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Transcript 
Modelling of W UMa-type
Variable Stars
Patricia Skelton
MSc
UNISA
Prof. Derck Smits
SKA Postgraduate Bursary Conference
The Wallenberg Centre, stis
1 – 5 December 2008
Over-Contact System
Properties of W UMa-type Stars





Overcontact binary: Common
Envelope binary
Period < 1 day
Spectral Range: A - K
ΔT approximately a few hundred
degrees
Subclasses : A-Type and W-Type
ASAS





Las Campanas Observatory, Chile
7cm aperture telescope
Observe once every 1 – 3 days
50,000+ variable stars discovered
Over 5000 are EW stars
SuperWASP
Monitor sky for planetary transits
 Two robotic observatories:
North: La Palma, South: SAAO
 Eight wide angle cameras. Camera
aperture 11.1cm
 Observe on a daily basis

ASAS
WASP
PHOEBE
Stars Of Interest
Stars that display period changes
 Stars that may be magnetically
active: Search for radio emission
 Previous surveys for radio emission
used distance as a search criterion.
Flare detected from VW Cep.
 Goal: Evidence for magnetic activity
in light curves.

The O’Connell Effect


Maxima Different Height
Magnetic Activity: Spots
Flux Changes
HJD ( + 2450000)
1750
1950
2150
2350
2550
2750
2950
3150
3350
3550
3750
8.3
ASAS 133246-1745.5
8.35
Magnitude
8.4
8.45
Decrease in flux
8.5
8.55
8.6
8.65
HJD ( + 2450000)
1800
10.4
10.5
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
ASAS 062426-2044.9
Magnitude
10.6
10.7
10.8
10.9
11
11.1
Increase in flux
Flux Changes
HJD ( + 2450000)
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
ASAS 002328-2041.8
3800
9.7
9.8
Magnitude
9.9
ASAS data
10
10.1
10.2
10.3
10.4
Combined increase
& decrease in flux
HJD ( + 2450000)
3850
9.8
3900
3950
4000
4050
4100
9.9
Magnitude
10
10.1
10.2
10.3
10.4
10.5
WASP data
Interesting star
ASAS 002328-2041.8
Period Changes
ASAS Data
WASP Data
Unanswered Questions



EW stars: How do they form and
what do they become?
Complex pattern of period changes
Common Envelope: Uniform
temperature. Why?
Future Research
Period changes: O-C diagram
 APT observations
 Radial velocity measurements: Mass
ratios
 Surveys for radio emission from
spots: VLA, SKA

Image adapted from Binary Maker 3
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