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High-precision photometry by telescope defocusing - IV. Confirmation of the huge radius of WASP-17 b

Southworth, John; Hinse, T. C.; Dominik, M.; Fang, X.-S.; Harpsøe, K.; Jørgensen, U. G.; Kerins, E.; Liebig, C.; Mancini, L.; Skottfelt, J.; Anderson, D. R.; Smalley, B.; Tregloan-Reed, J.; Wertz, O.; Alsubai, K. A.; Bozza, V.; Calchi Novati, S.; Dreizler, S.; Gu, S.-H.; Hundertmark, M.; Jessen-Hansen, J.; Kains, N.; Kjeldsen, H.; Lund, M. N.; Lundkvist, M.; Mathiasen, M.; Penny, M. T.; Rahvar, S.; Ricci, D.; Scarpetta, G.; Snodgrass, C. and Surdej, J. (2012). High-precision photometry by telescope defocusing - IV. Confirmation of the huge radius of WASP-17 b. Monthly Notices of the Royal Astronomical Society, 426(2) pp. 1338–1348.

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We present photometric observations of four transits in the WASP-17 planetary system, obtained using telescope defocusing techniques and with scatters reaching 0.5 mmag per point. Our revised orbital period is 4.0 ± 0.6 s longer than previous measurements, a difference of 6.6σ, and does not support the published detections of orbital eccentricity in this system. We model the light curves using the JKTEBOP code and calculate the physical properties of the system by recourse to five sets of theoretical stellar model predictions. The resulting planetary radius, Rb = 1.932 ± 0.052 ± 0.010 RJup (statistical and systematic errors, respectively), provides confirmation that WASP-17 b is the largest planet currently known. All 14 planets with radii measured to be greater than 1.6 RJup are found around comparatively hot (Teff > 5900 K) and massive (MA > 1.15 M) stars. Chromospheric activity indicators are available for eight of these stars, and all imply a low activity level. The planets have small or zero orbital eccentricities, so tidal effects struggle to explain their large radii. The observed dearth of large planets around small stars may be natural but could also be due to observational biases against deep transits, if these are mistakenly labelled as false positives and so not followed up.

Item Type: Journal Item
Copyright Holders: 2012 The Authors
ISSN: 1365-2966
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetNPRP 09-476-1-078Qatar National Research Fund
Keywords: fundamental parameters of stars; planetary systems
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Physical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Research Group: Centre for Electronic Imaging (CEI)
Item ID: 43058
Depositing User: Colin Snodgrass
Date Deposited: 29 May 2015 09:20
Last Modified: 07 Dec 2018 10:31
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