SuperWASP Observations of Variable Stars

SuperWasp

WASP stands for the Wide Angle Search for Planets. It consists of two robotic observatories, one in the northern hemisphere on the island of La Palma and one in the southern hemisphere locate just outside Sutherland, South-Africa, that operate all year round. SuperWASP is the UK's leading extra-solar planet detection program, which is made up of eight academic institutions - Cambridge University, the Instituto de Astrofisica de Canarias, the Isaac Newton Group of telescopes, Keele University, Leicester University, the Open University, Queen's University Belfast and St. Andrew's University. They search for planets by looking for 'transits'. These occur when a planet goes in front of its parent star (the star it is orbiting) and obscures some of its light. We can detect this from Earth if we analyse the light-curves of stars. If we look at the light-curve of a star we can see a 'dip' in the brightness if there is a planet that crosses over it. It sounds easy, but the change a planet can make to a star's light curve can be incredibly small, so it is essential to take accurate measurements. On top of this, many stars are variable, so the light-curves are not straight lines to begin with. It is important to have a good understanding of the different types of variable stars and their light-curves, so that precious and expensive time on larger telescopes is not wasted.

Here are some examples of light-curves from the stars that SuperWASP have found planets orbiting. The dips in the light-curve is when the planet is orbiting in front of the star in our plane of sight:

WASP-2

WASP-4

WASP-10

Variable Stars

A variable star is one that undergoes significant variation in its luminosity. There are two main types of variable star: intrinsic and extrinsic.

Intrinsically variable stars luminosity physically changes in pulsating variables, where stars show periodic expansion and contraction of their surface layers; eruptive variables, where stars vary in brightness because of violent processes and flares occurring in the chromosphere (a thin, hot layer just above the visible photosphere); or cataclysmic variables.

The apparent variabilities in the brightness of extrinsic stars are a perspective effect such as eclipsing binary and rotating stars.

To find out more click on a variable:



Made by Natalie Wilson, Year 10 from Alleyne's High School



Bibliography:

http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_pulsating.html

http://www.sai.msu.su/groups/cluster/gcvs/gcvs/iii/vartype.txt

http://imagine.gsfc.nasa.gov/

http://www.superwasp.org/