palma, South: SAAO Eight wide angle cameras. Camera aperture 11.1cm Observe on a daily basis
ASAS WASP
PHOEBE
Stars Of Interest Stars that display period changes Stars that may be magnetically active: Search for radio emission Previous surveys for radio emission used distance as a search criterion. Flare detected from VW Cep. Goal: Evidence for magnetic activity in light curves.
The O’Connell Effect Maxima Different Height Magnetic Activity: Spots
Flux Changes ASAS ASAS Decrease in flux Increase in flux
Flux Changes ASAS ASAS data WASP data Combined increase & decrease in flux
Interesting star ASAS
Period Changes ASAS Data WASP Data
Unanswered Questions EW stars: How do they form and what do they become? Complex pattern of period changes Common Envelope: Uniform temperature. Why?
Future Research Period changes: O-C diagram APT observations Radial velocity measurements: Mass ratios Surveys for radio emission from spots: VLA, SKA
Image adapted from Binary Maker 3