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 {11.6}_-1.0^+1.3 {M}_Jup} object separated by 1950 ± 200 au (40″) from a relatively close (2.17 ± 0.22 au, 0.″04) pair of {48}_-12⁺¹³ {M}_Jup} and {44}_-11⁺¹⁴ {M}_Jup} 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, {13.0}_-0.3^+0.4 {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.