1. Period Analysis of Eclipsing Binaries Patricia Skelton MSc Prof. D.P. Smits UNISA SKA Postgraduate Bursary Conference The Wallenberg Centre, stis 5 December 2009

2. W UMa-type Variable Stars 2 Common Envelope Binaries Binaries P < 1 day P < 1 day Spectral Range A – K ΔK ≈ few hundred ΔK ≈ few hundred degrees degrees

3. W UMa-type Variable Stars 3

4. Sources of Data 4 ASAS Enclosure Las Campanas, Chile SuperWASP South SAAO, Sutherland All Sky Automated Survey Wide Angle Search for Planets

5. Sources of Data 5 ASAS SuperWASP

6. Period Analysis Changes in orbital period: may be a result of mass transfer or LTTE Changes in orbital period: may be a result of mass transfer or LTTE O – C diagram used to determine if period is changing O – C diagram used to determine if period is changing 6

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8. 8 Var(T min )

9. O – C Diagram: Part 1 9 P = 0.313670 d Used T min and ASAS P to construct O – C diagram Used T min and ASAS P to construct O – C diagram Correct period: O – C values scattered about O – C = 0 Correct period: O – C values scattered about O – C = 0 Positive or Negative slope – Different period Positive or Negative slope – Different period (O – C) = T min – T 0 – εP (O – C) = T min – T 0 – εP

10. Least Squares Analysis Analysis returns a new P and T 0 Analysis returns a new P and T 0 Obtain linear or quadratic ephemeris: Obtain linear or quadratic ephemeris: T min = T 0 + εP T min = T 0 + εP T min = T 0 + εP + aε 2 T min = T 0 + εP + aε 2 Constructed new O – C diagrams Constructed new O – C diagrams 10

11. O – C diagram: Part 2 11 Linear Ephemeris : P = 0.31366012 d Σ(O – C) 2 = 3.22 × 10 -6 Quadratic Ephemeris : P = 0.3136592 d Σ(O – C) 2 = 2.94 × 10 -6

12. ASAS 002328-2041.8 12

13. Way Forward - PhD Continue monitoring stars of interest Continue monitoring stars of interest Automate the procedures of the period analysis Automate the procedures of the period analysis Extend project to a multi-wavelength study – Infrared, X-ray and Radio Extend project to a multi-wavelength study – Infrared, X-ray and Radio Stars modelled with stellar spots – potential targets for observations with the SKA Stars modelled with stellar spots – potential targets for observations with the SKA 13

14. THANK YOU!

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17. Summary - MSc Modelled selected ASAS contact binary stars Modelled selected ASAS contact binary stars 1 shallow-contact, 1 deep-contact 1 shallow-contact, 1 deep-contact Stellar spots improved models of 2 stars Stellar spots improved models of 2 stars Period analysis of 8 contact binaries Period analysis of 8 contact binaries 5 systems – period decreased 5 systems – period decreased 3 systems – period increased 3 systems – period increased 17

18. Minima Influenced by Spots Stellar spots can affect shapes of minima.Stellar spots can affect shapes of minima. 18

19. Step 1: Time of minimum Small phase interval, minimum parabolic in shape Small phase interval, minimum parabolic in shape Second-order polynomial: Second-order polynomial: 19

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21. Minima Influenced By Spots Stellar spots can affect shapes of minima.Stellar spots can affect shapes of minima. Asymmetrical minima can be useful when modelling systems.Asymmetrical minima can be useful when modelling systems. Help to identify systems that are magnetically active.Help to identify systems that are magnetically active. 21

22. 22 ASAS 150452-3757.7 ASAS 150934-3348.5