The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE) (1108.4677v1)

Abstract: We present ground-based spectroscopic verification of six Y dwarfs (see Cushing et al), eighty-nine T dwarfs, eight L dwarfs, and one M dwarf identified by the Wide-field Infrared Survey Explorer (WISE). Eighty of these are cold brown dwarfs with spectral types greater than or equal to T6, six of which have been announced earlier in Mainzer et al and Burgasser et al. We present color-color and color-type diagrams showing the locus of M, L, T, and Y dwarfs in WISE color space. Near-infrared classifications as late as early Y are presented and objects with peculiar spectra are discussed. After deriving an absolute WISE 4.6 um (W2) magnitude vs. spectral type relation, we estimate spectrophotometric distances to our discoveries. We also use available astrometric measurements to provide preliminary trigonometric parallaxes to four our discoveries, which have types of L9 pec (red), T8, T9, and Y0; all of these lie within 10 pc of the Sun. The Y0 dwarf, WISE 1541-2250, is the closest at 2.8 (+1.3,-0.6) pc; if this 2.8 pc value persists after continued monitoring, WISE 1541-2250 will become the seventh closest stellar system to the Sun. Another ten objects, with types between T6 and >Y0, have spectrophotometric distance estimates also placing them within 10 pc. The closest of these, the T6 dwarf WISE 1506+7027, is believed to fall at a distance of roughly 4.9 pc. WISE multi-epoch positions supplemented with positional info primarily from Spitzer/IRAC allow us to calculate proper motions and tangential velocities for roughly one half of the new discoveries. This work represents the first step by WISE to complete a full-sky, volume-limited census of late-T and Y dwarfs. Using early results from this census, we present preliminary, lower limits to the space density of these objects and discuss constraints on both the functional form of the mass function and the low-mass limit of star formation.

• The paper confirms the identification and spectral classification of 100 brown dwarfs, including six Y dwarfs and eighty-nine T dwarfs, using ground-based spectroscopy.
• The research employs detailed color-color diagrams and near-infrared spectroscopy to refine spectral types and propose a new optical standard for T9 dwarfs.
• The study estimates spectrophotometric distances and analyzes space density, providing insights into star formation and the lower mass cutoff of the substellar mass function.

Overview of "The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)"

The paper "The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)" presents the spectral verification and photometric characteristics of brown dwarfs identified with data from the WISE mission. This document marks a significant cataloging effort of these sub-stellar objects, with a focus on establishing their physical and spectral properties.

Key Findings

• Discovery and Classification: The paper confirms the discovery of six Y dwarfs, eighty-nine T dwarfs, eight L dwarfs, and one M dwarf. These dwarfs were validated using ground-based spectroscopy. Importantly, the classification for objects ranging from $T0$ to $T9$ and extending to Y dwarfs showcases WISE's capability to identify very cold objects.
• Spectral and Photometric Analysis: The research provides extensive color-color and color-type diagrams that clearly position M, L, T, and Y dwarfs in the WISE color space. Near-infrared spectra for these discoveries aid in refining the classifications, even proposing a new optical standard for the T9 class.
• Distance Estimation and Galactic Distribution: Using a reliable absolute WISE magnitude versus spectral type relation, spectrophotometric distances were computed for all newly discovered objects. Preliminary trigonometric parallaxes are provided for four discoveries, indicating that several of these brown dwarfs are among the nearest known to the Sun.
• Implications on Space Density and Star Formation: The paper extends to examining the density and distribution of late-T and Y dwarfs, highlighting the significance of these findings in constraining the mass function's lower bounds and offering insights into star formation processes, suggesting a lower mass cutoff less than 10 Jupiter masses.

Implications and Future Directions

• Understanding Galactic Population: The extension to a full-sky, volume-limited brown dwarf census could refine our understanding of the spatial distribution and formation mechanisms of brown dwarfs across the galaxy.
• Contributions to Exoplanet Studies: Brown dwarfs serve as excellent proxies for studying planetary atmospheres, given their temperature similarity to giant exoplanets but without stellar contamination. Hence, the atmospheric model refinement through these observations could improve exoplanet characterizations.
• Infrared Astrophysics and Instrumentation: The WISE mission underscores the importance of infrared surveys for discovering cold, faint celestial bodies, prompting future missions to continue deep sky surveys at these wavelengths to reveal even cooler and fainter objects.

These findings represent a crucial step toward comprehensive mapping of the solar neighborhood's brown dwarfs, which potentially adjusts theoretical models in star and planet formation for subsequent studies.