The slow spin of the young sub-stellar companion GQ Lupi b and its orbital configuration

TL;DR

This study measures the slow rotation and orbital velocity of the young exoplanet GQ Lupi b, providing insights into its formation process by analyzing high-resolution spectra and atmospheric composition.

Contribution

First measurement of the projected rotational velocity and barycentric radial velocity of GQ Lupi b, revealing its slow spin and informing formation theories.

Findings

GQ Lupi b has a projected rotational velocity of about 5.3 km/s.

The system's radial velocity is measured at approximately 2.0 km/s.

GQ Lupi b is a slow rotator likely due to its young age and ongoing accretion.

Abstract

The spin of a planet or brown dwarf is related to the accretion process, and therefore studying spin can help promote our understanding of the formation of such objects. We present the projected rotational velocity of the young sub-stellar companion GQ Lupi b, along with its barycentric radial velocity. The directly imaged exoplanet or brown dwarf companion joins a small but growing ensemble of wide-orbit sub-stellar companions with a spin measurement. The GQ Lupi system was observed at high spectral resolution (R ~ 100000), and in the analysis we made use of both spectral and spatial filtering to separate the signal of the companion from that of the host star. We detect both CO (S/N=11.6) and H2O (S/N=7.7) in the atmosphere of GQ Lupi b by cross-correlating with model spectra, and we find it to be a slow rotator with a projected rotational velocity of $5.3^{+0.9}_{-1.0}$ km/s. The slow rotation is most likely due to its young age of < 5 Myr, as it is still in the process of accreting material and angular momentum. We measure the barycentric radial velocity of GQ Lupi b to be $2.0 \pm 0.4$ km/s, and discuss the allowed orbital configurations and their implications for formation scenarios for GQ Lupi b.