Natalia Rektsini

Cold Distant Worlds: A New Era of microlensing observations with ROMAN and EUCLID

Gravitational microlensing relies on the chance alignment of two or more stars in our galaxy. Over 200 planets have been found so far using this technique, in addition to several free-floating planet candidates, offering a small but diverse variety of planetary systems. In 2026 microlensing will enter a new observational era with the launching of the Nancy Grace Roman Space Telescope, the first space mission to conduct a microlensing survey, promising to increase the detection number by a factor of ten. One of the limiting factors of microlensing planet searches is to obtain accurate mass measurements. An approach to break this limit is to use constraints from high angular resolution follow-up observations (with KECK and HST until now) to measure the source-lens relative proper motions and flux ratios. I will present results from follow-up AO observations of microlensing events, discussing various types of planetary systems, located in different corners of our galaxy. Finally, I will discuss the importance of a EUCLID and ROMAN collaboration. Using simulated early EUCLID images of a star field containing 403 microlensing events that ROMAN will observe, I will explain the complementarity of the two missions. I will show how EUCLID precursor observations of the ROMAN fields will maximise the number of source-lens resolved images, offering precise mass and distance measurements of these microlensing events, offering additional constraints in our understanding of cold and warm planet demographics and planetary formation theories.