ASTEROID BELTS IN DEBRIS DISK TWINS: VEGA AND FOMALHAUT

Abstract

Vega and Fomalhaut, are similar in terms of mass, ages, and global debris\ndisk properties; therefore, they are often referred as "debris disk twins". We\npresent Spitzer 10-35 um spectroscopic data centered at both stars, and\nidentify warm, unresolved excess emission in the close vicinity of Vega for the\nfirst time. The properties of the warm excess in Vega are further characterized\nwith ancillary photometry in the mid infrared and resolved images in the\nfar-infrared and submillimeter wavelengths. The Vega warm excess shares many\nsimilar properties with the one found around Fomalhaut. The emission shortward\nof ~30 um from both warm components is well described as a blackbody emission\nof ~170 K. Interestingly, two other systems, eps Eri and HR 8799, also show\nsuch an unresolved warm dust using the same approach. These warm components may\nbe analogous to the solar system's zodiacal dust cloud, but of far greater. The\ndust temperature and tentative detections in the submillimeter suggest the warm\nexcess arises from dust associated with a planetesimal ring located near the\nwater-frost line and presumably created by processes occurring at similar\nlocations in other debris systems as well. We also review the properties of the\n2 um hot excess around Vega and Fomalhaut, showing that the dust responsible\nfor the hot excess is not spatially associated with the dust we detected in the\nwarm belt. We suggest it may arise from hot nano grains trapped in the magnetic\nfield of the star. Finally, the separation between the warm and cold belt is\nrather large with an orbital ratio >~10 in all four systems. In light of the\ncurrent upper limits on the masses of planetary objects and the large gap, we\ndiscuss the possible implications for their underlying planetary architecture,\nand suggest that multiple, low-mass planets likely reside between the two belts\nin Vega and Fomalhaut.\n