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

in Monthly Notices of the Royal Astronomical Society (2012), 426

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 ... [more ▼]

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, R[SUB]b[/SUB] = 1.932 ± 0.052 ± 0.010 R[SUB]Jup[/SUB] (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 R[SUB]Jup[/SUB] are found around comparatively hot (T[SUB]eff[/SUB] > 5900 K) and massive (M[SUB]A[/SUB] > 1.15 M[SUB]&sun;[/SUB]) 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. Based on data collected by MiNDSTEp with the Danish 1.54-m telescope at the ESO La Silla Observatory.Royal Society University Research Fellow. [less ▲]

High-precision photometry by telescope defocusing - III. The transiting planetary system WASP-2 star

in Monthly Notices of the Royal Astronomical Society (2010), 408

ABSTRACT We present high-precision photometry of three transits of the extrasolar planetary system WASP-2, obtained by defocusing the telescopes, and achieving scatters of between 0.42 and 0.73 mmag ... [more ▼]

ABSTRACT We present high-precision photometry of three transits of the extrasolar planetary system WASP-2, obtained by defocusing the telescopes, and achieving scatters of between 0.42 and 0.73 mmag versus the best-fitting model. These data are modelled using the JKTEBOP code, and taking into account the light from the recently discovered faint star close to the system. The physical properties of the WASP-2 system are derived using tabulated predictions from five different sets of stellar evolutionary models, allowing both statistical and systematic error bars to be specified. We find the mass and radius of the planet to be M[SUB]b[/SUB] = 0.846 +/- 0.055 +/- 0.023M[SUB]Jup[/SUB] and R[SUB]b[/SUB] = 1.043 +/- 0.029 +/- 0.015R[SUB]Jup[/SUB]. It has a low equilibrium temperature of 1281 +/- 21K, in agreement with a recent finding that it does not have an atmospheric temperature inversion. The first of our transit data sets has a scatter of only 0.42mmag with respect to the best-fitting light-curve model, which to our knowledge is a record for ground-based observations of a transiting extrasolar planetary system. Based on data collected by MiNDSTEp with the Danish 1.54-m telescope at the ESO La Silla Observatory. E-mail: jkt@astro.keele.ac.uk ‡ Royal Society University Research Fellow. [less ▲]

High-precision photometry by telescope defocussing - II. The transiting planetary system WASP-4

in Monthly Notices of the Royal Astronomical Society (2009)

We present and analyse light curves of four transits of the Southern hemisphere extrasolar planetary system WASP-4, obtained with a telescope defocused so the radius of each point spread function was 17 ... [more ▼]

We present and analyse light curves of four transits of the Southern hemisphere extrasolar planetary system WASP-4, obtained with a telescope defocused so the radius of each point spread function was 17 arcsec (44 pixels). This approach minimizes both random and systematic errors, allowing us to achieve scatters of between 0.60 and 0.88 mmag per observation over complete transit events. The light curves are augmented by published observations and analysed using the JKTEBOP code. The results of this process are combined with theoretical stellar model predictions to derive the physical properties of the WASP-4 system. We find that the mass and radius of the planet are M[SUB]b[/SUB] = 1.289[SUP]+0.090[/SUP][SUB]-0.090[/SUB][SUP]+0.039[/SUP][SUB]-0.000[/SUB]M[SUB]Jup[/SUB] and R[SUB]b[/SUB] = 1.371[SUP]+0.032[/SUP][SUB]-0.035[/SUB][SUP]+0.021[/SUP][SUB]-0.000[/SUB]R[SUB]Jup[/SUB], respectively (statistical and systematic uncertainties). These quantities give a surface gravity and density of g[SUB]b[/SUB] = 17.03[SUP]+0.97[/SUP][SUB]-0.54[/SUB]ms[SUP]-2[/SUP] and rho[SUB]b[/SUB] = 0.500[SUP]+0.032[/SUP][SUB]-0.021[/SUB][SUP]+0.000[/SUP][SUB]-0.008[/SUB] rho[SUB]Jup[/SUB], and fit the trends for short-period extrasolar planets to have relatively high masses and surface gravities. WASP-4 is now one of the best-quantified transiting extrasolar planetary systems, and significant further progress requires improvements to our understanding of the physical properties of low-mass stars. Based on data collected by MiNDSTEp with the Danish 1.54m telescope at the ESO La Silla Observatory. E-mail: jkt@astro.keele.ac.uk â ¡ Royal Society University Research Fellow. [less ▲]