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XO-7 b: A Transiting Hot Jupiter with a Massive Companion on a Wide Orbit

N. Crouzet, B. F. Healy, G. Hébrard, P. R. McCullough, D. Long, P. Montañés Rodríguez, I. Ribas, F. Vilardell, E. Herrero, E. Garcia-Melendo, M. Conjat, J. Foote, J. Garlitz, P. Vo, N. C. Santos, J. de Bruijne, H. P. Osborn, S. Dalal, L. D. Nielsen

Abstract
Transiting planets orbiting bright stars are the most favorable targets for follow-up and characterization. We report the discovery of the transiting hot Jupiter XO-7 b and of a second, massive companion on a wide orbit around a circumpolar, bright, and metal-rich G0 dwarf (V = 10.52, Teff = 6250  ± 100 K,  [Fe/H] = 0.432 ± 0.057 dex). We conducted photometric and radial velocity follow-up with a team of amateur and professional astronomers. XO-7 b has a period of 2.8641424 ± 0.0000043 days, a mass of 0.709 ± 0.034 MJ, a radius of 1.373 ± 0.026 RJ, a density of 0.340 ± 0.027 g cm-3, and an equilibrium temperature of 1743 ± 23 K. Its large atmospheric scale height and the brightness of the host star make it well suited to atmospheric characterization. The wide-orbit companion is detected as a linear trend in radial velocities with an amplitude of ~ 100 m s-1 over two years, yielding a minimum mass of 4 MJ it could be a planet, a brown dwarf, or a low-mass star. The hot Jupiter orbital parameters and the presence of the wide-orbit companion point toward a high-eccentricity migration for the hot Jupiter. Overall, this system will be valuable to understand the atmospheric properties and migration mechanisms of hot Jupiters and will help constrain the formation and evolution models of gas giant exoplanets.

Keywords
Exoplanet astronomy; Exoplanets; Extrasolar gas giants; Hot Jupiters; Transits; Transit photometry; Transit instruments; Exoplanet systems; High resolution spectroscopy; Surveys; Visible astronomy; Radial velocity; Astrophysics - Earth and Planetary Astro

The Astronomical Journal
Volume 159, Number 2
2020 February

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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