Letter to the Editor

GMRT radio observations of the transiting extrasolar planet HD 189733 b at 244 and 614 MHz^*

¹ CNRS, UMR 7095, Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France e-mail: lecaveli@iap.fr
² UPMC Univ. Paris 6, UMR 7095, Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
³ National Centre for Radio Astrophysics, TIFR, Post Bag 3, Pune University Campus, Pune 411007, India
⁴ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France

Received: 17 April 2009
Accepted: 18 May 2009

Abstract

We report a sensitive search for meter-wavelength emission at 244 and 614 MHz from HD 189733 b, the nearest known extrasolar transiting planet of “hot-Jupiter” type. To discriminate any planetary emission from possible stellar or background contributions, we observed the system for 7.7 h encompassing the planet's eclipse behind the host star. These GMRT observations provide very low (3σ) upper limits of 2 mJy at 244 MHz and 160 μJy at 614 MHz. These limits are, respectively, about 40 and 500 times deeper than those reported recently at a nearby frequency of 340 MHz. Possible explanations of our non-detection include: (1) the Earth being outside the planet's emission beam; (2) its highly variable emission with more rapid flaring than the temporal sampling in our observations; (3) the planetary emission being intrinsically too weak; or more likely; (4) the emission being predominantly at lower frequencies because of a weak planetary magnetic field. We briefly discuss these possibilities and the constraints on this exo-planetary system environment.