Modelling of W UMa-type Modelling of W UMa-type Variable StarsVariable Stars

Patricia SkeltonPatricia Skelton

MScMSc

UNISAUNISA

Prof. Derck SmitsProf. Derck Smits

SKA Postgraduate Bursary ConferenceSKA Postgraduate Bursary Conference

The Wallenberg Centre, stiThe Wallenberg Centre, stiss

1 – 5 December 20081 – 5 December 2008

Over-Contact SystemOver-Contact System

Properties of W UMa-type StarsProperties of W UMa-type Stars

Overcontact binary:Overcontact binary: Common Common Envelope binaryEnvelope binary Period < 1 dayPeriod < 1 day Spectral Range: A - K Spectral Range: A - K ΔΔT approximately a few hundred T approximately a few hundred degreesdegrees Subclasses : A-Type and W-TypeSubclasses : A-Type and W-Type

ASASASAS Las Campanas Observatory, ChileLas Campanas Observatory, Chile 7cm aperture telescope7cm aperture telescope Observe once every 1 – 3 daysObserve once every 1 – 3 days 50,000+ variable stars discovered50,000+ variable stars discovered Over 5000 are EW starsOver 5000 are EW stars

SuperWASPSuperWASP

Monitor sky for planetary transitsMonitor sky for planetary transits Two robotic observatories:Two robotic observatories:

North: La Palma, South: SAAONorth: La Palma, South: SAAO Eight wide angle cameras. Camera Eight wide angle cameras. Camera

aperture 11.1cmaperture 11.1cm Observe on a daily basisObserve on a daily basis

ASAS

WASP

PHOEBEPHOEBE

Stars Of InterestStars Of Interest

Stars that display period changesStars that display period changes Stars that may be magnetically Stars that may be magnetically

active: Search for radio emissionactive: Search for radio emission Previous surveys for radio emission Previous surveys for radio emission

used distance as a search criterion. used distance as a search criterion. Flare detected from VW Cep.Flare detected from VW Cep.

Goal: Evidence for magnetic activity Goal: Evidence for magnetic activity in light curves.in light curves.

The O’Connell EffectThe O’Connell Effect

Maxima Different HeightMaxima Different Height Magnetic Activity: SpotsMagnetic Activity: Spots

Flux ChangesFlux Changes

8.3

8.35

8.4

8.45

8.5

8.55

8.6

8.65

1750 1950 2150 2350 2550 2750 2950 3150 3350 3550 3750

HJD ( + 2450000)

Mag

nit

ud

e

ASAS 133246-1745.5

10.4

10.5

10.6

10.7

10.8

10.9

11

11.1

1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800

HJD ( + 2450000)

Mag

nit

ud

e

ASAS 062426-2044.9

Decrease in flux

Increase in flux

Flux ChangesFlux Changes

9.7

9.8

9.9

10

10.1

10.2

10.3

10.4

1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800

HJD ( + 2450000)

Mag

nit

ud

e

9.8

9.9

10

10.1

10.2

10.3

10.4

10.5

3850 3900 3950 4000 4050 4100

HJD ( + 2450000)

Mag

nit

ud

e

ASAS 002328-2041.8ASAS 002328-2041.8

ASAS dataASAS data

WASP dataWASP data

Combined increase & decrease in flux

Interesting starInteresting star

ASAS 002328-2041.8

Period ChangesPeriod Changes

ASAS Data

WASP Data

Unanswered QuestionsUnanswered Questions

EW stars: How do they form and EW stars: How do they form and what do they become?what do they become?

Complex pattern of period changesComplex pattern of period changes Common Envelope: Uniform Common Envelope: Uniform

temperature. Why?temperature. Why?

Future ResearchFuture Research

Period changes: O-C diagramPeriod changes: O-C diagram APT observationsAPT observations Radial velocity measurements: Mass Radial velocity measurements: Mass

ratiosratios Surveys for radio emission from Surveys for radio emission from

spots: VLA, SKAspots: VLA, SKA

Image adapted from Binary Maker 3