Variable Star and Exoplanet Section of Czech Astronomical Society

Computing exoplanets parameters from transit light curve

Using a simple geometric model, we can compute two parameters from a single light curve of exoplanet transit, R_p - planet radius and inclination angle i.

Planet radius can be directly computed from depth of the transit. Inclination angle can be computed from length of the transit along with catalogue parameters R_s - star's radius, a - semi major axis and orbital period P. For detailed description and equations see:
Parameters of transiting exoplanet system

Uncertainities of R_p and i values
- Uncertainity of planet radius is computed from errors of derived depth of the transit. The error is first added to the derived depth and than deducted. In such way, we obtain the resulted error bars of R_p.
- Uncertainity of inclination angle is computed twice.
A) Uncertainity is computed just from errors of derived length of transit and planet radius (R_s and a are fixed) - dashed lines in the picture.
B) Uncertainity is computed with uncertainities of catalogue values of R_s and a - grey area in the picture.
Errors are added / deducted to the equation (5) so that we obtain maximal error bars.
Please note, that errors of star's radius and semi major axis can be dominant source of resulted uncertainity of the inclination angle.