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

Abstract

We report the discovery in TESS data and validation of HD 56414 b (a.k.a. TOI-1228 b), a Neptune-size ($R_{\mathrm{p}}=3.71\pm 0.20R_{\oplus }$) planet with a 29-day orbital period transiting a young (Age = $420\pm 140$ Myr) A-type star in the TESS southern continuous viewing zone. HD 56414 is one of the hottest stars ($T_{\mathrm{eff}}=8500\pm 150\mathrm{K}$) to host a known sub-Jovian planet. HD 56414 b lies on the boundary of the hot Neptune desert in 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 $\ge 8M_{\oplus }$. Our model also predicts that close-in Neptune-size planets with masses $<14M_{\oplus }$ 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.

12 pages, 4 figures, 1 table

References in corpus (8)

• The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics From 10-100 AU
• Accurate, Empirical Radii and Masses of Planets and their Host Stars with Gaia Parallaxes
• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• exoplanet: Gradient-based probabilistic inference for exoplanet data & other astronomical time series
• Eclipsing Binary Stars as Benchmarks for Trigonometric Parallaxes in the Gaia Era
• Empirical, Accurate Masses and Radii of Single Stars with TESS and Gaia
• Rapid escape of ultra-hot exoplanet atmospheres driven by Hydrogen Balmer absorption

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• The GAPS Programme at TNG. LXV. Precise density measurement of TOI-1430 b, a young planet with an evaporating atmosphere