Near-Infrared Multi-Band Photometry of the Substellar Companion GJ 758 B

TL;DR

This study provides detailed multi-band infrared photometry of the substellar companion GJ 758 B, revealing methane absorption features and refining its orbital parameters and mass estimate, while also clarifying the nature of a second candidate object.

Contribution

It offers the first comprehensive spectral energy distribution of GJ 758 B across 1-5 microns and refines its orbital and physical properties using new astrometric data.

Findings

Detection of methane absorption at 1.58 microns.

Estimated mass range of 30-40 Jupiter masses.

Confirmed the second candidate as a background star.

Abstract

GJ 758 B is a cold (~600K) companion to a Sun-like star at 29 AU projected separation, which was recently detected with high-contrast imaging. Here we present photometry of the companion in seven photometric bands from Subaru/HiCIAO, Gemini/NIRI and Keck/NIRC2, providing a rich sampling of the spectral energy distribution in the 1-5 micron wavelength range. A clear detection at 1.58 micron combined with an upper limit at 1.69 micron shows methane absorption in the atmosphere of the companion. The mass of the companion remains uncertain, but an updated age estimate indicates that the most likely mass range is ~30-40 Mjup. In addition, we present an updated astrometric analysis that imposes tighter constraints on GJ 758 B's orbit and identifies the proposed second candidate companion, "GJ 758 C", as a background star.