Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b

M. Gillon; B. Smalley; L. Hebb; D. R. Anderson; A. H. M. J. Triaud; C. Hellier; P. F. L. Maxted; D. Queloz; D. M. Wilson

doi:10.1051/0004-6361:200810929

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Volume 496 / No 1 (March II 2009)

A&A, 496 1 (2009) 259-267

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Issue		A&A Volume 496, Number 1, March II 2009


Page(s)		259 - 267
Section		Planets and planetary systems
DOI		https://doi.org/10.1051/0004-6361:200810929
Published online		14 January 2009

A&A 496, 259-267 (2009)

Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b ^*

M. Gillon¹, B. Smalley², L. Hebb³, D. R. Anderson², A. H. M. J. Triaud¹, C. Hellier², P. F. L. Maxted², D. Queloz¹ and D. M. Wilson²

¹ Observatoire de Genève, Université de Genève, 51 Chemin des Maillettes, 1290 Sauverny, Switzerland e-mail: michael.gillon@obs.unige.ch
² Astrophysics Group, Keele University, Staffordshire, ST5 5BG, UK
³ School of Physics and Astronomy, University of St. Andrews, North Haugh, Fife, KY16 9SS, UK

Received: 7 September 2008
Accepted: 9 December 2008

Abstract

The gaseous giant planets WASP-4b and WASP-5b are transiting 12-magnitude solar-type stars in the Southern hemisphere. The aim of the present work is to refine the parameters of these systems using high cadence VLT/FORS2 z-band transit photometry and high-resolution VLT/UVES spectroscopy. For WASP-4, the new estimates for the planet radius and mass from a combined analysis of our VLT data with previously published transit photometry and radial velocities are $R_{\rm p} = 1.30^{+0.05}_{-0.04}$ R_J and $M_{\rm p} = 1.21^{+0.13}_{-0.08}$ M_J, resulting in a density $\rho_{\rm p} = 0.55^{+0.04}_{-0.02}$ $\rho_J$ . The radius and mass for the host star are $R_\ast = 0.87^{+0.04}_{-0.03}$ $R_\odot$ and $M_\ast = 0.85^{+0.11}_{-0.07}$ $M_\odot$ . Our ground-based photometry reaches 550 ppm at time sampling of ~50 s. Nevertheless, we also report the presence of an instrumental effect on the VLT that degraded our photometry for the WASP-5 observations. This effect could be a major problem for similar programs. Our new estimates for the parameters of the WASP-5 system are $R_{\rm p} = 1.09$ ± 0.07 R_J, $M_{\rm p} = 1.58^{+0.13}_{-0.10}$ M_J, $\rho_{\rm p} = 1.23 ^{+0.26}_{-0.16}$ $\rho_J$ , $R_\ast = 1.03^{+0.06}_{-0.07}$ $R_\odot$ , and $M_\ast = 0.96^{+0.13}_{-0.09}$ $M_\odot$ . The measured size of WASP-5b agrees well with the basic models of irradiated planets, while WASP-4b is clearly an “anomalously” large planet.

Key words: binaries: eclipsing / planetary systems / stars: individual: WASP-4 / stars: individual: WASP-5 / techniques: photometric / techniques: spectroscopic

^*

Based on data collected with the FORS2 imager at the VLT-UT4 telescope and with the UVES spectrograph at the VLT-UT2 telescope (Paranal Observatory, ESO, Chile) in the programme 280.C-5003.

© ESO, 2009

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Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b *

Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b ^*