Can we detect the stellar differential rotation of WASP-7 through the Rossiter–McLaughlin observations?

et al. 2020

A&A

123

Context. Ultra-hot Jupiters are excellent laboratories for the study of exoplanetary atmospheres. WASP-121b is one of the most studied; many recent analyses of its atmosphere report interesting features at different wavelength ranges. Aims. In this paper we analyze one transit of WASP-121b acquired with the high-resolution spectrograph ESPRESSO at VLT in one-telescope mode, and one partial transit taken during the commissioning of the instrument in four-telescope mode. Methods. We take advantage of the very high S/N data and of the extreme stability of the spectrograph to investigate the anomalous in-transit radial velocity curve and study the transmission spectrum of the planet. We pay particular attention to the removal of instrumental effects, and stellar and telluric contamination. The transmission spectrum is investigated through single-line absorption and cross-correlation with theoretical model templates. Results. By analyzing the in-transit radial velocities we were able to infer the presence of the atmospheric Rossiter-McLaughlin effect. We measured the height of the planetary atmospheric layer that correlates with the stellar mask (mainly Fe) to be 1.052±0.015 R p and we also confirmed the blueshift of the planetary atmosphere. By examining the planetary absorption signal on the stellar cross-correlation functions we confirmed the presence of a temporal variation of its blueshift during transit, which could be investigated spectrum-by-spectrum thanks to the quality of our ESPRESSO data. We detected significant absorption in the transmission spectrum for Na, H, K, Li, Ca ii, and Mg, and we certified their planetary nature by using the 2D tomographic technique. Particularly remarkable is the detection of Li, with a line contrast of ∼0.2% detected at the 6σ level. With the cross-correlation technique we confirmed the presence of Fe i, Fe ii, Cr i, and V i. Hα and Ca ii are present up to very high altitudes in the atmosphere (∼1.44 R p and ∼2 R p , respectively), and also extend beyond the transit-equivalent Roche lobe radius of the planet. These layers of the atmosphere have a large line broadening that is not compatible with being caused by the tidally locked rotation of the planet alone, and could arise from vertical winds or high-altitude jets in the evaporating atmosphere.

Section: Fourier Transform Of the Ccfmentioning

confidence: 90%

Atmospheric Rossiter–McLaughlin effect and transmission spectroscopy of WASP-121b with ESPRESSO

Borsa

Allart

et al. 2020

A&A

123

“…On the other hand, solarlike differential rotation can become important in main sequence stars (Karoff et al 2018) and it is expected to be stronger in F-G stars (Balona & Abedigamba 2016). In our calculations, we assume solid-body rotation, meaning that we are not considering the amplitude variation of the RM signal that could be introduced by this effect (Serrano et al 2020).…”

Section: Accuracy Of the Modelled Transit Effectsmentioning

confidence: 99%

The atmosphere of HD 209458b seen with ESPRESSO

Pallé

Stangret

et al. 2021

A&A

We observed two transits of the iconic gas giant HD 209458b between 380 and 780 nm, using the high-resolution ESPRESSO spectrograph. The derived planetary transmission spectrum exhibits features at all wavelengths where the parent star shows strong absorption lines, for example, Na I, Mg I, Fe I, Fe II, Ca I, V I, Hα, and K I. We interpreted these features as the signature of the deformation of the stellar line profiles due to the Rossiter-McLaughlin effect, combined with the centre-to-limb effects on the stellar surface, which is in agreement with similar reports recently presented in the literature. We also searched for species that might be present in the planetary atmosphere but not in the stellar spectra, such as TiO and VO, and obtained a negative result. Thus, we find no evidence of any planetary absorption, including previously reported Na I, in the atmosphere of HD 209458b. The high signal-to-noise ratio in the transmission spectrum (~1700 at 590 nm) allows us to compare the modelled deformation of the stellar lines in assuming different one-dimensional stellar atmospheric models. We conclude that the differences among various models and observations remain within the precision limits of the data. However, the transmission light curves are better explained when the centre-to-limb variation is not included in the computation and only the Rossiter-McLaughlin deformation is considered. This demonstrates that ESPRESSO is currently the best facility for spatially resolving the stellar surface spectrum in the optical range using transit observations and carrying out empirical validations of stellar models.

“…The overestimation of vsin(i) could have variety of reasons. For instance, the RM signal can be affected by second-order effects such as the convective blueshift and granulation (Shporer & Brown 2011;Cegla et al 2016b), stellar differential rotation (Hirano et al 2011;Hirano 2014;Albrecht et al 2012;Cegla et al 2016b;Serrano et al 2020), microlensing effect due to the transiting planet's mass (Oshagh et al 2013), impact of ringed exoplanet on RM signal (Akinsanmi et al 2018;de Mooij et al 2017), occulted stellar active regions (Oshagh et al 2016(Oshagh et al , 2018, nonocculted stellar active regions (Boldt et al 2020), and also inaccurate estimations of stellar limb darkening (Csizmadia et al 2013;Yan et al 2015). Some of these effects will have minor impact on the RM shape and amplitude (such as microlensing and ring around the planet), however, some like the stellar active region occulation and stellar differential rotation could cause significant deformation of the RM shape and also alter its amplitude.…”

Section: Modeling Rm With Additional Gaussian Processmentioning

confidence: 99%

Transmission spectroscopy and Rossiter-McLaughlin measurements of the young Neptune orbiting AU Mic

Πάλλη

Oshagh

et al. 2020

A&A

AU Mic b is a Neptune-sized planet on an 8.47-day orbit around the nearest pre-main sequence (~20 Myr) star to the Sun, the bright (V = 8.81) M dwarf AU Mic. The planet was preliminary detected in Doppler radial velocity time series and recently confirmed to be transiting with data from the TESS mission. AU Mic b is likely to be cooling and contracting and might be accompanied by a second, more massive planet, in an outer orbit. Here, we present the observations of the transit of AU Mic b using ESPRESSO on the Very Large Telescope. We obtained a high-resolution time series of spectra to measure the Rossiter-McLaughlin effect, to constrain the spin-orbit alignment of the star and planet, and to simultaneously attempt to retrieve the planet’s atmospheric transmission spectrum. These observations allowed us to study, for the first time, the early phases of the dynamical evolution of young systems. We applied different methodologies to derive the spin-orbit angle of AU Mic b, and all of them retrieve values consistent with the planet being aligned with the rotation plane of the star. We determined a conservative spin-orbit angle λ value of −2.96−10.30+10.44 degrees, indicative that the formation and migration of the planets of the AU Mic system occurred within the disc. Unfortunately, and despite the large signal-to-noise ratio of our measurements, the degree of stellar activity prevented us from detecting any features from the planetary atmosphere. In fact, our results suggest that transmission spectroscopy for recently formed planets around active young stars is going to remain very challenging, if at all possible, for the near future.