The highest resolution near infrared spectrum of the imaged planetary mass companion 2M1207 b ^*,**

¹ Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK e-mail: [patience;rob;derosa]@astro.ex.ac.uk
² National Research Council Canada, Herzberg Institute of Astrophysics, BC V9E 2E7, Victoria, Canada e-mail: christian.marois@nrc-cnrc.gc.ca

Received: 27 January 2010
Accepted: 20 March 2010

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 T _eff= 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.