Spitzer Surveys of IR Excesses of WDs Y.-H. Chu 1, R.A. Gruendl 1, J. Bilikova 1, A. Riddle 1, K. Su 2 1 Univ. of Illinois, 2 Univ. of Arizona Outline Where do we expect to see dust ? What wavelengths should we use ? What are the survey results ? What can we do in the future ? IR excesses can be used to diagnose low-mass companions, planets, and dust. Stellar Evolution White Dwarf Steffen & Schnberner (2006) Young WDs are hot and are surrounded by visible planetary nebulae. Stellar Evolution White Dwarf Star loses 50-80% of its mass Planetary system expands Dynamical rearrangement produces dust by 1. Tidal crushing of sub-planetary objects 1. Tidal crushing of sub-planetary objects: too close to star 2. Collisions among sub-planetary objects 2. Collisions among sub-planetary objects: resonance with giant planets raises density and collision rate Where do we expect to find dust around WDs? 1. Within the Roche Limit (< 0.01 AU) 2. Asteroid Belt at 3-5 AU 3. Kuiper Belt at AU Where do we expect to find dust around WDs? 1. Within the Roche Limit (< 0.01 AU) 2. Asteroid Belt at 3-5 AU 3. Kuiper Belt at AU Thermal equilibrium Energy absorbed = Energy emitted 4 R * 2 T * 4 ( r g 2 / 4 D 2 ) = 4 r g 2 T g 4 T g = T * ( R / 2D ) 0.5 max ~ 2900 m / T g Sublimation temperature ~ 1500 K Thermal equilibrium Energy absorbed = Energy emitted 4 R * 2 T * 4 ( r g 2 / 4 D 2 ) = 4 r g 2 T g 4 T g = T * ( R / 2D ) 0.5 max ~ 2900 m / T g Sublimation temperature ~ 1500 K Where do we expect to find dust around WDs? 1. Within the Roche Limit (< 0.01 AU) 2. Asteroid Belt at 3-5 AU 3. Kuiper Belt at AU Spitzer IRAC can detect these around WDs 30 AU, colliding KBOs? More combinations of WD T eff - survey are needed to probe the planetary systems Archives provide wonderful sources of data Spectroscopic observations are needed, and spectral analyses are essential Bilikovas talk