WTS-2 b: Too close for comfort?

¹ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
² Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85741 Garching, Germany
³ Departamento de Astrofísica, Centro de Astrobiología (CSIC/INTA), PO Box 78, 28691 Villanueva de la Canada, Spain
⁴ Universitatssternwarte Scheinerstrasse 1, 81679 Munchen, Germany
⁵ Main Astronomical Observatory of Ukrainian Academy of Sciences, Golosiiv Woods, Kyiv-127, 03680, Ukraine
⁶ Departamento de Física Teórica, Faculdad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, España
⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁸ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK

^a e-mail: birkby@strw.leidenuniv.nl

Abstract

We report the discovery of WTS-2 b, a typical hot Jupiter in an unusually close 1.02-day orbit to a K-dwarf star. This is the second planet to be discovered in the infrared light curves of the WFCAM Transit Survey (WTS) and is only one-and-a-half times the separation from its host star at which is would be destroyed by Roche lobe overflow. The predicted remaining lifetime of the planet is just 38 Myrs, assuming a tidal dissipation quality factor of Q'_* = 10⁶. The magnitude of Q'_* is largely unconstrained by observations, thus WTS-2 b provides a useful calibration point for theories describing how frictional processes within a host star affect the tidal orbital evolution of its companion giant planets. It is expected that stars with large convective envelopes are more efficient at dissipating the orbital energy of the planet, and WTS-2 b provides an observational constraint in the sparsely populated K-dwarf regime. In addition, despite its relatively faint magnitude, the favourable size ratio of the WTS-2 star-planet system and the predicted hot equilibrium temperature of the planet will make it possible to characterise the planet's atmosphere via secondary eclipse measurements using existing ground-based instrumentation.