Artists impression of an Exoplanet orbiting a star

Congratulations to Guildford AS which is one of the first UK societies to have detected the light signature of an exoplanet orbiting a star.  This is a fantastic achievement.  The following repot was provided by Tony Marsh.

An exoplanet is a planet going round another star rather than the Sun.

Nobody including the Hubble Space Telescope can yet take a picture of an Exoplanet.  However, many artists’ impressions have been made like this one.There are several methods of detecting exoplanets. The one amateur astronomers can try is to look for a dip in the brightness of the star as the planet passes between the star and the Earth. The dip in brightness is very small, typically the light drops from 100% to 99.95%. It has been likened to observing a flea crossing a car headlight from a mile away.

On the 27th September 2011 GAS astronomers detected their first exoplanet. The star the planet goes round is almost the twin of our Sun. It is 19.3 light years away from Earth. The star is located very close to the Dumbbell Nebula, M27 in the constellation of Vulpecia. You can see M27 in the picture below together with the exoplanet star and the reference stars used to compare with the brightness of the exoplanet star HD189733. We used a software package called AIP4WIN to do the analysis of all the stars brightness.

Star map - locating the exoplanet star
Star map - locating the exoplanet star (Click to enlarge)

Previous professional observations have shown the planet to be a little bigger and heavier than Jupiter so it is a GAS giant! However, it takes only 2¼ days to go round its star, that is to say its year is only 2¼ days long. Mercury takes 88 days to go round the Sun. The exoplanet must be being cooked by its star and its atmosphere is probably boiling away leading to ferocious winds of thousands of miles an hour. Not somewhere you would want to live.

Using the GAS imaging observatory a group of 7 GAS astronomers recorded the star’s brightness and detected the exoplanet.

As you can see in the diagram the light from the star dipped as the exoplanet transited the star in just under 2 hours. We followed the star for over three hours or over 45 degrees.

The light curve
Image of the recorded light curve

This shows our results submitted to the Exoplanet Transit Database, (ETD), an international database of amateur and professional observers maintained in the Czech Republic. We removed our trend in magnitude between HD189733, 7.67 mag, type G5, and the reference stars before subm,ission to the database. The reference stars were HD189657 which is a A0 star Mag 8.10 and HD345459 which is a K0 star Mag 8.19. The computer model of the transit that ETD use fits our data quite well as you can see from the diagram. Thus confirming that we did indeed observe an exoplanet. A quick look at the ETD database shows lots of observations of many exoplanets by amateurs around the world but surprisingly very few from the UK. Come on guys, – where are you?

Picture of the exoplanet team
The exoplanet team


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