The Hot Neptune WASP-166 b with ESPRESSO – I. Refining the planetary architecture and stellar variability

Abstract

In this paper, we present high-resolution spectroscopic transit observations from ESPRESSO of the super-Neptune WASP-166 b. In addition to spectroscopic ESPRESSO data, we analyse photometric data from TESS of six WASP-166 b transits along with simultaneous NGTS observations of the ESPRESSO runs. These observations were used to fit for the planetary parameters as well as assessing the level of stellar activity (e.g. spot crossings, flares) present during the ESPRESSO observations. We utilize the Reloaded Rossiter McLaughlin (RRM) technique to spatially resolve the stellar surface, characterizing the centre-to-limb convection-induced variations, and to refine the star-planet obliquity. We find WASP-166 b has a projected obliquity of $\lambda = -15.52^{+2.85}_{-2.76}\, ^{\circ }$ and vsin (i) = 4.97 ± 0.09 kms−1 which is consistent with the literature. We were able to characterise centre-to-limb convective variations as a result of granulation on the surface of the star on the order of a few kms−1 for the first time. We modelled the centre-to-limb convective variations using a linear, quadratic and cubic model with the cubic being preferred. In addition, by modelling the differential rotation and centre-to-limb convective variations simultaneously we were able to retrieve a potential anti-solar differential rotational shear (α ∼ -0.5) and stellar inclination (i* either 42.03$^{+9.13}_{-9.60}\, ^{\circ }$ or 133.64$^{+8.42}_{-7.98}\, ^{\circ }$ if the star is pointing towards or away from us). Finally, we investigate how the shape of the cross-correlation functions change as a function of limb angle and compare our results to magnetohydrodynamic simulations.

Dream

“…These results are consistent with those from Hellier et al (2019, v eq sin i ⋆ = 5.1 ± 0.3 km s −1 , λ = 3 ± 5 • ), derived at lower precision from a classical RM analysis of the same HARPS datasets. Our RMR analysis of these three HARPS transits yields a comparable precision on λ than Doyle et al (2022)'s Reloaded RM analysis of two ESPRESSO transits. Our value for λ is consistent with their solid-body fit to the original (−4.49 ± 1.74 • ) and binned (−5.93 ± 2.00 • ) ESPRESSO data, but their values for v eq sin i ⋆ (original, 4.89 ± 0.08 km s −1 ; binned, 4.77 ± 0.09 km s −1 ) are significantly lower than ours.…”

“…The corresponding BIC is however the same than for a constant line profile, and the values for v eq sin i ⋆ and λ are unchanged, so that we adopt this simpler model. Doyle et al (2022) further conclude that the ESPRESSO data is best modeled by solid-body rotation plus quadratic convective RV motions when fit at its original temporal resolution, or by solid-body rotation plus cubic convective RV motions when fit at a downsampled resolution of 10 min to mitigate p-mode oscillations. They further claim a constraint on differential rotation when modeled together with linear convective RV motions.…”

“…There is a hint that the local stellar line started evolving in the last epoch, but BIC comparison favors a common line profile for all three visits. Analyzing two ESPRESSO transits with the reloaded RM method (Cegla et al 2016), Doyle et al (2022) noticed that the FWHM of the local line profile appears to increase linearly with µ toward the stellar limb, with a slope of about 2.4 km s −1 . Interestingly the HARPS data appears to confirm this hint, with a slope of 2.3 ± 0.8 km s −1 when allowing the width of our model line profile to vary linearly with µ.…”

“…They further claim a constraint on differential rotation when modeled together with linear convective RV motions. To compare with the results from Doyle et al (2022) we fit these various models to the HARPS data at its original temporal resolution or binned by two exposures to reach a 10 min resolution. We find that the HARPS data, at their original or binned resolution, are not sensitive enough to constrain convective motions and/or differential rotation with coefficients consistent with zero and BIC values significantly larger than for a pure solid-body model.…”

DREAM I. Orbital architecture orrery

“…These results are consistent with those from Hellier et al (2019) (v eq sin i ‹ = 5.1 ˘0.3 km s ´1, λ = 3 ˘5 ˝), derived at lower precision from a classical RM analysis of the same HARPS datasets. Our RM Revolutions analysis of these three HARPS transits yields a comparable precision on λ than Doyle et al (2022)'s Reloaded RM analysis of two ESPRESSO transits. Our value for λ is consistent with their solid-body fit to the original (´4.49 ˘1.74 ˝) and binned (´5.93 ˘2.00 ˝) ESPRESSO data, but their values for v eq sin i ‹ (original, 4.89 ˘0.08 km s ´1; binned, 4.77 ˘0.09 km s ´1) are significantly lower than ours.…”