The Formation and Evolution of Planetary Systems (FEPS): Discovery of an unusual debris system associated with HD 12039

We report the discovery of a debris system associated with the ∼30 Myr old G3/5V star HD 12039 using Spitzer Space Telescope observations from 3.6-160 μm. An observed infrared excess (L_IR/L* = 1 × 10 ^-4) above the expected photosphere for λ ≳ 14 μm is fit by thermally emitting material with a color temperature of T ∼ 110K, warmer than the majority of debris disks identified to date around Sun-like stars. The object is not detected at 70 μm with a 3 σ upper limit 6 times the expected photospheric flux. The spectrum of the infrared excess can be explained by warm, optically thin material comprised of blackbody-like grains of size ≳7 μm that reside in a belt orbiting the star at 4-6 AU. An alternate model dominated by smaller grains, near the blowout size a ∼ 0.5 μm, located at 30-40 AU is also possible but requires the dust to have been produced recently, since such small grains will be expelled from the system by radiation pressure in approximately a few times 10² yr.