How to Analyze Your Exoplanet Observations

Whether you use your own telescope to observe an exoplanet transit or use someone else's observations, the next step is to turn your pictures of the night sky into a light curve so you can see the change in brightness when the exoplanet you're observing passes in front of its host star. Here's how to do that analysis:

What is Data Analysis?

Astronomers routinely make use of observations from both ground- and space-based telescopes. Often, these observations are in the form of pictures and need to be analyzed (also commonly called "reduced") in order to extract their scientific content. For transiting exoplanets, astronomers need to monitor changes in the observed brightness of the star as the planet passes in front of it. These graphs showing a star's change in brightness during planet transits are called "lightcurves".

What Should I Use to Analyze my Data?

Once you have observed an exoplanet transit with your own telescope or requested robotic telescope data of an exoplanet transit, the next step is to use a data reduction tool like EXOTIC to convert your image files into a transit lightcurve, which will measure the planet passing in front of and partially blocking its host star.

Exoplanet Watch's official (and free!) data reduction software is the EXOplanet Transit Interpretation Code (EXOTIC). Below, we provide some helpful instructions and links to use EXOTIC to create light curves from your own exoplanet transit observations.

How to Analyze Your Transiting Exoplanet Observation and Make a Light Curve Using EXOTIC

EXOTIC logo. Credit: Swetha Ganesh

Exoplanet Watch's EXOplanet Transit Interpretation Code (EXOTIC)

EXOTIC, the official data reduction pipeline of Exoplanet Watch, is a free Python3 package for reducing observations (raw FITS images) of transiting exoplanets into lightcurves. It can calibrate your data (i.e., with flats, darks, and biases) and then choose the ideal combination of comparision star, aperture, and sky annulus to extract a transit lightcurve. It then fits your observed transit with a model lightcurve to calculate the transit depth (which measures the size of the planet relative to its host star) and mid-transit time (which helps us more accurately calculate future transits).

EXOTIC can run on a Windows, Macintosh, or Linux/Unix computer. You can also use EXOTIC via the free Google Colab, which features cloud computing, many helpful plotting functions, and a simplified installation. However, if you are a user with many images or large images, we recommend running EXOTIC locally on your own computer.

Run the Google Colab Cloud version of EXOTIC

  • Features: does not require the user to install any software locally on their own computer.
  • Limitations: Requires user to upload their images to a free Gdrive account.
  • Recommendations: If you run out of space on your default Google/Gdrive account, you can sign up for a new, free account to use. Some users even make a new Google account for every new dataset to avoid running out of space.
  • There are now three versions of EXOTIC:
    • A Beginner Tutorial training module that walks you through the steps of how to turn telescope observations into light curves using sample data,
    • a Standard module for people who use data from MicroObservatory robotic telescopes (we can give you data to convert to a light curve), and
    • an Advanced module for people who use observations from their own telescope.
  • How to use EXOTIC on the Colab video (video captions/transcript coming soon)

OR Download EXOTIC from GitHub and Run EXOTIC Locally On Your Own Computer (for advanced participants. There are known issues with this software if using it on a Windows machine.)

  • Features: Images are read off of the user's hard drive -- nothing is uploaded to Gdrive. This method can be helpful for those with large filesizes, many files, or a slow internet connection.
  • Limitations: Requires user to install Python3 and multiple subpackages.
  • Installation Instructions for Windows. Mcintosh, and Linux/Unix computers

Alternatively, if you are already using other software to reduce your exoplanet transit observations, you can use any other reduction code that you would like -- as long as the data is in the correct format for uploading to the AAVSO Exoplanet Database.

If you're making observations of exoplanets with your own telescope, your pictures should be saved in the FITS format. Astronomers use a file format called FITS format. The header of a FITS file contains information about the telescope, its location, filters that were used, and other information about the conditions under which the observations were taken.

NOTE: Before you run EXOTIC for the first time, to contribute your own transiting exoplanet data to the AAVSO Exoplanet Section Database and Exoplanet Watch, you need to sign up for your own free AAVSO account so that we can give you credit for your work. You only need to do this step once, and on subsequent data sets, you will use the same AAVSO Observer Code, so keep track of your four-letter Observer Code for future reference. You don't need to be a paid member of the AAVSO in order to create an AAVSO account and upload your data. Despite the name, you don't need to be American to contribute to the American Association of Variable Star Observers. It's open to anyone and everyone. The Observer Code maintains anonymity on our Results page, while enabling scientists writing papers about exoplanets you studied to include you as a co-author.

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