HD 56414 b: A Warm Neptune Transiting an A-type Star
Published in The Astrophysical Journal Letters, 2022
We report the discovery in TESS data and validation of HD 56414 b (a.k.a. TOI-1228 b), a Neptune-size (R_p = 3.71 ± 0.20 R_Earth) planet with a 29 day orbital period transiting a young (age = 420 ± 140 Myr) A-type star in the TESS southern continuous-viewing zone. HD 56414 is one of the hottest stars (T_eff = 8500 ± 150 K) to host a known sub-Jovian planet. HD 56414 b lies on the boundary of the hot Neptune desert in the planet radius-bolometric insolation flux space, suggesting that the planet may be experiencing mass loss. To explore this, we apply a photoevaporation model that incorporates the high near-ultraviolet continuum emission of A-type stars. We find that the planet can retain most of its atmosphere over the typical 1 Gyr main-sequence lifetime of an A-type star if its mass is ≥ 8 M_Earth. Our model also predicts that close-in Neptune-size planets with masses < 14 M_Earth are susceptible to total atmospheric stripping over 1 Gyr, hinting that the hot Neptune desert, which has been previously observed around FGKM-type stars, likely extends to A-type stars.
Recommended citation: Giacalone, S., Dressing, C. D., Garcia Munoz, A., et al., 2019, The Astrophysical Journal Letters, 935, L10
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