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

• Main 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., Val-Borro, M. de, Lázár, J., Papp, I., Sári, P.
• Other Authors: Univ Arizona, Steward Observ
• Language: en
• Published: IOP PUBLISHING LTD 2017
• Subjects: planetary systems; stars:individual ( HAT-P-67); techniques:photometric; techniques:spectroscopic
• Online Access: http://hdl.handle.net/10150/623926; http://arizona.openrepository.com/arizona/handle/10150/623926

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(circle dot) , R-* = 2.546(-0.084)(+0.099) R-circle dot host star in a similar to 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 vsin 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 degrees, 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.