Using SalsaJ To Do Photometry For Extrasolar Planet Transits

You can study extrasolar planet transits using sample data sets, data from the LCOGT observations archive, or data from Agent Exoplanet.

The videos below are screencasts taking you through the steps you need to follow as you learn to use SalsaJ and do photometry. Before viewing the screencasts, you may wish to 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 download our lightcure plotter spreadsheet (you will need a spreadsheet application such as Excel, OpenOffice Spreadsheet or Numbers).

Download and unzip sample data for one of the extrasolar planets below:

How to choose a radius for photometry in SalsaJ:

 

How to do photometry with SalsaJ:

 

How to plot a light curve for an extrasolar planet transit:

 

Below are the main steps demonstrated by the screencast:

  1. Open the first FITS file in SalsaJ.
  2. Change the brightness as needed to view the image.
  3. 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.
  4. In SalsaJ got to Analyze -> Photometry Settings and enter your chosen star and sky radii.
  5. Enter the radii in your spreadsheet (you might need them later in case you have to redo any part of this.)
  6. Go to your spreadsheet and enter the name of the FITS file (or some unique part of it) in the Image Identifier column.
  7. In the FITS image, go to Image -> Show Info and look for the UTSTART time. Enter this time in your spreadsheet.
  8. Got to Analyze -> Photometry, then click on the star with a transit. Enter the intensity value in your spreadsheet under Target Intensity.
  9. 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.
  10. 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.
  11. 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.)
Activity time: 
45 minutes - 1 hour
Objectives: 

Open FITS files in SalsaJ.

Choose appropriate photometry and sky radii. 

Measure the intensity of a target star and comparison stars and enter them into a spreadsheet.

Plot a lightcurve graph showing intensity over time for the transit.