Introduction to Exo Planets
(Artist impression of an Exo planet around its host star)
Exo Planets are those planets orbiting stars other than our sun, often forming planetary systems around a host star as they do in our solar system.
The first Exo Planet was confirmed in 1995 and since then over 2000 have been discovered by large ground based telescopes and the Kepler space telescope, the latter discovering the majority.
Only a handful have ever been imaged, even by the largest telescopes man has developed. There are instead two indirect methods of detection. The first is to measure the minute ‘wobble’ in the star as a planet moves around its host, using the Doppler shift. The second and most common method is the ‘transit method’. Given the planet passes in front of the host star in the line of site of Earth, then the minute dimming of the total starlight reaching Earth can be measured.
By using one of more methods many things can be deduced, such as the planet size, distance from the host star the orbit period, or ‘year’.
It is possible for amateurs to detect some of these Exo planets using the transit method and if accurate enough to contribute to the pool of knowledge.
Myself and a colleague Ben Filmore, using my equipment started to investigate if we could detect and eventually contribute to the knowledge of Exo Planets. Starting in the springr of 2015 we first attempted to detect an Exo Planet known as TrES2.
We used published data by a highly successful amateur Exo Planet hunter, Brian Gray, in order to predict the transit time.
We were delighted to find that we secured a light curve confirming that we were able to detect Exo planets of a certain size. This has led us to work on a few more most notably HD189733, the data of which is shown below.
In the summer of 2016 we plan to attempt to investigate ‘Kepler Objects of Interest’ KOI’s. These are Exo planets suspects, where the Kepler space telescope has gathered some data but not enough to confirm the existence with confidence. In many cases Kepler will not do more work on those objects, opening up the opportunity for amateurs to contribute.
Do contact me if you would like to know more or you are an amateur astronomer yourself and would like to have a go yourself.
Exo Planet HD189733b
This Exo planet was discovered in October 2005 and is 13% larger than Jupiter and orbits its star every 2.2 days. It’s host star is located in the direction of the constellation Vulpecula, the Fox.
I obtained the data shown here during an imaging session on the night of April 30th-May 1st 2015. In the days leading up to the predicted transit I carried out tests to firstly locate the right star and to do exposure measurements. It is critical to get the exposures in the right zone, to ensure that throughout the actual observing run there is no under or over exposure. Also important is the number of exposures, so if they are a few seconds some time delay is required to get a sensible number of data points.
All photometry for our Exo planet work has so far been through the red filter, with red light being scattered the least by the atmosphere.
In the hours leading up to ingress (first point of transit contact) I did further exposures tests as the seeing conditions can be different on the night.
(In fact I was in Hawaii on holiday at the time so was operating my telescope in Spain from my balcony on a sunny Hawaiian afternoon. That’s what you call astronomy)
The exposure time was 1.75 seconds Red filter giving an ADU count of 32,000 +/- approx 7,000. This was monitored throughout the run and some minor adjustments made.
The exposure plus download time for each 16Mb image was 23 seconds and with a built in delay of 12 seconds between each image this gave a time for each data point of 35 seconds.
Having ensured the scope was pointing exactly at the star, focussed, set the guiding and done the last minute exposure tests, it was ready to run. The imaging started at 3;42cet about an hour before ingress and finished at 6 cet (just as it was getting light) which was about 40 minutes after the predicted egress.
I obtained about 400 data points, by far the best run to date.
Ben used his recently obtained software Pixinsight with an exo planet extension to do the photometry analysis, which can be seen opposite.
The transit time and depth concurs with published data. More analysis to follow.