period analysis of eclipsing binaries patricia skelton msc prof. d.p. smits unisa ska postgraduate...
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Period Analysis of Eclipsing Binaries
Patricia Skelton
MSc
Prof. D.P. Smits
UNISA
SKA Postgraduate Bursary ConferenceThe Wallenberg Centre, stis
5 December 2009
W UMa-type Variable Stars
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• Common Envelope
Binaries• P < 1 day
• Spectral Range A – K
• ΔK ≈ few hundred degrees
W UMa-type Variable Stars
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Sources of Data
4ASAS EnclosureLas Campanas, Chile
SuperWASP SouthSAAO, Sutherland
All Sky Automated Survey Wide Angle Search for Planets
Sources of Data
5ASAS SuperWASP
Period Analysis
• Changes in orbital period: may be a result of mass transfer or LTTE
• O – C diagram used to determine if period is changing
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Var(Tmin)
O – C Diagram: Part 1
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P = 0.313670 d
• Used Tmin and ASAS P to construct O – C diagram
• Correct period: O – C values scattered about O – C = 0
• Positive or Negative slope – Different period
• (O – C) = Tmin – T0 – εP
Least Squares Analysis
• Analysis returns a new P and T0
• Obtain linear or quadratic ephemeris:
• Tmin = T0 + εP
• Tmin = T0 + εP + aε2
• Constructed new O – C diagrams
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O – C diagram: Part 2
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Linear Ephemeris :P = 0.31366012 dΣ(O – C)2 = 3.22 × 10-6
Quadratic Ephemeris :P = 0.3136592 dΣ(O – C)2 = 2.94 × 10-6
ASAS 002328-2041.8
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Way Forward - PhD
• Continue monitoring stars of interest
• Automate the procedures of the period analysis
• Extend project to a multi-wavelength study – Infrared, X-ray and Radio
• Stars modelled with stellar spots – potential targets for observations with the SKA
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THANK YOU!
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Summary - MSc
• Modelled selected ASAS contact binary stars• 1 shallow-contact, 1 deep-contact
• Stellar spots improved models of 2 stars
• Period analysis of 8 contact binaries• 5 systems – period decreased
• 3 systems – period increased
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Minima Influenced by Spots
• Stellar spots can affect shapes of minima.
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Step 1: Time of minimum
• Small phase interval, minimum parabolic in shape
• Second-order polynomial:
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Minima Influenced By Spots
• Stellar spots can affect shapes of minima.
• Asymmetrical minima can be useful when modelling systems.
• Help to identify systems that are magnetically active.
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ASAS 150452-3757.7
ASAS 150934-3348.5