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

Creators: Zhou, G.; Fulton, B. J.

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^(+0.096)_(-0.071) R_J, and orbites a M* = 1.642^(+0.155)_(-0.072) M⊙, R* = 2.546^(+0.099)_(-0.084) 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 ν sin I⋆ = 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.

Additional Information

© 2017 The American Astronomical Society. Received 2017 January 31; revised 2017 February 19; accepted 2017 March 2; published 2017 April 14. 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. We thank the referee for their insightful contributions to this manuscript. HATNet operations have been funded by NASA grants NNG04GN74G and NNX13AJ15G. The follow-up of HATNet targets has been partially supported through NSF grant AST-1108686. G.Á.B., Z.C., and K.P. acknowledge partial support from NASA grant NNX09AB29G. J.H. acknowledges support from NASA grant NNX14AE87G. K.P. acknowledges support from NASA grant NNX13AQ62G. We acknowledge partial support also from the Kepler Mission under NASA Cooperative Agreement NCC2-1390 (DWL, PI). Data presented in this paper are based on observations obtained at the HAT station at the Submillimeter Array of SAO and the HAT station at the Fred Lawrence Whipple Observatory of SAO. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Data presented herein were obtained at the WIYN Observatory from telescope time allocated to NN-EXPLORE through the scientific partnership of the National Aeronautics and Space Administration, the National Science Foundation, and the National Optical Astronomy Observatory. This work was supported by a NASA WIYN PI Data Award, administered by the NASA Exoplanet Science Institute. We acknowledge of J.A. Johnson in supporting the KECK-HIRES observations. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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