DIRECTLY IMAGED L-T TRANSITION EXOPLANETS IN THE MID-INFRARED

作者：Skemer Andrew J^*; Marley Mark S; Hinz Philip M; Morzinski Katie M; Skrutskie Michael F; Leisenring Jarron M; Close Laird M; Saumon Didier; Bailey Vanessa P; Briguglio Runa; Defrere Denis; Esposito Simone; Follette Katherine B; Hill John M; Males Jared R; Puglisi Alfio; Rodigas Timothy J; Xompero Marco

来源：Astrophysical Journal, 2014, 792(1): 17.

DOI：10.1088/0004-637X/792/1/17

• brown dwarfs
• infrared: planetary systems
• instrumentation: adaptive optics
• planets and satellites: atmospheres
• planets and satellites: gaseous planets
• stars: individual (HR 8799 2M1207 b)

Gas-giant planets emit a large fraction of their light in the mid-infrared (greater than or similar to 3 mu m), where photometry and spectroscopy are critical to our understanding of the bulk properties of extrasolar planets. Of particular importance are the L- and M-band atmospheric windows (3-5 mu m), which are the longest wavelengths currently accessible to ground-based, high-contrast imagers. We present binocular LBT adaptive optics (AO) images of the HR 8799 planetary system in six narrow-band filters from 3 to 4 mu m, and a Magellan AO image of the 2M1207 planetary system in a broader 3.3 mu m band. These systems encompass the five known exoplanets with luminosities consistent with L -> T transition brown dwarfs. Our results show that the exoplanets are brighter and have shallower spectral slopes than equivalent temperature brown dwarfs in a wavelength range that contains the methane fundamental absorption feature (spanned by the narrow-band filters and encompassed by the broader 3.3 mu m filter). For 2M1207 b, we find that thick clouds and non-equilibrium chemistry caused by vertical mixing can explain the object's appearance. For the HR 8799 planets, we present new models that suggest the atmospheres must have patchy clouds, along with non-equilibrium chemistry. Together, the presence of a heterogeneous surface and vertical mixing presents a picture of dynamic planetary atmospheres in which both horizontal and vertical motions influence the chemical and condensate profiles.

• 出版日期2014-9-1
• 单位Los Alamos