The highest resolution near-IR spectrum of the imaged planetary mass companion 2M1207 b

TL;DR

This study presents the highest resolution near-infrared spectrum of the planetary mass companion 2M1207 b, revealing atmospheric features, low surface gravity signatures, and suggesting disk extinction as a possible cause for its low luminosity.

Contribution

It provides the first high-resolution J-band spectrum of 2M1207 b, enabling detailed atmospheric analysis and comparison with models, advancing understanding of young planetary atmospheres.

Findings

Effective temperature of 1600 K from model fitting

Detection of low surface gravity signatures

Evidence supporting disk extinction over scattering

Abstract

Direct-imaging searches for planets reveal wide orbit planets amenable to spectroscopy, and their atmospheres represent an important comparison to the irradiated atmospheres of Hot Jupiters. Using AO integral field spectroscopy of 2M1207 b, the shape of the continuum emission over the J, H, and K bands from the atmosphere of this young, planetary mass companion is measured in order to compare with atmospheric and evolutionary models, and objects of similar temperature in young clusters and the field. The 2M1207 b spectrum has the highest spectral resolution (R~300-1500) and largest wavelength coverage, including the first J-band spectrum, for this benchmark object. The high signal-to-noise of the data allow a clear identification of signatures of low surface gravity, and comparison with a grid of AMES-Dusty models reveals a best-fit effective temperature of Teff=1600 K with a preferred surface gravity of log g=4.5. The J-band flux is depressed relative to nearly all L-type objects, and the detailed shape of the absorption features across the H-band exhibit differences from the model predictions. The possible origins of 2M1207 b and its low luminosity are examined with the new data and analysis which suggest that extinction from a disk with large grains is a viable scenario and is preferred over scatttering off an optically thick disk. The 2M1207 b spectrum presents an important comparison for the types of features which may be present in upcoming spectra of the atmospheres of planets imaged in orbit around stellar primaries.