High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP)

I. Lucky imaging observations of 101 systems in the southern hemisphere^⋆,⋆⋆

¹ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
e-mail: d.f.evans@keele.ac.uk
² Centre for Electronic Imaging, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
³ Niels Bohr Institute & Centre for Star and Planet Formation, University of Copenhagen Øster Voldgade 5, 1350 Copenhagen, Denmark
⁴ SUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
⁵ Qatar Environment and Energy Research Institute (QEERI), HBKU, Qatar Foundation, Doha, Qatar
⁶ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁷ Dipartimento di Fisica “E.R. Caianiello”, Università di Salerno, via Giovanni Paolo II 132, 84084 Fisciano, Italy
⁸ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy
⁹ Meteorologisches Institut, Universität Hamburg, Bundesstraße 55, 20146 Hamburg, Germany
¹⁰ Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹¹ Istituto Internazionale per gli Alti Studi Scientifici (IIASS), via G. Pellegrino 19, 84019 Vietri sul Mare ( SA), Italy
¹² European Southern Observatory, Karl-Schwarzschild Straße 2, 85748 Garching bei München, Germany
¹³ Yunnan Observatories, Chinese Academy of Sciences, 650011 Kunming, PR China
¹⁴ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650011 Kunming, PR China
¹⁵ Korea Astronomy & Space Science Institute, 776 Daedukdae-ro, Yuseong-gu, 305-348 Daejeon, Republic of Korea
¹⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁷ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹⁸ Finnish Centre for Astronomy with ESO (FINCA), Väisäläntie 20, 21500 Piikkiö, Finland
¹⁹ Unidad de Astronomía, Fac. de Ciencias Básicas, Universidad de Antofagasta, Avda. U. de Antofagasta 02800, Antofagasta, Chile
²⁰ CITEUC – Centre for Earth and Space Science Research of the University of Coimbra, Observatório Astronómico da Universidade de Coimbra, 3030-004 Coimbra, Portugal
²¹ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
²² Department of Physics, Sharif University of Technology, PO Box 11155, 9161 Tehran, Iran
²³ Astronomisches Rechen-Institut, Zentrum für Astronomie, Universität Heidelberg, Mönchhofstraße 12-14, 69120 Heidelberg, Germany
²⁴ Planetary and Space Sciences, Department ofPhysical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
²⁵ Institut d’Astrophysique et de Géophysique, Allée du 6 Août 17, Sart Tilman, Bât. B5c, 4000 Liège, Belgium
²⁶ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark

Received: 15 December 2015
Accepted: 9 March 2016

Abstract

Context. Wide binaries are a potential pathway for the formation of hot Jupiters. The binary fraction among host stars is an important discriminator between competing formation theories, but has not been well characterised. Additionally, contaminating light from unresolved stars can significantly affect the accuracy of photometric and spectroscopic measurements in studies of transiting exoplanets.

Aims. We observed 101 transiting exoplanet host systems in the Southern hemisphere in order to create a homogeneous catalogue of both bound companion stars and contaminating background stars, in an area of the sky where transiting exoplanetary systems have not been systematically searched for stellar companions. We investigate the binary fraction among the host stars in order to test theories for the formation of hot Jupiters.

Methods. Lucky imaging observations from the Two Colour Instrument on the Danish 1.54 m telescope at La Silla were used to search for previously unresolved stars at small angular separations. The separations and relative magnitudes of all detected stars were measured. For 12 candidate companions to 10 host stars, previous astrometric measurements were used to evaluate how likely the companions are to be physically associated.

Results. We provide measurements of 499 candidate companions within 20 arcsec of our sample of 101 planet host stars. 51 candidates are located within 5 arcsec of a host star, and we provide the first published measurements for 27 of these. Calibrations for the plate scale and colour performance of the Two Colour Instrument are presented.

Conclusions. We find that the overall multiplicity rate of the host stars is 38⁺¹⁷_-13 %, consistent with the rate among solar-type stars in our sensitivity range, suggesting that planet formation does not preferentially occur in long period binaries compared to a random sample of field stars. Long period stellar companions (P> 10 yr) appear to occur independently of short period companions, and so the population of close-in stellar companions is unconstrained by our study.