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

Spitzer MIPS 24 μm Survey of Hot WDs WD Name PN T eff (kK) F 24 (mJy) L IR /L * K1-22 K E-5 NGC 2438 NGC E-4 WD EGB E-5 WD E-6 WD Sh E-5 WD Sh E-6 WD Abell E-5 WD EGB E-4 WD E-5 WD Helix E-4

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

Mid-IR emission of hot WDs

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

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

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

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

Sh 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 ~ um R ~ AU M = Mearth a min ~ um R ~ AU M = Mearth

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

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 = Mearth a min ~ 250 um R ~ sublim - 40 AU M = Mearth [O IV] [Ne III]

WD Distance = 650 pc (Napiwotzki 2001)

WD 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 ~ AU M = 0.14 Mearth a min ~ 340 um R ~ AU M = 0.14 Mearth

Beware! Detailed spectral shape of the WD matters - model atmospheres have more UV emission  hotter grains  disk properties - e.g. WD : ~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

WD (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

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

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?)

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!