period analysis of eclipsing binaries patricia skelton msc prof. d.p. smits unisa ska postgraduate...

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