The GAPS Programme with HARPS-N at TNG^{⋆,⋆⋆,⋆⋆⋆}

VIII. Observations of the Rossiter-McLaughlin effect and characterisation of the transiting planetary systems HAT-P-36 and WASP-11/HAT-P-10

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: mancini@mpia.de
² INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
³ Instituto de Astrofísica de Canarias, C/ vía Láctea s/n, 38205, La Laguna, Tenerife, Spain
⁴ Dep. de Astrofísica, Universidad de La Laguna, Avda. Astrofísico F. Sánchez s/n, 38206, La Laguna, Tenerife, Spain
⁵ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Naples, Italy
⁶ Astrophysics Group, Keele University, Keele ST5 5BG, UK
⁷ NASA Ames Research Center, Moffett Field, CA 94035, USA
⁸ INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
⁹ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁰ Centre for Astronomy, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
¹¹ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( Lecco), Italy
¹² INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹³ Fundación Galileo Galilei − INAF, Rambla José Ana Fernandez Pérez, 738712 Breña Baja, Tenerife, Spain
¹⁴ Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano, Italy
¹⁵ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 90134 Palermo, Italy
¹⁶ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁷ INAF – IASF Milano, via Bassini 15, 20133 Milano, Italy
¹⁸ Dip. di Fisica e Astronomia Galileo Galilei, Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy

Received: 5 March 2015
Accepted: 11 May 2015

Abstract

Context. Orbital obliquity is thought to be a fundamental parameter in tracing the physical mechanisms that cause the migration of giant planets from the snow line down to roughly 10^-2 au from their host stars. We are carrying out a large programme to estimate the spin-orbit alignment of a sample of transiting planetary systems to study what the possible configurations of orbital obliquity are and whether they correlate with other stellar or planetary properties.

Aims. We determine the true and the projected obliquity of HAT-P-36 and WASP-11/HAT-P-10 systems, respectively, which are both composed of a relatively cool star (with effective temperature T_eff< 6100  K) and a hot-Jupiter planet.

Methods. Thanks to the high-resolution spectrograph HARPS-N, we observed the Rossiter-McLaughlin effect for both systems by acquiring precise (3−8 m s^-1) radial-velocity measurements during planetary transit events. We also present photometric observations comprising six light curves that cover five transit events, which were obtained using three medium-class telescopes. One transit of WASP-11/HAT-P-10 was followed simultaneously from two observatories. The three transit light curves of HAT-P-36 b show anomalies that are attributable to starspot complexes on the surface of the parent star, in agreement with the analysis of its spectra that indicates moderate activity ( log R′_HK = −4.65 dex). By analysing the complete HATNet data set of HAT-P-36, we estimated the stellar rotation period by detecting a periodic photometric modulation in the light curve caused by star spots, obtaining P_rot = 15.3 ± 0.4 days, which implies that the inclination of the stellar rotational axis with respect to the line of sight is i_⋆ = 65° ± 34°.

Results. We used the new spectroscopic and photometric data to revise the main physical parameters and measure the sky-projected misalignment angle of the two systems. We found λ = −14° ± 18° for HAT-P-36 and λ = 7° ± 5° for WASP-11/HAT-P-10, indicating in both cases a good spin-orbit alignment. In the case of HAT-P-36, we were also able to estimate an upper limit of its real obliquity, which turned out to be ψ< 63 degrees.