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See detailTransit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star
Van Grootel, Valérie ULg; Gillon, Michaël ULg; Valencia, D. et al

in Astrophysical Journal (in press)

Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition ... [more ▼]

Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition. We present here the confirmation, based on Spitzer transit observations, that the super-Earth HD 97658 b transits its host star. HD 97658 is a low-mass ($M_*=0.77\pm0.05\,M_{\odot}$) K1 dwarf, as determined from the Hipparcos parallax and stellar evolution modeling. To constrain the planet parameters, we carry out Bayesian global analyses of Keck-HIRES radial velocities, and MOST and Spitzer photometry. HD 97658 b is a massive ($M_P=7.55^{+0.83}_{-0.79} M_{\oplus}$) and large ($R_{P} = 2.247^{+0.098}_{-0.095} R_{\oplus}$ at 4.5 $\mu$m) super-Earth. We investigate the possible internal compositions for HD 97658 b. Our results indicate a large rocky component, by at least 60% by mass, and very little H-He components, at most 2% by mass. We also discuss how future asteroseismic observations can improve the knowledge of the HD 97658 system, in particular by constraining its age. Orbiting a bright host star, HD 97658 b will be a key target for coming space missions TESS, CHEOPS, PLATO, and also JWST, to characterize thoroughly its structure and atmosphere. [less ▲]

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See detailImproved precision on the radius of the nearby super-Earth 55 Cnc e
Gillon, Michaël ULg; Demory, B.-O.; Benneke, B. et al

in Astronomy and Astrophysics (2012), 539

We report on new transit photometry for the super-Earth 55 Cnc e obtained with Warm Spitzer/IRAC at 4.5 microns. An individual analysis of these new data leads to a planet radius of 2.21-0.16+0.15 Rearth ... [more ▼]

We report on new transit photometry for the super-Earth 55 Cnc e obtained with Warm Spitzer/IRAC at 4.5 microns. An individual analysis of these new data leads to a planet radius of 2.21-0.16+0.15 Rearth, in good agreement with the values previously derived from the MOST and Spitzer transit discovery data. A global analysis of both Spitzer transit time-series improves the precision on the radius of the planet at 4.5 microns to 2.20+-0.12 Rearth. We also performed an independent analysis of the MOST data, paying particular attention to the influence of the systematic effects of instrumental origin on the derived parameters and errors by including them in a global model instead of performing a preliminary detrending-filtering processing. We deduce from this reanalysis of MOST data an optical planet radius of 2.04+-0.15 Rearth that is consistent with our Spitzer infrared radius. Assuming the achromaticity of the transit depth, we performed a global analysis combining Spitzer and MOST data that results in a planet radius of 2.17+-0.10 Rearth (13,820+-620 km). These results confirm that the most probable composition of 55 Cnc e is an envelope of supercritical water above a rocky nucleus. [less ▲]

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See detailDetection of a transit of the super-Earth 55 Cnc e with Warm Spitzer
Demory, B.-O.; Gillon, Michaël ULg; Deming, D. et al

in Astronomy and Astrophysics (2011), 533

We report on the detection of a transit of the super-Earth 55 Cnc e with warm Spitzer in IRAC's 4.5 μm band. Our MCMC analysis includes an extensive modeling of the systematic effects affecting warm ... [more ▼]

We report on the detection of a transit of the super-Earth 55 Cnc e with warm Spitzer in IRAC's 4.5 μm band. Our MCMC analysis includes an extensive modeling of the systematic effects affecting warm Spitzer photometry, and yields a transit depth of 410 ± 63 ppm, which translates to a planetary radius of 2.08+0.16-0.17 R_oplus as measured in IRAC 4.5 μm channel. A planetary mass of 7.81-0.53+0.58 M_oplus is derived from an extensive set of radial-velocity data, yielding a mean planetary density of 4.78-1.20+1.31 g cm-3. Thanks to the brightness of its host star (V = 6, K = 4), 55 Cnc e is a unique target for the thorough characterization of a super-Earth orbiting around a solar-type star. [less ▲]

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