HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed via Doppler Tomography

Creators: Hartman, J. D.; Bakos, G. Á.; Buchhave, L. A.; Torres, G.; Latham, D. W.; Kovács, G.; Bhatti, W.; Csubry, Z.; de Val-Borro, M.; Penev, K.; Huang, C. X.; Béky, B.; Bieryla, A.; Quinn, S. N.; Howard, A. W.; Marcy, G. W.; Johnson, J. A.; Isaacson, H.; Fischer, D. A.; Noyes, R. W.; Falco, E.; Esquerdo, G. A.; Knox, R. P.; Hinz, P.; Lázár, J.; Papp, I.; Sári, P.

Abstract

We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 ± 0.029 mag, T_eff = 7500 ± 250 K main sequence A8V star with a projected rotation velocity of v sin i = 102.1 ± 1.3 km s^-1. We measure the radius of the planet to be R = 1.413 ± 0.054 R_J and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 M_J. Based on theoretical stellar evolution models, the host star has a mass and radius of 1.47 ± 0.12 M_⊙ and 1.500 ± 0.050 R_⊙, respectively. Spectroscopic observations made with Keck-I/HIRES during a partial transit event show the Doppler shadow of HAT-P-57b moving across the average spectral line profile of HAT-P-57, confirming the object as a planetary system. We use these observations, together with analytic formulae that we derive for the line profile distortions, to determine the projected angle between the spin axis of HAT-P-57 and the orbital axis of HAT-P-57b. The data permit two possible solutions, with -16°.7 < λ < 3°.3 or 27°.6 < λ < 57°.4 at 95% confidence, and with relative probabilities for the two modes of 26% and 74%, respectively. Adaptive optics imaging with MMT/Clio2 reveals an object located 2".7 from HAT-P-57 consisting of two point sources separated in turn from each other by 0".22. The H- and L'-band magnitudes of the companion stars are consistent with their being physically associated with HAT-P-57, in which case they are stars of mass 0.61 ± 0.10 M_⊙ and 0.53 ± 0.08 M_⊙. HAT-P-57 is the most rapidly rotating star, and only the fourth main sequence A star, known to host a transiting planet.

Additional Information

© 2015 The American Astronomical Society. Received 2015 September 16; accepted 2015 October 29; published 2015 December 11. We are grateful to the anonymous referee for their careful review of this paper, including several important comments. HATNet operations have been funded by NASA grants NNG04GN74G and NNX13AJ15G. 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 (D. W. L., PI). We would also like to thank J. Pepper for informing us about the KELT observations of this system. 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. 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. This paper presents 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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