Spitzer/IRAC Limits to Planetary Companions of Fomalhaut and epsilon Eridani

TL;DR

This study used Spitzer/IRAC infrared imaging to search for planetary companions around Fomalhaut and epsilon Eridani, setting new upper limits on their possible planet masses based on non-detections.

Contribution

First deep IRAC imaging observations of Fomalhaut and epsilon Eridani to constrain the presence of cool, Jupiter-like planets at specific orbital regions.

Findings

No planetary companions detected at Fomalhaut b's position with limits of 3 MJ.

Set upper mass limits of 4 MJ and <1 MJ around epsilon Eridani at different ring edges.

Results provide the strongest constraints to date on planets outside epsilon Eridani's debris ring.

Abstract

Fomalhaut and epsilon Eridani are two young, nearby stars that possess extended debris disks whose structures suggest the presence of perturbing planetary objects. With its high sensitivity and stable point spread function, Spitzer/IRAC is uniquely capable of detecting cool, Jupiter-like planetary companions whose peak emission is predicted to occur near 4.5 um. We report on deep IRAC imaging of these two stars, taken at 3.6 and 4.5 um using subarray mode and in all four channels in wider-field full array mode. Observations acquired at two different telescope roll angles allowed faint surrounding objects to be separated from the stellar diffraction pattern. No companion candidates were detected at the reported position of Fomalhaut b with 3 sigma model-dependent mass upper limits of 3 MJ (for an age of 200 Myr). Around epsilon Eridani we instead set a limit of 4 and <1 MJ (1 Gyr model age) at the inner and outer edge of the sub-millimeter debris ring, respectively. These results are consistent with non-detections in recent near-infrared imaging searches, and set the strongest limits to date on the presence of planets outside epsilon Eridani sub-millimeter ring.