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* †

Abstract

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 object separated by 1950 ± 200 au (40″) from a relatively close (2.17 ± 0.22 au, 0.″04) pair of and  objects. 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, ). 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.