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

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


We present the discovery of HAT-P-57b, a P = 2.4653 day transiting planet around a V = 10.465 ± 0.029 mag, Teff = 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 RJ and, based on RV observations, place a 95% confidence upper limit on its mass of M < 1.85 MJ. 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 < l < 3°.3 or 27°.6 < l < 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.

Original languageEnglish (US)
Article number197
JournalAstronomical Journal
Issue number6
StatePublished - Dec 1 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • planetary systems
  • stars: individual (HAT-P-57)
  • techniques: photometric
  • techniques: spectroscopic


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