Subarcsecond mid-ir structure of the dust shell around iras 22272+5435

We report sub-arcsecond imaging of extended mid-infrared emission from a proto-planetary nebula (PPN), \iras 22272+5435, performed at the MMT observatory with its newly upgraded 6.5 m aperture telescope and at the Keck observatory. The mid-infrared emission structure is resolved into two emission peaks separated by 0\arcsec.5 - 0\arcsec.6 in the MMT 11.7 \um image and in the Keck 7.9, 9.7, and 12.5 \um images, corroborating the predictions based on previous multi-wavelength morphological studies and radiative transfer calculations. The resolved images show that the PPN dust shell has a toroidal structure with the 0\arcsec.5 inner radius. In addition, an unresolved mid-IR excess appears at the nebula center. Radiative transfer model calculations suggest that the highly equatorially-enhanced (

\rho_{\rm eq}/\rho_{\rm pole} = 9

) structure of the PPN shell was generated by an axisymmetric superwind with

{\dot M}_{\rm sw} = 4 \times 10^{-6} M_{\odot}

yr

^{-1}

, which was preceded by a spherical asymptotic giant branch (AGB) wind with

{\dot M}_{\rm AGB} = 8 \times 10^{-7} M_{\odot}

yr

^{-1}

. These model calculations also indicate that the superwind shell contains larger dust grains than the AGB wind shell. The unresolved mid-infrared excess may have been produced by a post-AGB mass loss at a rate of

2 - 6 \times 10^{-7} M_{\odot}

yr

^{-1}

. While the central star left the AGB about 380 years ago after the termination of the superwind, the star seems to have been experiencing an ambient post-AGB mass loss with a sudden, increased mass ejection about 10 years ago.

References(61)

Figures(0)

- Astrophys.J.Suppl. 71 733

- Astrophys.J. 464 L195

- Astrophys.J. 365 L23

- Astrophys.J. 415 250

- Mon.Not.Roy.Astron.Soc. 276 715

- Astron.Astrophys.Suppl.Ser. 113 561

- Astrophys.J. 368 545

Mid-infrared (8-21) imaging of proto-planetary nebulae

et al.

- Astrophys.J. 492 (1998) 603
•
DOI:
- 10.1086/305051

- Astron.Astrophys. 223 227

- Astrophys.J. 528 841

- Astron.Astrophys.Suppl.Ser. 126 479

- Astrophys.J. 387 L89

- Astrophys.J. 290 L35

- Science 288 313

- Astron.Astrophys. 336 L41

- Nature 395 251

- Astron.J. 112 2064

- Astrophys.J. 438 341

- Astrophys.J. 371 631

- Astrophys.J. 420 783

- Astrophys.J. 513 421

- NOONE 250 1

Mass loss from carbon stars

M. Jura
(
- UCLA
)

- Astrophys.J. 303 (1986) 327-332
•
DOI:
- 10.1086/164077

- Astrophys.J. 434 713

The dying wind around hd 56126, a post-agb carbon star

- Astrophys.J.Lett. 544 (2000) L141
•
e-Print:
- astro-ph/0010038
•
DOI:
- 10.1086/317307

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1
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