Exoplanets are now discovered on a daily basis thanks to many astronomical surveys. These surveys require additional follow-up observations for validation, for joint observations at different wavelenghts and for a precise and regular determination of the transit ephemerides. This need will become even more important with the forthcoming launch of JWST. In this domain, the potential of robotic medium size (30-80 cm) telescopes has been demonstrated by telescopes such as TRAPPIST in Chile and ASTEP in Antarctica. In 2021 only, ASTEP successfully detected 66 transiting planetary systems, leading to the confirmation of many of these systems. In particular, ASTEP has proven its ability to detect small planets (transit depth of 0.06%), very long period systems (a planet with a 139 days period, a triple system with an outer companion with a 235 days orbital period) and generally systems which are extremely difficult to observe from other latitudes (e.g. a 12 hour long planetary transit).
With a set of two new highly sensitive cameras to be installed for the 2022 observation campaign thanks to the funding of the University of Birmingham and of ESA, ASTEP+ is a major improvement of ASTEP, combining a higher efficiency and simultaneous observations in two colors. The improvement will be followed by the acquisition of a new direct-drive mount able to greatly enhance the precision and reliability of the observations.
We propose to pursue the operations of ASTEP+ in 2023 and beyond. ASTEP+ will continue the highly successful follow-up of TESS transiting planet candidates, focusing particularly on transiting planets on long orbital periods: while these planets are challenging to discover and validate, they represent choice targets for atmospheric characterization with the future JWST and ARIEL telescopes. ASTEP+ will also monitor known transiting exoplanets in order to obtain precise ephemerides for observations with larger facilities. Finally, the new mount will allow ASTEP+ to expand its scientific goals by including, in particular, the follow-up of the optical counterparts to gravitational wave events.