HD 189733 Exo-planet Transit


HD 189733, also known as V452 Vulpecula (the Fox), has a Jupiter sized planet (HD 189733 b) whose orbital plane is aligned with us.  This means that it "transits" or crosses in front of the parent star causing a light reduction from the star of somewhere between 2% and 3%.  This reduction can be measured from here on earth and the planet is "detected".  (Actually taking a picture of this planet is not possible).  HD 189733 is 63 light years away and is a magnitude 7.7 star.  It is just 20 arc minutes East of M27 the Dumbbell Nebula.

The plot below is relative intensity from a blizzard of individual images over a three hour period on the night of 20/21 August at the 2009 Oregon Star Party.  The plot shows the light dip for the two hour transit event centered around 12:28 am.  The data drop out (gap) on the left was a pier flip problem and a mad scramble to untangle and re-point the scope.

The images were taken with the ST-8E camera at f/5 on the FSQ 106N .  They are full spectrum / clear filter  images (as detailed below).  Calibration and photometry (intensity analytics) were done in MaxIm DL.  Each data point in the chart above is also a moving average of 13 points.  This smoothed the data some.  A composite of all the images is below.  The brighter looking star in the middle is HD 1897330.  M27 can also be seen.

Image details are below.  The center 1/4 subframe was chosen to speed up downloads and cram more images into the session.  Also, the auto-guider was not used.  I did not want to have small image shifts during the exposures.  Instead, I plate solved each image for its sky location and fed that back to the scope in-between images.  Basically, the individual images each "guided" the session.


Exposure Count Binning Subframe
Clear 10 sec 376 1x1 center 1/4