Silica-Rich Bright Debris Disk around HD 15407A

We report an intriguing debris disk towards the F3V star HD 15407A, in which an extremely large amount of warm fine dust (~ 10^(-7) M_Earth) 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 micron-sized silica dust, suggesting that the dust comes from the surface layer of differentiated large rocky bodies and might be trapped around the star.