Searching for Wide Companions and Identifying Circum(sub)stellar Disks through PSF-Fitting of Spitzer/IRAC Archival Data

The last decade has seen the discovery of a growing population of planetary-mass companions (~<20 M_Jup; hereafter PMCs) to young stars which are often still in the star-forming regions where they formed. These objects have been found at wide separations (>100 AU) from their host stars, challenging existing models of both star and planet formation. Demographic trends with mass and separation should distinguish between these formation models.

The extensive Spitzer/IRAC data set of every major star-forming region and association within 300 pc has great potential to be mined for wide companions to stars. I will present new results from my automated pipeline to find wide-orbit companions of stars via point spread function (PSF) subtraction in Spitzer/IRAC images. A Markov Chain Monte Carlo algorithm is the backbone of this PSF subtraction routine that efficiently creates and subtracts χ²-minimizing instrumental PSFs, measuring infrared photometry of the systems across the four IRAC channels (3.6 μm, 4.5 μm, 5.8 μm, and 8 μm). I will present a re-analysis of archival Spitzer/IRAC images of 11 young, low-mass (44 M_Jup-0.88 M_Sun; K3.5-M7.5) stars in 3 nearby star-forming regions (Chameleon, Taurus, and Upper Scorpius; d ~ 150 pc; τ ~ 1–10 Myr) known to host faint companions over a range of projected separations (1.7”-7.3”). I will discuss the characteristics of the systems found to have low-mass companions with non-zero [3.6] − [8.0] colors, including the confirmation of a ρ = 4.66” (540 AU), M = 20 M_Jup companion to [SCH06] J0359+2009, a young brown dwarf in Taurus.

My survey is sensitive to companions with masses approaching that of Jupiter at orbital radii of a few hundred AU, discovering wide PMCs in their birth environments and revealing their circum(sub)stellar disks. I will present my newest results in measuring the mid-IR photometry of substellar companions that have been directly imaged at optical or near-IR wavelengths and an automated companion search of all known young stars with existing Spitzer/IRAC data, concluding with my ongoing follow-up observations of candidate wide PMC systems with ground-based telescopes and the outlook for future observations with space-based telescopes.