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Discovery of a young low-mass brown dwarf transiting a fast-rotating F-type star by the Galactic Plane eXoplanet (GPX) survey

P. Benni, A. Burdanov, V. Krushinsky, A. Bonfanti, G. Hébrard, J.-M. Almenara, S. Dalal, O. Demangeon, M. Tsantaki, J. Pepper, K. G. Stassun, A. Vanderburg, A. Belinski, F. Kashaev, K. Barkaoui, T. Kim, W. Kang, K. Antonyuk, V. V. Dyachenko, D. A. Rastegaev, A. Beskakotov, A. A. Mitrofanova, F. J. Pozuelos, E. D. Kuznetsov, A. Popov, F. Kiefer, P. A. Wilson, G. R. Ricker, R. K. Vanderspek, D. W. Latham, S. Seager, J. M. Jenkins, E. Sokov, I. Sokova, A. Marchini, R. Papini, F. Salvaggio, M. Banfi, Ö. Baştürk, Ş. Torun, S. Yalçınkaya, K. Ivanov, G. Valyavin, E. Jehin, M. Gillon, E. Pak¨tienė, V.-P. Hentunen, S. Shadick, M. Bretton, A. Wünsche, J. Garlitz, Y. Jongen, D. Molina, E. Girardin, F. Grau Horta, R. Naves, Z. Benkhaldoun, M. D. Joner, M. Spencer, A. Bieryla, D. J. Stevens, E. L. N. Jensen, K. A. Collins, D. Charbonneau, E. V. Quintana, S. E. Mullally, C. E. Henze

Abstract
We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of 19.7 ± 1.6 MJup and a radius of 1.47 ± 0.10 RJup, the first substellar object discovered by the Galactic Plane eXoplanet (GPX) survey. The brown dwarf transits a moderately bright (V = 12.3 mag) fast-rotating F-type star with a projected rotational velocity v sin i = 40 ± 10 km s−1. We use the isochrone placement algorithm to characterize the host star, which has effective temperature 7000 ± 200 K, mass 1.68 ± 0.10 M⁠, radius 1.56 ± 0.10 R⁠, and approximate age 0.27+0.09−0.15 Gyr. GPX-1 b has an orbital period of ∼1.75 d and a transit depth of 0.90 ± 0.03  per cent. We describe the GPX transit detection observations, subsequent photometric and speckle-interferometric follow-up observations, and SOPHIE spectroscopic measurements, which allowed us to establish the presence of a substellar object around the host star. GPX-1 was observed at 30-min integrations by TESS in Sector 18, but the data are affected by blending with a 3.4 mag brighter star 42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known to date, with a mass close to the theoretical brown dwarf/gas giant planet mass transition boundary. Since GPX-1 is a moderately bright and fast-rotating star, it can be followed-up by the means of the Doppler tomography.

Keywords
stars: brown dwarfs, stars: individual: GPX-1, stars: rotation, surveys: Astronomical Data bases, Galaxy: disc

Monthly Notices of the Royal Astronomical Society
Volume 505, Issue 4, Page 4956
2021 August

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