The complete census of 70 μm-bright debris disks within "the formation and evolution of planetary systems" Spitzer legacy survey of sun-like stars

Abstract

We report detection of cool dust surrounding solar-type stars from observations performed as part of the Spitzer Legacy Science Program FEPS. From a sample of 328 stars having ages ~0.003-3 Gyr we have selected sources with 70 μm flux densities indicating excess in their SEDs above expected photospheric emission. Six strong excess sources are likely primordial circumstellar disks, remnants of the star formation process. Another 25 sources having ≥3 σ excesses are associated with dusty debris disks, generated by collisions within planetesimal belts that are possibly stirred by existing planets. Six additional sources with ≥2 σ excesses require confirmation as debris disks. In our analysis, most (>80%) 70 μm excess sources have ≥3 σ excesses at 33 μm as well, while only a minority (<40%) have ≥3 σ excesses at 24 μm. The rising SEDs toward (and perhaps beyond) 70 μm imply dust temperatures < 45–85 K for debris in equilibrium with the stellar radiation field. From fitted single-temperature blackbody models we infer bulk dust properties such as characteristic temperature, location, fractional luminosity, and mass. For >1/3 of the debris sources we find that multiple temperature components are suggested, implying a dust distribution extending over many tens of AU. Because the disks are dominated by collisional processes, the parent body (planetesimal) belts may be extended as well. Preliminary assessment of the statistics of cold debris around Sun-like stars shows that ~10% of FEPS targets with masses between 0.6 and 1.8 M☉ and ages between 30 Myr and 3 Gyr exhibit excess 70 μm emission. We find that fractional excess amplitudes appear higher for younger stars and that there may be a trend in 70 μm excess frequency with stellar mass.

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