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Two cool TESS giant planets in circular orbits

Presentation #102.05 in the session Transiting Planets and TTVs.

Published onApr 03, 2024
Two cool TESS giant planets in circular orbits

We present the discovery of HD 115587 b, a planet with a 0.7 MJ mass, a 0.49 RJ radius, and a circular 372-day orbit; and TOI 429, a planet with a 0.8 MJ mass, a 0.8 RJ radius, and a circular 338-day orbit. Both planets showed just one transit in TESS observations, but radial velocity follow-up with APF, HARPS, FEROS, CORALIE and Magellan-PFS revealed their mass and period. The periods were initially measured with relatively low precision due to the availability of just one transit. In the case of TOI 429, we have also carried out multiple photometric follow-up campaigns which ruled out ranges of possible periods, and ultimately observed a new transit with the Canadian NEOSSat microsatellite, tightly constraining the planet’s period and thus facilitating future transit observations. In addition to being prized targets for characterization of their atmospheres, orbital alignment and searches for additional planets, these two systems also highlight the ability to discover transiting planets with periods much longer than the duration of observations. Intriguingly, both planets have circular or near-circular orbits, suggesting that they may be probing parameter space beyond the typical warm Jupiter regime. Indeed, RV surveys indicate that giant planets with periods beyond 200 days are more likely to have circular orbits when compared to warm Jupiters. As such, HD 115587 b and TOI 429b may be among the first known transiting giant planets to probe Solar System-like orbits.

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