The Hawaii Infrared Parallax Program. III. 2MASS J0249-0557 c: A Wide Planetary-mass Companion to a Low-mass Binary in the β Pic Moving Group

We have discovered a wide planetary-mass companion to the β Pic moving group member 2MASS J02495639-0557352 (M6 vl-g) using Canada-France-Hawaii Telescope/WIRCam astrometry from the Hawaii Infrared Parallax Program. In addition, Keck laser guide star adaptive optics aperture-masking interferometry shows that the host is itself a tight binary. Altogether, 2MASS J0249-0557ABc is a bound triple system with an 11.6^+1.3 _-1.0 M_jupobject separated by 1950 ±200 au (40″) from a relatively close (2.17 ±0.22 au, 0.″04) pair of 48⁺¹³ _-12 M_jupand 44⁺¹⁴ _-11 M_jupobjects. 2MASS J0249-0557AB is one of the few ultracool binaries to be discovered in a young moving group and the first confirmed in the β Pic moving group (22 ±6 Myr). The mass, absolute magnitudes, and spectral type of 2MASS J0249-0557 c (L2 vl-g) are remarkably similar to those of the planet β Pic b (L2, 13.0^+0.4 _-0.3 M_jup). We also find that the free-floating object 2MASS J2208+2921 (L3 vl-g) is another possible β Pic moving group member with colors and absolute magnitudes similar to β Pic b and 2MASS J0249-0557 c. β Pic b is the first directly imaged planet to have a "twin," namely an object of comparable properties in the same stellar association. Such directly imaged objects provide a unique opportunity to measure atmospheric composition, variability, and rotation across different pathways of assembling planetary-mass objects from the same natal material.