* Astronomy

Title: HAT-P-67b: An Extremely Low Density Saturn Transiting an F-Subgiant Confirmed via Doppler Tomography
Author: G. Zhou, G. A. Bakos, J. D. Hartman, D. W. Latham, G. Torres, W. Bhatti, K. Penev, L. Buchhave, G. Kovács, A. Bieryla, S. Quinn, H. Isaacson, B. J. Fulton, E. Falco, Z. Csubry, M. Everett, T. Szklenar, G. Esquerdo, P. Berlind, M. L. Calkins, B. Béky, R. P. Knox, P. Hinz, E. P. Horch, L. Hirsch, S. B. Howell, R. W. Noyes, G. Marcy, M. de Val-Borro, J. Lázár, I. Papp, P. Sári

We report the discovery of HAT-P-67b, a hot-Saturn transiting a rapidly rotating F-subgiant. HAT-P-67b has a radius of Rp = 2.085 -0.071/+0.096 RJ, orbiting a M* = 1.642 -0.072/+0.155 Msun, R* = 2.546 -0.084/+0.099 Rsun 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 Mp < 0.59 MJ, and lower limit of > 0.056 MJ 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* = 35.8 ± 1.1 km/s, making 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 eliminated potential eclipsing binary blend scenarios. The Doppler tomographic observations also confirmed that HAT-P-67b has an orbit that is aligned, in projection, with the spin of its host star. Due to the large radius and low mass of HAT-P-67b, it is amongst the lowest density gas giants known.

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