L-band Spectroscopy with Magellan-AO/Clio2: First Results on Young Low-Mass Companions

Abstract

L-band spectroscopy is a powerful probe of cool low-gravity atmospheres: The P, Q, and R branch fundamental transitions of methane near 3.3 $\mu$m provide a sensitive probe of carbon chemistry; cloud thickness modifies the spectral slope across the band; and H${}_3^{+}$ opacity can be used to detect aurorae. Many directly imaged gas-giant companions to nearby young stars exhibit L-band fluxes distinct from the field population of brown dwarfs at the same effective temperature. Here we describe commissioning the L-band spectroscopic mode of Clio2, the 1-5 $\mu$m instrument behind the Magellan adaptive-optics system. We use this system to measure L-band spectra of directly imaged companions. Our spectra are generally consistent with the parameters derived from previous near-infrared spectra for these late M to early L type objects. Therefore, deviations from the field sequence are constrained to occur below 1500 K. This range includes the L-T transition for field objects and suggests that observed discrepancies are due to differences in cloud structure and CO/CH${}_4$ chemistry.

Accepted to ApJ

References in corpus (8)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Detection of Carbon Monoxide and Water Absorption Lines in an Exoplanet Atmosphere
• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• Search for Associations Containing Young stars (SACY): I. Sample & Searching Method
• Simultaneous Detection of Water, Methane and Carbon Monoxide in the Atmosphere of Exoplanet HR8799b
• A Systematic Study of Departures from Chemical Equilibrium in the Atmospheres of Substellar Mass Objects
• Clio: a 3-5 micron AO planet-finding camera

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• The planetary-mass-limit VLT/SINFONI library: Spectral extraction and atmospheric characterization via forward modeling
• L-band Integral Field Spectroscopy of the HR 8799 Planetary System