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A Wide Planetary Mass Companion Discovered Through the Citizen Science Project Backyard Worlds: Planet 9

Presentation #102.224 in the session Poster Session.

Published onJun 20, 2022
A Wide Planetary Mass Companion Discovered Through the Citizen Science Project Backyard Worlds: Planet 9

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 arcsec 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 ~1sigma and our estimates for chance alignment yield a zero probability. Follow-up near infrared spectroscopy reveals W1243 to be a very red 2MASS (J-Ks=2.72), low-surface gravity source that we classify as L6–L8gamma. 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, the Gaia parallax along with the photometry and spectrum for W1243 we find a Teff=1303±31 K, logg=4.3±0.17 cm s2, and a mass of 15±5 MJup. We find a physical separation of ~1662 AU and a mass ratio of ~0.01 for this system. Placing it in context with the diverse collection of binary stars, brown dwarf and planetary companions, the BD+60 1417 system falls in a sparsely sampled area where the formation pathway is difficult to assess. Intriguingly, the host star had been observed by several direct imaging campaigns to no avail as they failed to zoom far enough out to find the companion.

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