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