Keck Observations in the INfrared of Taurus and ρ Oph Exoplanets And Ultracool Dwarfs (KOINTREAU) I: A Planetary-mass Companion and a Disk-obscured Stellar Companion Discovered in Taurus

Abstract We present the first discoveries from Keck Observations in the Infrared of Taurus and ρ Oph Exoplanets and Ultracool dwarfs (KOINTREAU), an adaptive optics imaging survey of young stars in the Taurus and ρ Oph star-forming regions using the Keck infrared pyramid wavefront sensor. We have found two faint (Δ K ∼7 mag), wide-separation companions to two ≈3 Myr old Taurus members. Relative astrometry for these systems shows that both companions are bound to their host stars. We obtained near-infrared spectra of these companions using the Infrared Telescope Facility/SpeX ( R ∼100) and the Gemini North InfraRed Spectrograph (Gemini/GNIRS; R ∼ 1000–2000), and combined these with photometry from our NIRC2 imaging, the Pan-STARRS survey, and Spitzer/IRAC archival imaging to constrain their properties. One companion, KOINTREAU-1b (at a projected separation of 690 au), has an average near-infrared spectral type of M9 ± 2, a gravity classification of vl-g , and a changing spectral type between the SpeX (M7) and GNIRS (L1) observations. We estimate this object’s mass to be 10 . 6 − 2.3 + 2.5 M Jup , making KOINTREAU-1b the fifth planetary-mass companion found in Taurus. The other companion, KOINTREAU-2b (projected separation 560 au), has a spectral type of M4.5 ± 1 but is ≈4 mag underluminous relative to other Taurus stars of the same spectral type. We detect exceptionally strong He I 1.083 μ m emission from this object, indicative of outflows driven by ongoing accretion, but with a conspicuous lack of accompanying H emission. We conclude that KOINTREAU-2b is a young star obscured by an edge-on disk and observed in scattered light. Finally, we derive a distortion solution for NIRC2 imaging, which shows a 0 . ° 118 difference in position angle from the previous distortion solution.