Mid-Infrared Spectra of Dust Debris around Main-Sequence Stars

We report spectra obtained with the Spitzer Space Telescope in the λ = 14-35 μm range of 19 nearby main-sequence stars with infrared excesses. The six stars with strong dust emission show no recognizable spectral features, suggesting that the bulk of the emitting particles have diameters larger than 10 μm. If the observed dust results from collisional grinding of larger solids, we infer minimum masses of the parent body population between 0.004 and 0.06 M⊕. We estimate grain production rates of ∼1010 g s-1 around λ Boo and HR 1570; selective accretion of this matter may help explain their peculiar surface abundances. There appear to be inner truncations in the dust clouds at 48, 11, 52, and 54 AU around HR 333, HR 506, HR 1082, and HR 3927, respectively.