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

Espinoza, N., Brahm, R., Henning, T., Jordan, A., Dorn, C., Rojas, F., Sarkis, P., Kossakowski, D., Schlecker, M.,Díaz, M. R., Jenkis, J. S., Aguilera Gómez, C.,Jenkis, J. M., Twicken, J. D., Collins, K. A.,Lissauer, J., Armstrong, D. J., Adibekyan, V., Barrado, D., Barros, S. C. C., Battley, M., Bayliss, D., Bouchy, F., Bryant, M., Cooke, B. F., Demangeon, O. D. S., Dumusque, X., Figueira, P., Giles, H., Lillo Box, J., Lovis, C., Nielsen, L. D., Pepe, F., Pollaco, D., Santos, N. C., Sousa, S. G., Udry, S., Wheatley, P. J., Turner, O., Marmier, M., Segransan, D., Ricker, G., Latham, D., Seager, S., Winn, J. N., Kielkopf, J. F., Hart, R., Wingham, G., Jensesn, E. L. N., Helminiak, K. G., Tokovinin, A., Briceno, C., Ziegler, C., Law, N. M., Mann, A. W., Daylan, T., Doty, J. P. Guerrero, N., Boyd, P. Crossfield, I., Morris, R. L., Henze, C. E., Chacon, A. D. (2020). HD 213885b: a transiting 1-d-period super-Earth with an Earth-like composition around a bright (V=7.9) star unveiled by TESS. Monthly Notices of the Royal Astronomical Society 491, 2, 2982-2999 DOI: 10.1093/mnras/stz3150

We report the discovery of the 1.008-d, ultrashort period (USP) super-EarthHD213885b (TOI141b) 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 +/- 0.6M. 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, whoseminimum mass of 19.9 +/- 1.4M. 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.

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