Spectroscopic Analysis of the mid-IR excesses of WDs

Jana Bilikova1 You-Hua Chu1, Kate Su2, Robert Gruendl1, et al.

1U. of Illinois at Urbana-Champaign, 2U. of Arizona

Spitzer MIPS 24 μm Survey of Hot WDs

WD Name PN Teff (kK) F24(mJy)

LIR/L*

K1-22 K1-22 141 1.07 3.1 E-5NGC 2438 NGC 2438 114 12.4 4.5 E-4WD 0103+732 EGB 1 150 2.76 1.3 E-5WD 0109+111 110 0.27 4.9 E-6WD 0127+581 Sh2-188 102 0.34 2.7 E-5WD 0439+466 Sh2-216 95 0.98 3.7 E-6WD 0726+133 Abell 21 130 0.92 1.6 E-5WD 0950+139 EGB 6 110 11.7 2.6 E-4WD 1342+443 79 0.22 4.0 E-5

WD 2226-210 Helix 110 48.0 2.5 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

KPNO Echelle Spectra

[OIII]

Hα

Abell 30

NGC 2438 EGB 6

EGB 1

• H-poor: feature in [OIII] does not show up in Hα • All [OIII] features show Hα counterparts• Can eliminate the compact H-poor nebulosity scenario

Our dust disk model

• Optically thin• Dust grains

- silicates/amorphous carbon- sizes: n(a) ~ a-3.5

- amin set by β=Frad/Fg of 0.5 (Artymowicz & Clampin 1997)

- Qabs from Mie theory• Uniform surface density

WD 0439+466

• The closest CSPN Sh2-216• D=129 pc (Harris et al. 2007)

8

40’’

5’

Sh 2-216 model

Teff = 95,000 Klog g = 6.9M = 0.55 ML = 160 L (Rauch et al. 2007)

amin ~ 40-80 umR ~ 60-100 AUM = 0.001 Mearth

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)

CSPN K1-22 model

Teff = 141,000 Klog g = 6.73M = 0.59 M(Rauch et al. 1999)

L = 325 L (phot)

Kurucz model atm.Teff = 5,000 KM0V star amin ~ 250 um

R ~ sublim - 40 AUM = 0.002 Mearth

[O IV]

[Ne III]

WD 0103+732

Distance = 650 pc (Napiwotzki 2001)

WD 0103+732 model

Teff = 147,000 Klog g = 7.34M = 0.65 M(Napiwotzki 2001)

L = 480 L (phot)

amin ~ 340 umR ~ 200 - 360 AUM = 0.14 Mearth

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 LWD amin disk properties - e.g. K1-22: d=1.33 kpc, L~300 Lsun d=3.4 kpc, L~1000 Lsun

• More complicatons

WD 0950+139 (EGB 6)

•Compact emission line source coincident withthe 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!