CLOUD ATLAS: HUBBLE SPACE TELESCOPE NEAR-INFRARED SPECTRAL LIBRARY OF BROWN DWARFS, PLANETARY-MASS COMPANIONS, AND HOT JUPITERS

We present a uniform, high-quality spectral library (1.10-1.69 microns) of the thermal emission of 76 brown dwarfs,
substellar companions, and hot Jupiters. All our spectra have been acquired with the Hubble Space Telescope's Wide
Field Camera 3 instrument and its G141 grism The near-infrared derived spectral types of these objects range from
L4 to Y1. This sample also includes two very low surface gravity objects and ve intermediate-surface-gravity objects.
Eight of our targets have estimated masses below the deuterium-burning limit, some as low as 2 MJup.
We also provide a thoughtful analysis of the database. Spectral indices designed to search for composite atmosphere
brown dwarfs indicate that eight objects in our sample are strong candidates to have such atmospheres. In addition,
none are overluminous, therefore their composite atmospheres are unlikely a companion-induced artifact. Five of the
eight conrmed candidates have been reported as photometrically variable, suggesting that composite atmospheric
indices are useful in identifying brown dwarfs with strongly heterogeneous cloud covers.
We measure the depths of the H2O and CH4 bands at 1.4 and 1.2 m, respectively, and derive a relation between
near-infrared spectral types and band depths that are useful in classifying spectral types of brown dwarfs.
Finally, we compare hot Jupiters, other planetary mass objects, and brown dwarfs in a near-infrared color-magnitude
diagram. We conrm that the coldest hot Jupiters in our sample have spectra similar to mid-L dwarfs,
and the hottest hot Jupiters have spectra similar to those of M-dwarfs. Our sample provides a very highquality,
uniform dataset of a broad range of ultracool atmospheres, allowing large-scale, comparative studies, as well
providing HST legacy spectral library.