phot2lc Screenshot

Throughout my time as an observational astronomy PhD student, I have obtained and reduced enough data to fill up my computer hard drive several times over. My data typically come in the form of time-series photometry, meaning that when I’m at the telescope I will observe a single star for several hours at a time, taking one image after another in 5-10 second intervals, often resulting in hundreds or even thousands of images per night (about 1-2 GB). Ultimately, these images will need to be converted into light curves, which are the final data product indicating a star’s brightness versus time. To get from raw images to light curves, the following steps are performed:

  • Image Calibrations (Dark, Flat, and Bias corrections)
  • Circular Aperture Photometry
  • Light Curve Extraction

When dealing with alot of data, large amounts of time can be saved if the software tools used for data reduction are designed to increase efficiency. phot2lc was born from the desire to have a more efficient tool for light curve extraction from time-series photometry, especially in the event that light curves from multiple aperture sizes need to be analyzed to determine the optimal size.

phot2lc is a pure-Python interactive program for light curve extraction inspired largely by WQED (Thompson & Mullally 2009, 2013). While not nearly as extensive in its scope as WQED, phot2lc has several key features which make it a much more efficient and user-friendly tool for light curve extraction. The first such feature is its ease of installation. phot2lc is a Python package and can be installed with:

pip install phot2lc

Detailed documentation for phot2lc can be found at

List of Features

  • Standard Light Curve Manipulation Tools:
    • Delete/Add single points
    • Delete points inside and outside a drawn box
    • Divide by a polynomial of chosen order
    • Delete outliers with a sigma clipping routine
    • Comparison star selection
  • Analyzes photometry for all apertures sizes at once
  • Automated determination of optimal aperture size
  • Automated determination of optimal comparison star combination
  • Barycentric time corrections with Astropy accounting for:
    • Object RA and Dec Coordinates
    • Observatory Location
    • Leap Seconds
  • Additional tools for post-processing:
    • weldlc for combining light curves
    • quicklook for quick analysis of light curves and their periodograms
  • Automatically loads previous changes made to a light curve (i.e. same deleted points, polynomial, and comparison stars) when phot2lc is re-run for an object.