COol Companions ON Ultrawide orbiTS (COCONUTS) Results

First imaged exoplanet from the survey, COCONUTS-2 b, and I'm pretty sure that it's not going the only one.

The Second Discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) Program: A Cold Wide-Orbit Exoplanet around a Young Field M Dwarf at 10.9 pc

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We present the identification of the COCONUTS-2 system, composed of the M3 dwarf L 34-26 and the T9 dwarf WISEPA J075108.79-763449.6. Given their common proper motions and parallaxes, these two field objects constitute a physically bound pair with a projected separation of 594" (6471 au). The primary star COCONUTS-2A has strong stellar activity (Hα, X-ray, and UV emission) and is rapidly rotating (P_rot=2.83 days), from which we estimate an age of 150-800 Myr. Comparing equatorial rotational velocity derived from the TESS light curve to spectroscopic vsini, we find COCONUTS-2A has a nearly edge-on inclination. The wide exoplanet COCONUTS-2b has an effective temperature of T_eff=434±9 K, a surface gravity of logg=4.11^+0.11_-0.18 dex, and a mass of M=6.3^+1.5_-1.9 M_Jup based on hot-start evolutionary models, leading to a 0.016^+0.004_-0.005 mass ratio for the COCONUTS-2 system. COCONUTS-2b is the second coldest (after WD 0806-661B) and the second widest (after TYC 9486-927-1 b) exoplanet imaged to date. Comparison of COCONUTS-2b's infrared photometry with ultracool model atmospheres suggests the presence of both condensate clouds and non-equilibrium chemistry in its photosphere. Similar to 51 Eri b, COCONUTS-2b has a sufficiently low luminosity (log(L_bol/L_⊙)=-6.384±0.028 dex) to be consistent with the cold-start process that may form gas-giant (exo)planets, though its large separation means such formation would not have occurred in situ. Finally, at a distance of 10.9 pc, COCONUTS-2b is the nearest imaged exoplanet to Earth known to date.

*Update* Listed at EPE: http://exoplanet.eu/catalog/coconuts-2_b/

Previously brown dwarf COCONUTS-1 b had been imaged around white dwarf PSO J058.9855+45.4184:

COol Companions ON Ultrawide orbiTS (COCONUTS). I. A High-Gravity T4 Benchmark around an Old White Dwarf and A Re-Examination of the Surface-Gravity Dependence of the L/T Transition

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We present the first discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, a large-scale survey for wide-orbit planetary and substellar companions. We have discovered a co-moving system COCONUTS-1, composed of a hydrogen-dominated white dwarf (PSO J058.9855+45.4184; d=31.5 pc) and a T4 companion (PSO J058.9869+45.4296) at a 40.6′′ (1280 au) projected separation. We derive physical properties for COCONUTS-1B from (1) its near-infrared spectrum using cloudless Sonora atmospheric models, and (2) its luminosity and the white dwarf's age (7.3+2.8−1.6 Gyr) using Sonora evolutionary models. The two methods give consistent temperatures and radii, but atmospheric models infer a lower surface gravity and therefore an unphysically young age. Assuming evolutionary model parameters (T_eff=1255⁺⁶_-8 K, log g=5.44^+0.02_-0.03 dex, R=0.789^+0.011_-0.005 R_Jup), we find cloudless model atmospheres have brighter Y- and J-band fluxes than the data, suggesting condensate clouds have not fully dispersed around 1300 K. The W2 flux (4.6 μm) of COCONUTS-1B is fainter than models, suggesting non-equilibrium mixing of CO. To investigate the gravity dependence of the L/T transition, we compile all 60 known L6-T6 benchmarks and derive a homogeneous set of temperatures, surface gravities, and masses. As is well-known, young, low-gravity late-L dwarfs have significantly fainter, redder near-infrared photometry and ≈200-300 K cooler temperatures than old, high-gravity objects. Our sample now reveals such gravity dependence becomes weaker for T dwarfs, with young objects having comparable near-infrared photometry and ≈100 K cooler temperatures compared to old objects. Finally, we find that young objects have a larger amplitude J-band brightening than old objects, and also brighten at H band as they cross the L/T transition.

COol Companions ON Ultrawide orbiTS (COCONUTS). III. A Very Red L6 Benchmark Brown Dwarf around a Young M5 Dwarf

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We present the third discovery from the COol Companions ON Ultrawide orbiTS (COCONUTS) program, the COCONUTS-3 system, composed of a young M5 primary star UCAC4 374-046899 and a very red L6 dwarf WISEA J081322.19−152203.2. These two objects have a projected separation of 61′′ (1891 au) and are physically associated given their common proper motions and estimated distances. The primary star, COCONUTS-3A, has a mass of 0.123±0.006 M⊙ and we estimate its age as 100 Myr to 1 Gyr based on its kinematics and spectrophotometric properties. We derive its metallicity as 0.21±0.07 dex using empirical calibrations established by older higher-gravity M dwarfs and find this [Fe/H] could be slightly underestimated according to PHOENIX models given COCONUTS-3A's younger age. The companion, COCONUTS-3B, has a near-infrared spectral type of L6±1 INT-G, and we infer physical properties of T_eff=1362⁺⁴⁸_-73 K, log(g)=4.96^+0.15_-0.34 dex, R=1.03^+0.12_-0.06 R_Jup, and M=39⁺¹¹_-18 M_Jup, using its bolometric luminosity, its host star's age, and hot-start evolution models. We construct cloudy atmospheric model spectra at the evolution-based physical parameters and compare them to COCONUTS-3B's spectrophotometry. We find this companion possesses ample condensate clouds in its photosphere with the data-model discrepancies likely due to the models using an older version of the opacity database. Compared to field-age L6 dwarfs, COCONUTS-3B has fainter absolute magnitudes and a 120 K cooler Teff. Also, the J-K color of this companion is among the reddest for ultracool benchmarks with ages older than a few 100 Myr. COCONUTS-3 likely formed in the same fashion as stellar binaries given the companion-to-host mass ratio of 0.3 and represents a valuable benchmark to quantify the systematics of substellar model atmospheres.