A Wide Planetary Mass Companion Discovered through the Citizen Science Project Backyard Worlds: Planet 9
Debes, John H.; Gonzales, Eileen C.; Meisner, Aaron M.; Smart, R. L.; Kirkpatrick, J. Davy; Burgasser, Adam J.; Casewell, Sarah L.; Schneider, Adam C.; Marocco, Federico; Faherty, Jacqueline K.; Caselden, Dan; Kuchner, Marc J.; Gagné, Jonathan; Gerasimov, Roman; Aganze, Christian; Bardalez Gagliuffi, Daniella C.; Backyard Worlds: Planet 9 Collaboration; Rothermich, Austin; Vos, Johanna M.; Popinchalk, Mark; Hsu, Chih-Chun; Ayala, Andrew; Theissen, Christopher A.; Schümann, Jörg; Cooper, William J.
United States, Canada, United Kingdom, Italy
Abstract
Through the Backyard Worlds: Planet 9 citizen science project we discovered a late-type L dwarf co-moving with the young K0 star BD+60 1417 at a projected separation of 37″ or 1662 au. The secondary-CWISER J124332.12+600126.2 (W1243)-is detected in both the CatWISE2020 and 2MASS reject tables. The photometric distance and CatWISE proper motion both match that of the primary within ~1σ and our estimates for a chance alignment yield a zero probability. Follow-up near-infrared spectroscopy reveals W1243 to be a very red 2MASS (J-K s = 2.72), low surface gravity source that we classify as L6-L8γ. Its spectral morphology strongly resembles that of confirmed late-type L dwarfs in 10-150 Myr moving groups as well as that of planetary mass companions. The position on near- and mid-infrared color-magnitude diagrams indicates the source is redder and fainter than the field sequence, a telltale sign of an object with thick clouds and a complex atmosphere. For the primary we obtained new optical spectroscopy and analyzed all available literature information for youth indicators. We conclude that the Li I abundance, its loci on color-magnitude and color-color diagrams, and the rotation rate revealed in multiple TESS sectors are all consistent with an age of 50-150 Myr. Using our re-evaluated age of the primary and the Gaia parallax, along with the photometry and spectrum for W1243, we find T eff = 1303 ± 31 K, log g = 4.3 ± 0.17 cm s-2, and a mass of 15 ± 5 M Jup. We find a physical separation of ~1662 au and a mass ratio of ~0.01 for this system. Placing it in the context of the diverse collection of binary stars, brown dwarfs, and planetary companions, the BD+60 1417 system falls in a sparsely sampled area where the formation pathway is difficult to assess.