2 research outputs found
TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS and HARPS
A large sample of long-period giant planets has been discovered thanks to
long-term radial velocity surveys, but only a few dozen of these planets have a
precise radius measurement. Transiting gas giants are crucial targets for the
study of atmospheric composition across a wide range of equilibrium
temperatures and for shedding light on the formation and evolution of planetary
systems. Indeed, compared to hot Jupiters, the atmospheric properties and
orbital parameters of cooler gas giants are unaltered by intense stellar
irradiation and tidal effects. We identify long-period planets in the
Transiting Exoplanet Survey Satellite (TESS) data as duo-transit events. To
solve the orbital periods of TESS duo-transit candidates, we use the
CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability
period aliases in order to discard or confirm a transit event at a given
period. We also collect spectroscopic observations with CORALIE and HARPS in
order to confirm the planetary nature and measure the mass of the candidates.
We report the discovery of a warm transiting Neptune-mass planet orbiting
TOI-5678. After four non-detections corresponding to possible periods, CHEOPS
detected a transit event matching a unique period alias. Joint modeling reveals
that TOI-5678 hosts a 47.73 day period planet. TOI-5678 b has a mass of 20
(+-4) Me and a radius of 4.91 (+-0.08 Re) . Using interior structure modeling,
we find that TOI-5678 b is composed of a low-mass core surrounded by a large
H/He layer with a mass of 3.2 (+1.7, -1.3) Me. TOI-5678 b is part of a growing
sample of well-characterized transiting gas giants receiving moderate amounts
of stellar insolation (11 Se). Precise density measurement gives us insight
into their interior composition, and the objects orbiting bright stars are
suitable targets to study the atmospheric composition of cooler gas giants.Comment: 17 pages, 10 figures, accepted to A&