Photometric searches for exoplanets and variability in star clusters

This thesis is focused on the photometric analysis of stellar light curves (LCs), to search for variable stars and transiting extrasolar planets. In particular, this study is carried out on crowded fields which include open clusters (OCs). The context of my work is the photometric preparatory survey “The Asiago Pathfinder for HARPS-N” (APHN; PI: Bedin) aimed at characterising OCs (i.e. M44, NGC752, M35, NGC2158 and M67) to be observed with the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N), mounted at the Telescopio Nazionale Galileo (TNG). The APHN survey was also recently extended to an additional sample of OCs which were chosen as targets for the Kepler extended mission K2 (Howell et al. 2014), in view of creating astrophotometric master input catalogues for high-precision photometry of Kepler and K2 data, following the method developed by (Libralato et al. 2015a). We also analysed data coming from other ground-based facilities, such as the SuperWASP or the STELLA1 Telescope. Searches for transiting exoplanets within OCs, while challenging (van Saders & Gaudi 2011), are particularly useful to constrain the properties of both the host star and planet, and to unveil the planetary formation and evolution mechanisms (Janes 1996; Fischer & Valenti 2005). The first part of the thesis reviews the different photometric techniques so far developed and present in the literature to search for exoplanets and, in general, for stellar variability studies (chapter 1). A short review of the principal ground and space-based projects is also given at the end of this chapter. Chapter 2 describes the origin of systematics errors (“red noise”) and gives a description of the methods developed to correct the LCs before the search for variability. A description of the different type of stellar variability and of the algorithms used to search for periodical signals is given in chapter 3. My original analysis of the OCs data is described in the last four chapters, starting from M44 in chapter 4. There, after a description of the observational setup, I discuss the detrending algorithms, the procedure to detect periodic signal, and my results in terms of newly discovered variables, including a study of the gyrochronological period versus colour relation. The following chapters are organised in a similar way, but covering NGC752 (chapter 5), M35 & NGC2158 (chapter 6) and M67 (chapter 7), respectively.