The highest resolution near infrared spectrum of the imaged planetary mass companion 2M1207?b

摘要

Direct-imaging searches for planets reveal wide orbitplanets amenable to spectroscopy, and their atmospheres represent animportant comparison to the irradiated atmospheres of Hot Jupiters.Using AO integral field spectroscopy of 2M1207b, the shape of thecontinuumemission over the J, H, and Kbands from the atmosphere of this young,planetary mass companion is measured in order to compare with atmospheric andevolutionary models, and objects of similar temperature in young clusters andthe field. The 2M1207b spectrum has the highest spectral resolution()and largest wavelength coverage, including the firstJ-band spectrum, for this benchmark object. The high signal-to-noise of thedata allow a clear identification of signatures of low surface gravity, andcomparison with a grid of AMES-Dusty models reveals a best-fit effectivetemperature of = 1600K with a preferred surface gravity of logg=4.5.The J-band flux is depressed relative to nearly all L-type objects, and thedetailed shape of the absorption features across the H-band exhibitdifferences from the model predictions. The possible origins of 2M1207b andits low luminosity are examined with the new data and analysis whichsuggest that extinction from a disk with large grains is a viable scenarioand is preferred over scatttering off an optically thick disk. The 2M1207bspectrum presents an important comparison for the types of features whichmay be present in upcoming spectra of the atmospheres of planets imaged inorbit around stellar primaries.Key words: planetary systems - brown dwarfs - planets andsatellites: atmospheres - binaries: close - techniques: high angularresolution