The GAPS programme with HARPS-N at TNG

IX. The multi-planet system KELT-6: Detection of the planet KELT-6 c and measurement of the Rossiter-McLaughlin effect for KELT-6 b^⋆,⋆⋆

¹ INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025, Pino Torinese, Italy
e-mail: damasso@oato.inaf.it
² Instituto de Astrofísica de Canarias, C/Via Láctea S/N, 38200, La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain
⁴ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁵ Dip. di Fisica e Astronomia Galileo Galilei – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
⁶ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
⁷ INAF–Osservatorio Astrofisico di Catania, via S.Sofia 78, 95123, Catania, Italy
⁸ INAF–Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
⁹ Dipartimento di Fisica, Universitá di Torino, via P. Giuria 1, 10125 Torino, Italy
¹⁰ Landessternwarte Königstuhl, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹¹ INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate ( LC), Italy
¹² Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08544, USA
¹³ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹⁴ Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA
¹⁵ Fundación Galileo Galilei − INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹⁶ INAF–Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
¹⁷ INAF–IASF Milano, via Bassini 15, 20133 Milano, Italy
¹⁸ INAF–Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁹ Universidad de Atacama, Departamento de Fisica, Copayapu 485, Copiapo, Chile
²⁰ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
²¹ Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK

Received: 19 July 2015
Accepted: 26 August 2015

Abstract

Aims. For more than 1.5 years we spectroscopically monitored the star KELT-6 (BD+31 2447), which is known to host the transiting hot-Saturn KELT-6 b, because a previously observed long-term trend in radial velocity time series suggested that there is an outer companion.

Methods. We collected a total of 93 new spectra with the HARPS-N and TRES spectrographs. A spectroscopic transit of KELT-6 b was observed with HARPS-N, and simultaneous photometry was obtained with the IAC-80 telescope.

Results. We proved the existence of an outer planet with a mininum mass M_psin i = 3.71 ± 0.21 M_Jup and a moderately eccentric orbit (e = 0.21_-0.036^+0.039) of period P ~ 3.5 years. We improved the orbital solution of KELT-6 b and obtained the first measurement of the Rossiter-McLaughlin effect, showing that the planet has a likely circular, prograde, and slightly misaligned orbit with a projected spin-orbit angle of λ = −36 ± 11 degrees. We improved the KELT-6 b transit ephemeris from photometry and provide new measurements of the stellar parameters. KELT-6 appears as an interesting case for studying the formation and evolution of multi-planet systems.