WASP-3 is a 10.7 magnitude star 3 degrees south of Vega in Lyra. WASP stands for Wide Angle Search for Planets. It consists of two robotic observatories in Spain and South Africa:

https://en.wikipedia.org/wiki/Wide_Angle_Search_for_Planets

Exoplanet “b” was discovered in 2007. It is a Jupiter-like planet 1.3 times the size of Jupiter. It revolves around WASP-3 every 1.846835 days. The duration of the transit is 137 minutes and its depth is 0.0123 magnitudes.

This is my second exoplanet, the first being HAT-P-5 b. Here is a write-up on it:

https://u235-varstar.now.sh/gallery/hat-p-5-b

You will notice that there is a lot of uncertainty in the data, nevertheless AstroImageJ was able to perform a transit model fit to my data.

Following that first experience I wanted to see what I could do to increase accuracy. Dr. Robin Glover suggested de-focusing as a technique to effectively turn my $400 camera into a $4000 camera.

Tonight I was not able to capture the entire transit from beginning to end but I did capture some high quality data for the second half. I de-focused as much as I could but there was a nearby 13th magnitude star only 18 arc-seconds away. Thankfully I set the exposure right, just below 55,000 ADU which is where my CCD begins to go non-linear.

Here are the results. I am very pleased with it:

The next step would be to work out the relationship between three variables: Star magnitude, Magnitude error, and Aperture.

• Aperture is equal to the amount of de-focus needed to achieve a certain star disc radius.
• Magnitude error (the 3rd column in the spreadsheet) should be no greater than half the depth of transit, preferably smaller.

It should be possible to work this out mathematically but I think I will take the empirical approach to see how the data points cluster and then fit a curve to it.

The goal is to achieve consistent results instead of guessing. It’s OK to rely on experience but it would be great to have a heads-up in the planning stage to determine if a target is within the abilities of my equipment. For example, I can tell you that there is no way my kit could handle a 16th magnitude star with a transit depth of 0.005 magnitudes. It’s not going to happen but there are other scenarios where I can pull it off. Let’s say that the star is 8th magnitude then I know I can detect it just using the experience I’ve accumulated thus far. That’s fine but I want a more rigorous approach.