CWISEP J193518.59$-$154620.3: An Extremely Cold Brown Dwarf in the Solar Neighborhood Discovered with CatWISE.

We present the discovery of an extremely cold, nearby brown dwarf in the solar neighborhood, found in the CatWISE catalog (Eisenhardt et al., in prep.). Photometric follow-up with Spitzer reveals that the object, CWISEP J193518.59-154620.3, has ch1$-$ch2 = 3.24$\,\pm\,$0.31 mag, making it one of the reddest brown dwarfs known. Using the Spitzer photometry and the polynomial relations from Kirkpatrick et al. (2019) we estimate an effective temperature in the $\sim$270--360 K range, and a distance estimate in the 5.6$-$10.9 pc range. We combined the WISE, NEOWISE, and Spitzer data to measure a proper motion of $\mu_\alpha \cos \delta = 337\pm69$ mas yr$^{-1}$, $\mu_\delta = -50\pm97$ mas yr$^{-1}$, which implies a relatively low tangential velocity in the range 7$-$22 km s$^{-1}$.