AKARI/IRC 18 μm survey of warm debris disks

Abstract

Context. Little is known about the properties of the warm (T dust ≳ 150 K) debris disk material located close to the central star, which has a more direct link to the formation of terrestrial planets than does the low-temperature debris dust that has been detected to date.Aims. To discover new warm debris disk candidates that show large 18 μm excess and estimate the fraction of stars with excess based on the AKARI/IRC Mid-Infrared All-Sky Survey data.Methods. We searched for point sources detected in the AKARI/IRC All-Sky Survey, which show a positional match with A-M dwarf stars in the Tycho-2 Spectral Type Catalogue and exhibit excess emission at 18 μm compared to what is expected from the K S magnitude in the 2MASS catalogue. Results. We find 24 warm debris candidates including 8 new candidates among A-K stars. The apparent debris disk frequency is estimated to be 2.8 ± 0.6%. We also find that A stars and solar-type FGK stars have different characteristics of the inner component of the identified debris disk candidates. While debris disks around A stars are cooler and consistent with steady-state evolutionary model of debris disks, those around FGK stars tend to be warmer and cannot be explained by the steady-state model.