About

The transit method has been one of the most useful and prominent methods of exoplanet detection. The basic principle behind transit measurements relies on the passage of a planet in front of its parent star. This causes a change in the observed flux, thus pointing towards the possible existence of a planet. To measure such changes, transit photometry is used. In this work, a procedure for extracting planetary transit parameters using observations of the parent star have been outlined and followed, which finally returns a transit curve and utilizing it, the required planetary parameters. We reduce photometric observations of a planetary transit to measure the flux drop as the exoplanet passes in front of its host star. The results may be improved with more measurements but suffice to demonstrate transit photometry herein. This project uses a sample of 42 frames of observations made on 31 October 2017 with EulerCam, the CCD camera of at the 1.2m Euler telescope at La Silla observatory (Chile). Photometric extractions of the flux of star WASP-52, along with 3 other stars (reference stars) is done defining apertures. These measurements are then manipulated – first by dividing the target star flux by reference star flux and second by normalizing this relative flux – to best visualize and analyze the planetary transit. The results are interpreted and used for determination of planetary parameters.

Results

The star observed is WASP-52, with an exoplanet transiting at a period of ~1.75 days. The observational data comes from EulerCam, the CCD camera at the 1.2m Euler telescope at the La Silla observatory (Chile). From the performed photometry, it is found that the star (with some stellar parameters known and taken from different measurements) WASP-52 has a transiting exoplanet orbiting on a semi major axis of 0.03 AU, inclined at 86.13°. Multiple reference stars used for photometry also indicate that better results are obtained when the difference in apparent magnitudes of target star and reference star is lower. The analysis also suggests that even fundamental, short duration observations of transits are valuable in exoplanet findings. While single-transit observations cannot provide information about planet periods, combined with data from other observations, such data holds the potential to give fundamental planetary parameters like planet radius, inclination and semi-major axis of orbit, planet density and impact parameter. Considering the calculation, the visually best transit curve also returns planetary parameters closest to the original, giving a planetary radius of 1.243 R Jupiter . This value is correct to one decimal place, the difference from the original value being ~0.03 R Jupiter . The semi-major axis being just a function of period and stellar mass, doesn’t vary with our specification of reference stars as both values are external inputs. The impact parameter, the planet density and the orbital inclination experience considerable variation with selection of reference star. The impact parameter seems very sensitive to shape of transit, as also pointed out in Seager and Mall´en-Ornelas (2002). Analysis of the physical quantities derived complements the bias we say the current ground-based transit searches have - sensitivity towards close-in, large planets. The planet characteristics, specifically the radius and size of orbit, pave way for the possibility of the exoplanet being a Hot Jupiter. The same inference is a stated result in Hébrard et al., 2013. Overall, this analysis provides good insights into transit photometry and related calculations. Improvements in such an analysis can be made in a number of ways. Incorporating limb darkening effects, error modelling, transit curve fitting and multiple-transit observations may lead to more accurate determination of parameters. Furthermore, transit spectroscopy can give insights into the exoplanet’s atmosphere.