The atmosphere of the warm Neptune GJ 436 b probed with ESPRESSO
E. Herrero-Cisneros, M. R. Zapatero Osorio, J. Sanz-Forcada, R. Allart, T. Azevedo Silva, S. Cristiani, A. R. Costa Silva, Y. C. Damasceno, P. Di Marcantonio, P. Figueira, J. I. Gonz\'alez Hern\'andez, B. Lavie, M. Lendl, G. Lo Curto, C. J. A. P. Martins, E. Pall\'e, F. Pepe

TL;DR
This study used ESPRESSO transmission spectroscopy to search for atomic and molecular signatures in GJ 436 b's atmosphere, finding no definitive detections but setting upper limits and noting stellar activity effects.
Contribution
First high-resolution optical transmission spectroscopy of GJ 436 b with ESPRESSO, providing constraints on atmospheric composition and stellar activity influence.
Findings
No strong planetary absorption features detected.
A tentative Fe I signal at -18.6 km/s with low significance.
Stellar flares observed affecting chromospheric lines.
Abstract
Aims. We aim to identify the presence of atomic and molecular species in the upper atmosphere of the warm Neptune-sized transiting planet GJ 436 b, which has a radiative equilibrium temperature of 690 K and a mass of 25.4 Earth masses. Methods. Using transmission spectroscopy, we observed two full transits of GJ 436 b with the ESPRESSO spectrograph, covering the wavelength range from 3800 to 7880 Angstrom. We searched for traces of atomic (H I, Li I, Na I, Mg I, V I, Cr I, Fe I, and Fe II) and molecular (TiO, VO) species by directly detecting planetary absorption features and by cross-correlating the planetary spectrum with theoretical spectra computed for each investigated species. Results. Our analysis reveals no strong planetary detection for any of the species, consistent with a featureless optical spectrum. We derived upper limits by combining all ESPRESSO observations.…
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