Structure of circumstellar envelope around AGB and post-AGB stars Dinh-V-Trung Sun Kwok, P.J. Chiu, M.Y. Wang, S. Muller, A. Lo, N. Hirano, M. Mariappan, J. Lim Institute of Astronomy and Astrophysics Academia Sinica

Introduction ● Intermediate mass stars (1 M  to 8 M  ) evolve through Asymptotic Giant Branch (AGB) and eventually become Planetary Nebulae (PN) ● Mass loss during the AGB phase: 10  7 to 10  4 M  /yr Shaping must occur either at the end of AGB phase or during the short transition stage (proto-planetary nebula PPN). Morphology of envelope AGB phase: spherically symmetric PN phase: wide variety of shapes PPN phase: Bipolar more common

Program to study the structure of envelopes with the Sub-millimeter Array IRC CIT 6 R Scl V Hya Pi Gru IRC VY CMa IRAS NGC 7027

Envelope around AGB stars is commonly assumed to be spherically symmetric & homogeneous. But in reality the envelope is complicated & interesting ! 1.3 mm dust continuum emission in IRC V - band Groenewegen et al. (1997) Maurron & Huggins (1999)

VLA data of HC 5 N J=9  8 at 23 GHz. Synthesized beam ~ 4 arcsec. Lucas & Guelin (1999) IRC+10216

SMA CO J=2  1 emission from R Scl Detached shell !

Detached shell: V exp ~ 15 km/s Present day wind: V exp ~ 10 km/s Dynamical age ~ 1700 yr Helium flash ? CO J=2  1

 Gru CO J=2-1 emission Poster by Chiu et al Disk & high velocity outflow are present in envelope of a normal AGB star.

Molecular emission from V Hya Poster by Hirano et al Disk & collimated high velocity outflow are present

Mid-IR image (Kwok et al. 2002) BIMA CO J=1  0 image 21  m Proto-Planetary nebula IRAS Meixner et al. (2004)

IRAS CO J=3-2  ~ 2 arcsec.

CO J=3-2 emission superposed on Mid-IR image at 18  m.

AGB wind Torus To observer North Schematic view of IRAS

Model parameters for IRAS ● Expansion velocity of the wind : 10 km/s ● Outer spherical AGB wind with mass loss M  /yr ● Axi-symmetric torus with mass loss ~ M  /yr ● Inner radius of torus ~ cm or 1500 yrs in dynamical age ● Outer radius of torus ~ cm or 2000 yrs in dynamical age ● Envelope is viewed at 45 degrees from below the equator

CO J=3-2 observation – channel maps Model channel maps

Brightest planetary nebula at all wavelengths Distance ~ 900 pc Central white dwarf T * ~ K Young HII region surrounded by massive molecular envelope. Rich in molecular lines and carbon chemistry NGC 7027

HST optical images in H , OIII & NII. HST near IR images

@230 GHz Beam : 2.65’’ x 1.52’’ (77°) Total flux : ~ 3.6 Jy JCMT : 3.8  0.2 Jy (Knapp et al. 345 GHz Beam : 1.71’’ x 0.85’’ (73°) Total flux : ~ 1.45 Jy CONTINUUM

12 CO J=2-1

Integrated intensity 12 CO(2-1) and 1.3 mm continuum

Future work Combine SMA & single dish (JCMT, CSO, HHT) data recover short spacing flux Multi-line observations & molecular excitation physical conditions Effects of high velocity outflow on circumstellar envelope radiation hydrodynamics Better understanding of the physics of circumstellar envelopes.

Scattered light polarizationCO J=2  1 R Scl

Histogram: CO J=3-2 from HHT 10m telescope Red solid line: CO J=3-2 profile predicted by model

CO J=3-2 & continuum