Detectability of planetary rings around an extrasolar planet from reflected-light photometr.pdf

a r X i v : a s t r o - p h / 0 5 1 0 5 9 4 v 1 1 9 O c t 2 0 0 5 Direct Imaging of Exoplanets: Science and Techniques Proceedings IAU Colloquium No. 200, 2005 Claude Aime, Farrokh Vakili, eds. c? 2005 International Astronomical Union DOI: 00.0000/X000000000000000X Detectability of planetary rings around an extrasolar planet from reflected-light photometry L. Arnold1 and J. Schneider2 1CNRS - Observatoire de Haute-Provence 04870 Saint-Michel-l’Observatoire, France email: arnold at obs-hp.fr 2Observatoire de Paris-Meudon, 92195, Meudon Cedex, France email: Jean.Schneider at obspm.fr Abstract. The next generation of high-contrast imaging instruments will provide the first unre- solved image of an extrasolar planet. While the emitted infrared light from the planet in thermal equilibrium should show almost no phase effect, the reflected visible light will vary with the or- bital phase angle. We study the photometric variation of the reflected light with orbital phase of a ringed extrasolar planet. We show that a ring around an extrasolar planet, both obviously unresolved, can be detected by its specific photometric signature. Keywords. Stars: planetary systems – Planets: rings – Extrasolar planet characterization 1. Introduction The discovery of extrasolar planets by radial velocity measurements has provided the first dynamical characteristics of planets (orbital elements and mass). The next step will be to investigate physical characteristics of extrasolar (albedo, temperature, radius etc.) and their surroundings. Among the latter are planetary rings. Coming space or ground- based high-contrast imaging instruments will be able to provide the first image of an unresolved extrasolar planet, in the thermal infrared or in the visible light. The emitted thermal infrared light from the planet should show no phase effect assuming the planet is in thermal equilibrium. But the reflected visible light will vary with phase angle, as should be shown by a broad-band photometri