HD 56414 b: A Warm Neptune Transiting an A-type Star

Steven Giacalone , Courtney D. Dressing , A. García Muñoz (1) , Matthew J. Hooton , Keivan G. Stassun , Samuel N. Quinn , George Zhou , Carl Ziegler , Roland Vanderspek , David W. Latham , S. Seager , Joshua N. Winn , Jon M. Jenkins , César Briceño , Chelsea X. Huang , David R. Rodriguez , Avi Shporer , Andrew W. Mann , David Watanabe , Bill Wohler

1 AIM (UMR_7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation

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 _⊕) 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 _⊕. Our model also predicts that close-in Neptune-size planets with masses <14 M _⊕ 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.

Mots clés: Exoplanet astronomy; Exoplanet systems; Exoplanet evolution; Transits

Domaines: Planète et Univers [physics]; Astrophysique [astro-ph]

Steven Giacalone, Courtney D. Dressing, A. García Muñoz, Matthew J. Hooton, Keivan G. Stassun, et al.. HD 56414 b: A Warm Neptune Transiting an A-type Star. The Astrophysical journal letters, 2022, 935, ⟨10.3847/2041-8213/ac80f4⟩. ⟨insu-03846754⟩