HATS-38 b and WASP-139 b join a growing group of hot Neptunes on polar orbits
Juan I. Espinoza-Retamal, Gu{\dh}mundur Stef\'ansson, Cristobal Petrovich, Rafael Brahm, Andr\'es Jord\'an, Elyar Sedaghati, Jennifer P. Lucero, Marcelo Tala Pinto, Diego J. Mu\~noz, Gavin Boyle, Rodrigo Leiva, Vincent Suc

TL;DR
This study measures the sky-projected obliquities of two hot Neptune exoplanets, revealing they are on polar orbits, and discusses their possible high-eccentricity migration origins and the broader obliquity distribution of such planets.
Contribution
Introduces a new modeling code, ironman, for joint fitting of transit, RV, and RM data, and provides the first obliquity measurements for these two hot Neptunes.
Findings
Both planets have high obliquities, indicating polar orbits.
The planets' eccentricities are consistent with circular orbits.
Hierarchical Bayesian analysis suggests a higher prevalence of polar orbits among hot Neptunes.
Abstract
We constrain the sky-projected obliquities of two low-density hot Neptune planets, HATS-38 b and WASP-139 b, orbiting nearby G and K stars using Rossiter-McLaughlin (RM) observations with VLT/ESPRESSO, yielding deg and deg, respectively. To model the RM effect, we use a new publicly available code, ironman, which is capable of jointly fitting transit photometry, Keplerian radial velocities, and RM effects. WASP-139 b has a residual eccentricity while HATS-38 b has an eccentricity of , which is compatible with a circular orbit given our data. Using the obliquity constraints, we show that they join a growing group of hot and low-density Neptunes on polar orbits. We use long-term radial velocities to rule out companions with masses within au. We show that…
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Taxonomy
TopicsAstro and Planetary Science · Spacecraft and Cryogenic Technologies · Space Exploration and Technology
