1. Modelling of W UMa-type Variable Stars Patricia Skelton MScUNISA Prof. Derck Smits SKA Postgraduate Bursary Conference The Wallenberg Centre, stis 1 – 5 December 2008

2. Over-Contact System

3. 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

4. ASAS  Las Campanas Observatory, Chile  7cm aperture telescope  Observe once every 1 – 3 days  50,000+ variable stars discovered  Over 5000 are EW stars

5. 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

6. ASAS WASP

7. PHOEBE

8. 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.

9. The O’Connell Effect  Maxima Different Height  Magnetic Activity: Spots

10. Flux Changes ASAS 133246-1745.5 ASAS 062426-2044.9 Decrease in flux Increase in flux

11. Flux Changes ASAS 002328-2041.8 ASAS data WASP data Combined increase & decrease in flux

12. Interesting star ASAS 002328-2041.8

13. Period Changes ASAS Data WASP Data

14. Unanswered Questions  EW stars: How do they form and what do they become?  Complex pattern of period changes  Common Envelope: Uniform temperature. Why?

15. Future Research  Period changes: O-C diagram  APT observations  Radial velocity measurements: Mass ratios  Surveys for radio emission from spots: VLA, SKA

16. Image adapted from Binary Maker 3