English: KOINTREAU-1b around XEST 17-036 (2MASS J04332621+2245293) with Keck. Figure 1 left part.

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 (PyWFS). We have found two faint (∆K∼7 mag), wide-separation companions to two ≈3-Myr-old Taurus members. Relative astrometry for these systems show that both companions are bound to their host stars. We obtained near-infrared spectra of these companions using IRTF/SpeX (R∼100) and Gemini/GNIRS (R∼1000-2000), and combine 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-IR 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+2.5−2.3 MJup, 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 magnitudes underluminous relative to other Taurus stars of the same spectral type. We detect exceptionally strong He I 1.083 μm 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.

Figure 1 caption:

Example Keck/NIRC2 signal-to-noise maps from our deep-exposure 10′′ K-band image stacks of each companion. These maps are computed by subtracting the mean and normalizing by the standard deviation in successive annuli around the host star. The companions are circled in green in each case. We note some electronic noise in the lower right quadrant of the shown epoch (December 2023) of KOINTREAU-2b data, but our measurements are unaffected by this.