How to Make a Light Curve for an Exoplanet Transit
This guide describes how to create a light curve for an exoplanet transit by measuring the brightness of the target star and a comparison star in several frames. You can do this with sample data available from the Faulkes Telescopes, or with data from your own observation if you have an account. After doing this activity you should be able to:
* Use SalsaJ to do photometry for an exoplanet transit
* Use a spreadsheet to create a light curve showing how the brightness of the target star changes over time
* Describe how the light curve shows that as the planet goes in front of the star it blocks some of the light
The Introduction to Photometry, Extrasolar Planets History and Detection, and Magnitude and Distance Measurement articles contain background information relevant to this project.
You will find that the text contains many links. Some will take you to a glossary definition, while others are links to more information about a topic you may want to explore further. Please use this guide in the way that makes most sense to you. You may want to read the entire guide first, then go back and follow links that interest you, or you may want to follow links as you go along. You can also click on the diagrams to see them a larger size.
Photometry of an Exoplanet Transit with SalsaJ
Download SalsaJ from the European Hands On Universe Website. (Until further notice, please download version 1.4, not version 2.0, which does not yet have full photometry features.)
Launch SalsaJ and the 
, or a spreadsheet such as Excel, OpenOffice Spreadsheet or Numbers.
Download and unzip sample data for one of the extrasolar planets below:
- Advanced
Use the screencast below to learn how to use SalsaJ and a spreadsheet to make a light curve for a transiting exoplanet:
Below are the main steps demonstrated by the screencast:
- Open the first FITS file in SalsaJ
- Change the brightness as needed to view the image
- Open the finder chart (a .jpg file in the folder with the sample transit data) and compare to figure out which star is the one with a transit
- In SalsaJ got to Analyze -> Photometry Settings and enter your chosen star and sky radii
- Enter the radii in your spreadsheet (you might need them later in case you have to redo any part of this)
- Go to your spreadsheet and enter the name of the FITS file (or some unique part of it) in the Image Identifier column
- In the FITS image, go to Image -> Show Info and look for the UTSTART time. Enter this time in your spreadsheet.
- Got to Analyze -> Photometry, then click on the star with a transit. Enter the intensity value in your spreadsheet under Target Intensity.
- Choose another bright star in the image (you might even want to do several separately and add extra columns to your spreadsheet for this) and click on it. Enter the intensity value in your spreasheet under Comparison Intensity.
- The spreadsheet divides the Target Intensity by the Comparison Intensity to adjust for any atmospheric brightening or dimming, and plots a point on the graph.
- Repeat steps 6-9 for each of the remaining transit images. (You will have to adjust the brightness for each one, but the photometry radii will stay the same)