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HD 213885b: a transiting 1-d-period super-Earth with an Earth-like composition around a bright (V = 7.9) star unveiled by TESS

N. Espinoza, R. Brahm, T. Henning, A. Jordán, C. Dorn, F. Rojas, P. Sarkis, D. Kossakowski, M. Schlecker, M. R. Díaz, J. S. Jenkins, C. Aguilera-Gomez, J. M. Jenkins, J. D. Twicken, K. A. Collins, J. J. Lissauer, D. J. Armstrong, V. Zh. Adibekyan, D. Barrado, S. C. C. Barros, M. Battley, D. Bayliss, F. Bouchy, E. M. Bryant, B. F. Cooke, O. Demangeon, X. Dumusque, P. Figueira, H. A. C. Giles, J. Lillo-Box, C. Lovis, L. D. Nielsen, F. Pepe, D. Pollacco, N. C. Santos, S. G. Sousa, S. Udry, P. J. Wheatley, O. Turner, M. Marmier, D. Ségransan, G. R. Ricker, D. W. Latham, S. Seager, J. N. Winn, J. F. Kielkopf, R. Hart, G. Wingham, E. L. N. Jensen, K. G. Hełminiak, A. Tokovinin, C. Briceño, C. Ziegler, N. M. Law, A. W. Mann, T. Daylan, J. P. Doty, N. Guerrero, P. Boyd, I. J. M. Crossfield, R. L. Morris, C. E. Henze, A. Chacón

Abstract
We report the discovery of the 1.008-d, ultrashort period (USP) super-Earth HD 213885b (TOI-141b) orbiting the bright (V = 7.9) star HD 213885 (TOI-141, TIC 403224672), detected using photometry from the recently launched TESS mission. Using FEROS, HARPS, and CORALIE radial velocities, we measure a precise mass of 8.8 ± 0.6 M⊕ for this 1.74 ± 0.05 R exoplanet, which provides enough information to constrain its bulk composition – similar to Earth’s but enriched in iron. The radius, mass, and stellar irradiation of HD 213885b are, given our data, very similar to 55 Cancri e, making this exoplanet a good target to perform comparative exoplanetology of short period, highly irradiated super-Earths. Our precise radial velocities reveal an additional 4.78-d signal which we interpret as arising from a second, non-transiting planet in the system, HD 213885c, whose minimum mass of 19.9 ± 1.4 M makes it consistent with being a Neptune-mass exoplanet. The HD 213885 system is very interesting from the perspective of future atmospheric characterization, being the second brightest star to host an USP transiting super-Earth (with the brightest star being, in fact, 55 Cancri). Prospects for characterization with present and future observatories are discussed.

Keywords
techniques: photometric; techniques: radial velocities; planets and satellites: detection; planets and satellites: fundamental parameters; planets and satellites: individual: TOI-141; TIC 403224672; HD213885; Astrophysics - Earth and Planetary Astrophysic

Monthly Notices of the Royal Astronomical Society
Volume 491, Issue 2, Page 2982
2020 January

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia