Imprints of Stellar Activity in Exoplanetary Transit Light Curves

Bhattacharya, Richik (2025) Imprints of Stellar Activity in Exoplanetary Transit Light Curves. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Richik Bhattacharya (20MS168)) 20MS168_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (4MB)

Abstract

exoplanets. In the past Kepler had discovered around 3247 exoplanets while K2 had discovered about 427 exoplanets. Ongoing missions like TESS is expected to find at least 3000 exoplanets and the very recent JWST has started bringing more data. This has created a recent surge in exoplanetary studies. Detection of exoplanets as well as atmospheric characterization is done via transit photometry. The transit data also include information about the stellar background occulted by the planet in addition to the information regarding the exoplanet’s atmosphere. Although substantial work has been done to characterize the atmosphere of exoplanets, the role of the stellar background (spots and faculae) on the transit light curve remains largely unexplored and difficult to disentangle. In this thesis, we attempt to do the following: a) Study the interplay of stellar activity, stellar rotational modulation and their signatures on transit light curves b) We also try to compare photometric rotational variation with transit residuals to figure out which of the two is a better technique for inferring information about stellar activity. Conversely, this also addresses the question of which of the two (among rotational modulation and transit residual) is a better signature of stellar activity. To achieve this, we perform numerical simulations with synthetic star spot inputs and modeled exoplanetary transit profiles using a stellar surface flux transport model. We explore various scenarios such as diverse stellar rotation rates, different transit impact parameters. Our simulations include the physics of stellar spot and faculae contributions. We find that transit residuals is a better indicator of stellar activity as compared to rotational modulation but only for those cases where the transit does not happen along the primary activity belt v (latitudes) of the star. For transits along the activity belt, we obtain a very weak correlation of transit residuals with stellar activity parameters. Further exploration building upon this research may help generate better constraints on stellar activity in exoplanetary transit residuals.

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