Stone, Jordan M.Jordan M.StoneEisner, JoshJoshEisnerSkemer, AndyAndySkemerMorzinski, Katie M.Katie M.MorzinskiClose, LairdLairdCloseMales, JaredJaredMalesRodigas, Timothy J.Timothy J.RodigasHinz, PhilPhilHinzPUGLISI, Alfio TimothyAlfio TimothyPUGLISI2020-05-072020-05-0720160004-637Xhttp://hdl.handle.net/20.500.12386/24609L-band spectroscopy is a powerful probe of cool low-gravity atmospheres: the P, Q, and R branch fundamental transitions of methane near 3.3 μm provide a sensitive probe of carbon chemistry; cloud thickness modifies the spectral slope across the band; and {{{H}}}<SUB>3</SUB><SUP>+</SUP> 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 μm 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<SUB>4</SUB> chemistry.STAMPAenArticle10.3847/0004-637X/829/1/392-s2.0-84991088899000385374500039https://iopscience.iop.org/article/10.3847/0004-637X/829/1/39https://arxiv.org/pdf/1608.02597.pdf2016ApJ...829...39SFIS/05 - ASTRONOMIA E ASTROFISICA