THE DETECTABILITY OF TRANSIT SIGNALS FROM A MICROLENSED SOURCE STAR WITH EUCLID

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Abstract

Since the middle of the 1990’s, surveys into exoplanets have started to blossom and the interst into this area has been increasing. There are several space missions with the main aim of detecting exoplanets and future missions are anticipated. Ground-based observatories also carry out surveys into exoplanets very actively. Upcoming microlensing survey such as ’KMTNet (Korea Micro-lensing Telescope Network)’ could contribute considerably by observing thousands stars in the Galactic bulge with a high observational frequency (Kim et al., 2010). In addition to this, one of the ESA’s upcoming space mission called ’Euclid’ is aslo expected to contribute to the area of exoplanet detection through microlensing technique despite the fact that Euclid’s main goal is to study dark energy. Advancements in detector technologies and analysis techniques will open up a new era of stuyding exoplanets by gravitational microlensing for example, assisting in making more informative ’exoplanet demography’ (Penny et al., 2013). Furthermore, transit surveys are a very active research, particularly with legacy missions such as ’Kepler’ and ’CoRoT’. Apart from this, ground-based surveys have been also active by such as ’MEarth’ and ’HATNet (Hungarian-made Automated Telescope)’.In this dissertation, the detectability of transit signals of exoplanets orbiting around a source star is investigated with Euclid’s photometry. The basic concept of this simulation is that when a source star, which is generally faint is magnified by microlensing effect, some transit signals of exoplanet orbiting around a source star can be detected. 9311 source stars were enerated based on the Besancon Galactic model and simulated. We also generated exoplanet properties such as mass, radius, period, host separation and etc based on a Keplerian orbit assuming that every source star has only one exoplanet. As a next step, we set several selection conditions in terms of signal-to-noise ratio (SNR), orbital period and period precision between generated period and fitted period. When it comes to the SNR selection condition, we set a threshold of 50, which corresponds to a 2% uncertainty. Orbital periodis also set as a maximum 10 days for the confirmation of transit signals from the observation duration (30 days) of our scenario. We also set a cutline for the period precision within 1%. More detailed information and procedures are described in the following sections. The main result is that we can achieve a 18% detectability with Euclid. This value may change when limb darkening and orbit eccentricity effects are considered. Furthermore, since only a single source star with one exoplanet orbiting was investigated in this disseration, there will be also some changes in the result if binary or multiple systems are considered.

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