TOI-858 B b: A hot Jupiter on a polar orbit in a loose binary

TL;DR

This paper reports the discovery of a hot Jupiter with a polar orbit around a star in a loose binary system, including its mass, orbital characteristics, and dynamical analysis suggesting a primordial or alternative formation scenario.

Contribution

It presents the first detailed characterization of TOI-858 B b, including its orbit, mass, and misalignment, and investigates its dynamical history in a binary system.

Findings

The planet has a mass of approximately 1.10 M_J.

The orbit is highly misaligned with a sky-projected obliquity of about 99.3 degrees.

The binary companion is too distant for Kozai-Lidov resonance, implying a different migration mechanism.

Abstract

We report the discovery of a hot Jupiter on a 3.28-day orbit around a 1.08 M$_{Sun}$ G0 star that is the secondary component in a loose binary system. Based on follow-up radial velocity observations of TOI-858 B with CORALIE on the Swiss 1.2 m telescope and CHIRON on the 1.5 m telescope at the Cerro Tololo Inter-American Observatory (CTIO), we measured the planet mass to be $1.10\pm 0.08$ M$_{J}$ . Two transits were further observed with CORALIE to determine the alignment of TOI-858 B b with respect to its host star. Analysis of the Rossiter-McLaughlin signal from the planet shows that the sky-projected obliquity is $\lambda = 99.3\pm 3.8$. Numerical simulations show that the neighbour star TOI-858 A is too distant to have trapped the planet in a Kozai-Lidov resonance, suggesting a different dynamical evolution or a primordial origin to explain this misalignment. The 1.15 Msun primary F9 star of the system (TYC 8501-01597-1, at $\rho$ ~11") was also observed with CORALIE in order to provide upper limits for the presence of a planetary companion orbiting that star.