Silica-Rich Bright Debris Disk around HD 15407A

We report an intriguing debris disk toward the F3V star HD 15407A in which an extremely large amount of warm fine dust (∼10−7M⊕) is detected. The dust temperature is derived as ∼500–600 K and the location of the debris dust is estimated as 0.6–1.0 AU from the central star, a terrestrial planet region. The fractional luminosity of the debris disk is ∼0.005, which is much larger than those predicted by steady-state models of the debris disk produced by planetesimal collisions. The mid-infrared spectrum obtained by Spitzer indicates the presence of abundant μm-sized silica dust, suggesting that the dust comes from the surface layer of differentiated large rocky bodies and might be trapped around the star.