1. Spectroscopic Analysis of the mid-IR excesses of WDs Jana Bilikova 1 You-Hua Chu 1, Kate Su 2, Robert Gruendl 1, et al. 1 U. of Illinois at Urbana-Champaign, 2 U. of Arizona

2. Spitzer MIPS 24 μm Survey of Hot WDs WD Name PN T eff (kK) F 24 (mJy) L IR /L * K1-22 K1-22 141 1.07 3.1 E-5 NGC 2438 NGC 2438 114 12.4 4.5 E-4 WD 0103+732EGB 1 150 2.76 1.3 E-5 WD 0109+111 110 0.27 4.9 E-6 WD 0127+581 Sh2-188 102 0.34 2.7 E-5 WD 0439+466Sh2-216 95 0.98 3.7 E-6 WD 0726+133Abell 21 130 0.92 1.6 E-5 WD 0950+139 EGB 6 110 11.7 2.6 E-4 WD 1342+443 79 0.22 4.0 E-5 WD 2226-210Helix 110 48.0 2.5 E-4

3. Spitzer Archival search Serch for CSPNs with IR excess 60 PNe examined 18 photometry carried out 6 show IR excess: NGC 6804, NGC 7139 NGC 2438, NGC 2346, NGC 6853, NGC 6905

4. Mid-IR emission of hot WDs

5. Possible Origins of IR Excesses Collisions of KBOs Binary evolution Compact nebulosity in born-again PNe

6. 6 KPNO Echelle Spectra [OIII] HαHα Abell 30 NGC 2438 EGB 6 EGB 1 H-poor: feature in [OIII] does not show up in Hα All [OIII] features show H α counterparts Can eliminate the compact H-poor nebulosity scenario

7. Our dust disk model Optically thin Dust grains - silicates/amorphous carbon - sizes: n(a) ~ a -3.5 - a min set by β=F rad /F g of 0.5 (Artymowicz & Clampin 1997) - Q abs from Mie theory Uniform surface density

8. WD 0439+466 The closest CSPN Sh2-216 D=129 pc (Harris et al. 2007) 8 40’’ 5’

9. Sh 2-216 model T eff = 95,000 K log g = 6.9 M = 0.55 M  L = 160 L  (Rauch et al. 2007) T eff = 95,000 K log g = 6.9 M = 0.55 M  L = 160 L  (Rauch et al. 2007) a min ~ 40-80 um R ~ 60-100 AU M = 0.001 Mearth a min ~ 40-80 um R ~ 60-100 AU M = 0.001 Mearth

10. CSPN K1-22 40’’ 2’’ HST has resolved a companion at 0.35’’ (~450 AU) from the CSPN (Ciardullo 1999). D = 1.33 kpc (Ciardullo 1999)

11. CSPN K1-22 model T eff = 141,000 K log g = 6.73 M = 0.59 M  (Rauch et al. 1999) L = 325 L  (phot) T eff = 141,000 K log g = 6.73 M = 0.59 M  (Rauch et al. 1999) L = 325 L  (phot) Kurucz model atm. T eff = 5,000 K M0V star Kurucz model atm. T eff = 5,000 K M0V star a min ~ 250 um R ~ sublim - 40 AU M = 0.002 Mearth a min ~ 250 um R ~ sublim - 40 AU M = 0.002 Mearth [O IV] [Ne III]

12. WD 0103+732 Distance = 650 pc (Napiwotzki 2001)

13. WD 0103+732 model T eff = 147,000 K log g = 7.34 M = 0.65 M  (Napiwotzki 2001) L = 480 L  (phot) T eff = 147,000 K log g = 7.34 M = 0.65 M  (Napiwotzki 2001) L = 480 L  (phot) a min ~ 340 um R ~ 200 - 360 AU M = 0.14 Mearth a min ~ 340 um R ~ 200 - 360 AU M = 0.14 Mearth

14. Beware! Detailed spectral shape of the WD matters - model atmospheres have more UV emission  hotter grains  disk properties - e.g. WD 0103+732: ~480 Lsun, Rin ~ 200 AU ~1000 Lsun, Rin ~ 500 AU Distance matters - dist+phot  L WD  a min  disk properties - e.g. K1-22: d=1.33 kpc, L~300 Lsun d=3.4 kpc, L~1000 Lsun More complicatons

15. WD 0950+139 (EGB 6) Compact emission line source coincident with the CSPN (Fleming, Liebert, Green 1986) JHK excess (Fulbright & Liebert 1993) HST: A companion 0.18 ‘’ away (Bond 1994) IRAC, MIPS excess Featureless spectrum Su et al., in prep. KPNO echelle

16. CSPN NGC 6804 Spitzer MIPS 24 um Central emission line source Dust continuum, rising from J band We also see a silicate feature at 10 um. Gemini NIRI+Michelle

17. ORIGINS KBO collisions – Inner and outer edge (~100 AU) – Small dust mass (~0.1 Mearth) – Not too far for collisions (Dong et al.,Bonsor & Wyatt) Post-AGB binaries – Some CSPNs are binaries (maybe others hide a companion?) – CSPN stage right after post-AGB (do post-AGB binaries evolve into PNe?)

18. Conclusions Near and mid-IR excess is a good indicator of interesting phenomena Great variety among IR excesses – Near-IR excess only, mid-IR excess only, both – No emission lines, only emission lines, both – Featureless dust continuum, mineralogical features – Known companions, no companions Each needs to be studied in detail individually Stellar atmospheric models Stay tuned!