HAT-P-67b: An Extremely Low Density Saturn Transiting an F-subgiant Confirmed via Doppler Tomography

May 2017 • 2017AJ....153..211Z

Authors • Zhou, G. • Bakos, G. Á. • Hartman, J. D. • Latham, D. W. • Torres, G. • Bhatti, W. • Penev, K. • Buchhave, L. • Kovács, G. • Bieryla, A. • Quinn, S. • Isaacson, H. • Fulton, B. J. • Falco, E. • Csubry, Z. • Everett, M. • Szklenar, T. • Esquerdo, G. • Berlind, P. • Calkins, M. L. • Béky, B. • Knox, R. P. • Hinz, P. • Horch, E. P. • Hirsch, L. • Howell, S. B. • Noyes, R. W. • Marcy, G. • de Val-Borro, M. • Lázár, J. • Papp, I. • Sári, P.

Abstract • We report the discovery of HAT-P-67b, which is a hot-Saturn transiting a rapidly rotating F-subgiant. HAT-P-67b has a radius of {R}_{{p}}={2.085}_-0.071^+0.096 {R}_{{J}}, and orbites a {M}_*={1.642}_-0.072^+0.155 {M}_⊙, {R}_*={2.546}_-0.084^+0.099 {R}_⊙ host star in a ∼4.81 day period orbit. We place an upper limit on the mass of the planet via radial velocity measurements to be {M}_{{p}}< 0.59 {M}_{{J}}, and a lower limit of > 0.056 {M}_{{J}} by limitations on Roche lobe overflow. Despite being a subgiant, the host star still exhibits relatively rapid rotation, with a projected rotational velocity of v\sin {I}_\star=35.8+/- 1.1 {km} {{{s}}}^-1, which makes it difficult to precisely determine the mass of the planet using radial velocities. We validated HAT-P-67b via two Doppler tomographic detections of the planetary transit, which eliminate potential eclipsing binary blend scenarios. The Doppler tomographic observations also confirm that HAT-P-67b has an orbit that is aligned to within 12°, in projection, with the spin of its host star. HAT-P-67b receives strong UV irradiation and is among one of the lowest density planets known, which makes it a good candidate for future UV transit observations in the search for an extended hydrogen exosphere.

Based on observations obtained with the Hungarian-made Automated Telescope Network. Based in part on observations made with the Keck-I telescope at Mauna Kea Observatory, HI (Keck time awarded through NASA programs N029Hr, N108Hr, N154Hr, and N130Hr; and NOAO programs A289Hr and A284Hr). Based in part on observations obtained with the Tillinghast Reflector 1.5 m telescope and the 1.2 m telescope, both of which are operated by the Smithsonian Astrophysical Observatory at the Fred Lawrence Whipple Observatory in Arizona. This work makes use of the Smithsonian Institution High Performance Cluster (SI/HPC). Based in part on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

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Benjamin Fulton

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