Orbital period analyses of eclipsing binaries depend on the correctness of the observed mid-eclipse time determination (as well the reliability of its uncertainty estimation). To determine an orbital period, you must measure the mid-time of eclipse, the so called Time of Minimum (ToM). The majority of ToMs have been determined by means of the Kwee-van Woerden method.

For the analysis of period evolutions in Delta Scuti variable stars, researchers often also use the Kwee-van Woerden method, to determine either Time of Minima or Time of Maxima. These minima / maxima timings (moments of extrema) are used for the “O-C” studies of the period changes.

There are still other application domains where one needs to accurately define the time of minimum or maximum in (a part of) a light curve. Next to the Kwee-van Woerden method, Peranso offers a method based on polynomial fitting. We will describe both methods in this tutorial.

Using synthetic light curves

The light curves used in this tutorial are so called synthetic light curves. These are artificial light curves with 'pseudo-observations' having known statistical and variability properties. It will allow us to compare the correct ToM with the measured ToM for the above methods. We selected the pseudo-observations in such a way that no  data point represents the real ToM.