Confirming long-period transiting exoplanets with TESS and CHEOPS. The case of HD 22946 d

Abstract

Due to the limited observing duration of the Transiting Exoplanet Survey Satellite (TESS) primary mission, which observed the majority of the near-ecliptic sectors for only 27 days, planets on long periods produce only single transits. However, thanks to its extended mission, TESS re-observed the same fields 2 years later, and in many cases was able to re-detect a second transit. These 'duotransit' cases require follow-up in order to uncover the true orbital period due to the gap, which causes a set of aliases. The Characterising Exoplanet Satellite (CHEOPS) space observatory can be used to follow-up duotransit targets and to determine their true orbital periods and other characteristics. We investigated the HD 22946 planetary system with a similar aim. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d to be 47.42489 ± 0.00011 d, and derived precise radii of the planets in the system. Planet d, as a warm sub-Neptune, is very interesting because there are only a few similar confirmed exoplanets to date.