WISE J0830+2837: the first Y dwarf from Backyard Worlds: Planet 9

We present the discovery of WISE J083011.89+283658.23, the first Y dwarf identified via the Backyard Worlds: Planet 9 citizen science project. W0830 is a red, fast-moving source with a faint W2 detection and an upper limit in W1 photometry in multi-epoch AllWISE images. We have characterized this object with Hubble and Spitzer Space Telescope follow-up photometry. With mid-infrared detections in Spitzer's ch1 and ch2 and only upper limits in HST F105W and F125W filters, we find that this object has extremely red colors (ch1-ch2 = 3.252±0.233 mag, F125W-ch2 > 8.99 mag). We have obtained a parallax of 89.3/-13.9 mas from Spitzer observations, placing the source right outside the 10 pc sample. These colors are consistent with a Y1 source at T ~ 350 K, as extrapolated from the known Y dwarf population. We also present four additional Backyard Worlds: Planet 9 brown dwarf discoveries with estimated spectral types of T8-T9 within 30pc.