Two Validated Planets and 179 Candidates From a TESS Faint Star Transit Search in the ULTRASAT Fields

Abstract

The TESS mission is designed to survey the entire sky to find planets most amenable to follow-up observations, and transit searches have therefore focused specifically on bright targets. Faint stars ($T_{mag}>13.5$) have not been systematically searched for planets, despite TESS having the sensitivity necessary to do so, therefore representing a promising avenue for increasing TESS's scientific yield. We utilized TESS's sensitivity for faint stars in particular to find more planets for joint optical-UV studies of exoplanet transits. Observing transits in both UV and optical gives insight into exoplanet atmosphere composition and evolution and remains relatively unexplored due to the lack of UV-capable instruments. ULTRASAT is an upcoming UV space telescope that will perform a high cadence survey suitable for observing exoplanet transits. To increase the sample size of planets capable of observations with ULTRASAT, we performed a transit search of faint stars down to $T_{mag}=16$ in the ULTRASAT high cadence survey fields using TESS light curves optimized for faint stars. Our search recovered 262 planet candidates, of which 181 are new to this work. We also statistically validated 2 of those candidates as bona fide planets. Finally, we estimated the ULTRASAT SNR of both new and existing planet candidates, and found that 113 targets will be detectable with ULTRASAT, which would facilitate the largest study of transiting planets in the visible and UV. This work demonstrates the power of TESS to detect exoplanets around faint stars and provides a catalog of well-vetted transiting planet candidates to observe with ULTRASAT.