ASpitzerIRAC Search for Substellar Companions of the Debris Disk Star ε Eridani

We have used the InfraRed Array Camera (IRAC) onboard the Spitzer Spacetelescope to search for low mass companions of the nearby debris disk starepsilon Eridani. The star was observed in two epochs 39 days apart, withdifferent focal plane rotation to allow the subtraction of the instrumentalPoint Spread Function, achieving a maximum sensitivity of 0.01 MJy/sr at 3.6and 4.5 um, and 0.05 MJy/sr at 5.8 and 8.0 um. This sensitivity is notsufficient to directly detect scattered or thermal radiation from the epsilonEridani debris disk. It is however sufficient to allow the detection of Jovianplanets with mass as low as 1 MJ in the IRAC 4.5 um band. In this band, wedetected over 460 sources within the 5.70 arcmin field of view of our images.To test if any of these sources could be a low mass companion to epsilonEridani, we have compared their colors and magnitudes with models andphotometry of low mass objects. Of the sources detected in at least two IRACbands, none fall into the range of mid-IR color and luminosity expected forcool, 1 Gyr substellar and planetary mass companions of epsilon Eridani, asdetermined by both models and observations of field M, L and T dwarf. Weidentify three new sources which have detections at 4.5 um only, the lowerlimit placed on their [3.6]-[4.5] color consistent with models of planetarymass objects. Their nature cannot be established with the currently availabledata and a new observation at a later epoch will be needed to measure theirproper motion, in order to determine if they are physically associated toepsilon Eridani.Comment: 36 pages, to be published on The Astrophysical Journal, vol. 647, August 200