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 $\sim 30$ Myrold G3/5V star HD 12039 using {\it Spitzer Space Telescope} observations from3.6 -- 160$\mu$m. An observed infrared excess (L$_{\rm IR}$/L$_{\ast} =1\times10^{-4}$) above the expected photosphere for $\lambda \gtrsim 14\mu$m isfit by thermally emitting material with a color temperature of T$\sim 110$ K,warmer than the majority of debris disks identified to date around Sun-likestars. The object is not detected at 70$\mu$m with a 3$\sigma$ upper limit 6times the expected photospheric flux. The spectrum of the infrared excess canbe explained by warm, optically thin material comprised of blackbody-likegrains of size $\gtrsim 7 \mu$m that reside in a belt orbiting the star at 4--6AU. An alternate model dominated by smaller grains, near the blow-out size$a\sim 0.5\mu$m, located at 30-40AU is also possible, but requires the dust tohave been produced recently since such small grains will be expelled from thesystem by radiation pressure in $\sim$ few $\times 10^{2}$yrs.Comment: 31 pages, 6 figures (poor quality bitmaps, but readable), accepted for publication in The Astrophysical Journa