A closer look at LTT 9779b: The ESPRESSO endeavour to pierce the atmospheric veil

Abstract

The proliferation of exoplanet discoveries in exotic environments like the Neptune desert challenges our understanding of planetary atmospheres under intense irradiation. The unexpected discovery of LTT9779 b, an ultra-hot Neptune within this desert, offers a prime opportunity for atmospheric studies. We build on prior observations of LTT9779 b from TESS, Spitzer, and CHEOPS, incorporating new VLT/ESPRESSO data to probe its atmospheric dynamics. Preliminary analyses suggest a metal-rich atmosphere and a high day-side geometric albedo, possibly indicating silicate clouds. Minimal atmospheric escape is observed, contrasting existing models of planetary evolution under extreme irradiation. We obtained the transmission spectrum of LTT9779 b between 0.4 and 0.78 microns with ESPRESSO, addressing systematics across three transits. Our analysis focused on the sodium doublet and H-alpha, using cross-correlation with models containing Na, K, FeH, TiO, and VO. No significant atmospheric signal was detected, with metallicity limits set at [Fe/H] $\ge$ 2.25 ($\ge$ 180 times solar). The non-detection aligns with a high-metallicity, cloud-free model, implying a high mean molecular weight and reduced atmospheric scale height. We interpret this as evidence for a metal-rich atmosphere with suppressed spectral features, possibly due to high-altitude clouds or hazes. These findings are consistent with JWST observations, supporting the hypothesis of metal-rich atmospheres obscured by aerosols in extreme environments.

12 pages, 11 figures, 3 tables, Accepted for publication in Astronomy and Astrophysics

References in corpus (14)

• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• petitRADTRANS: a Python radiative transfer package for exoplanet characterization and retrieval
• On the radiative equilibrium of irradiated planetary atmospheres
• Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum
• Spectrally resolved detection of sodium in the atmosphere of HD189733b with the HARPS spectrograph
• A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
• Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e
• An Ultra-Hot Neptune in the Neptune desert
• The atmosphere of HD 209458b seen with ESPRESSO. No detectable planetary absorptions at high resolution
• WASP-127b: A misaligned planet with a partly cloudy atmosphere and tenuous sodium signature seen by ESPRESSO
• RASSINE: Interactive tool for normalising stellar spectra I. Description and performance of the code
• A New Model of Roche-lobe Overflow for Short-Period Gaseous Planets and Binary Stars
• Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy
• The Hot Neptune WASP-166 b with ESPRESSO II: Confirmation of atmospheric sodium

Cited by in corpus (2)

• HST/WFC3 Constraints on the Abundances of OH and FeH in the Atmosphere of the Ultra-Hot Neptune LTT-9779 b
• TOI-333b: A Neptune Desert planet around a F7V star