A Mid-Infrared Study of Directly-Imaged Planetary-Mass Companions using Archival Spitzer/IRAC Images

Abstract

The atmospheres and accretion disks of planetary-mass and substellar companions provide an unprecedented look into planet and moon formation processes, most notably the frequency and lifetime of circumplanetary disks. In our ongoing effort to leverage the extraordinary sensitivity of the Spitzer /Infrared Array Camera (IRAC) at 3.6, 4.5, 5.8, and 8.0 µm to study wide planetary-mass and substellar companions near the diffraction limit, we present point-spread function (PSF) fitting photometry of archival Spitzer /IRAC images for nine stars (G0 to M4+M7) in nearby star-forming regions or stellar associations that host companions at separations of ρ = 1. 17 − 12. 33. We detect all system primaries in all four IRAC channels and recover eight low-mass companions in at least one IRAC channel for our sample, five of which have not been resolved previously in IRAC images. We measure non-photospheric [3.6] − [8.0] colors for four of the system companions (DH Tau B, 2M0441 B, SR 12 c, ROXs 42B b), confirming or discovering the presence of circumstellar or circum(sub)stellar disks. We detect fluxes consistent with photospheric emission for four other companions (AB Pic b, CHXR 73 b, 1RXS J1609 b, HD 203030 b) that are unlikely to host disks. Combined with past detections of accretion or disk indicators, we determine the global disk frequency of young (<15 Myr) wide companions with masses near the deuterium-burning limit to be 56% ± 12%.