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We present the discovery of CWISE J050626.96+073842.4 (CWISE J0506+0738), an L/T transition dwarf with extremely red near-infrared colors discovered through the Backyard Worlds: Planet 9 citizen science project. Photometry from UKIRT and CatWISE give a (J−K)_MKOcolor of 2.97 ± 0.03 mag and aJ_MKO− W2 color of 4.93 ± 0.02 mag, making CWISE J0506+0738 the reddest known free-floating L/T dwarf in both colors. We confirm the extremely red nature of CWISE J0506+0738 using Keck/NIRES near-infrared spectroscopy and establish that it is a low-gravity, late-type L/T transition dwarf. The spectrum of CWISE J0506+0738 shows possible signatures of CH₄absorption in its atmosphere, suggesting a colder effective temperature than other known, young, red L dwarfs. We assign a preliminary spectral type for this source of L8γ–T0γ. We tentatively find that CWISE J0506+0738 is variable at 3–5μm based on multiepoch WISE photometry. Proper motions derived from follow-up UKIRT observations combined with a radial velocity from our Keck/NIRES spectrum and a photometric distance estimate indicate a strong membership probability in theβPic moving group. A future parallax measurement will help to establish a more definitive moving group membership for this unusual object.

 

Abstract We have used data from the UKIRT Hemisphere Survey to search for substellar members of the Hyades cluster. Our search recovered several known substellar Hyades members, and two known brown dwarfs that we suggest may be members based on a new kinematic analysis. We uncovered thirteen new substellar Hyades candidates, and obtained near-infrared follow-up spectroscopy of each with IRTF/SpeX. Six candidates with spectral types between M7 and L0 are ruled out as potential members based on their photometric distances (≳100 pc). The remaining seven candidates, with spectral types between L5 and T4, are all potential Hyades members, with five showing strong membership probabilities based on BANYAN Σ and a convergent point analysis. Distances and radial velocities are still needed to confirm Hyades membership. If confirmed, these would be some of the lowest mass free-floating members of the Hyades yet known, with masses as low as ∼30 M Jup . An analysis of all known substellar Hyades candidates shows evidence that the full extent of the Hyades has yet to be probed for low-mass members, and more would likely be recovered with deeper photometric and astrometric investigations.