Chemistry of the First Hypervelocity Ultracool Subdwarf with Keck/NIRES

CWISE J124909.08+362116.0 is a hypervelocity ultracool subdwarf discovered in the Wide-field Infrared Survey Explorer (WISE) images by citizen scientists in the Backyard Worlds: Planet 9 program. At the estimated galactocentric velocity of 460±30 km/s and stellar mass of ~0.08 M☉, CWISE J1249+3621 is the lowest-mass hypervelocity star known. The origin of this object and its unusual kinematics remain uncertain. Using a follow-up observation of CWISE J1249+3621 with the Near-Infrared Echellette Spectrometer (NIRES) on the Keck II telescope and a grid of custom model atmospheres, we carried out a detailed chemical characterization of this object. In particular, we assessed the likelihood of CWISE J1249+3621 being an ejected member of a globular cluster. Large densities of stars in globular clusters provide suitable conditions for high-velocity scattering of low-mass members in three-body interactions. If the origin of CWISE J1249+3621 indeed lies in one of Milky Way globular clusters, this object may represent a large undiscovered population of chemically peculiar subdwarfs in the solar neighborhood. We also assess the possibility of CWISE J1249+3621 being a surviving companion to a Type 1a supernova. KSM.pdf is the digital poster presented at the conference. lightning_slide.pdf is the slide used for the one-minute lightning talk advertising the poster.