Mass Loss and Structure of the Envelopes Around AGB and Post-AGB Stars Dinh Van Trung

Mass Loss and Structure of the envelopes around AGB and post-AGB stars Dinh Van Trung

Institute of Physics, Vietnamese Academy of Science and Technology

Jeremy Lim Sebastien Muller Katat Wong Sun Kwok  Intermediate mass stars (1 Msun to 8 Msun) evolve through Asymptotic Giant Branch (AGB) and eventually become Planetary Nebulae (PN)

 Mass loss during the AGB phase: 10−7 to 10−4 Msun/yr Schematic view of the circumstellar envelope

Le Bertre (2007) Some properties of envelope around AGB stars

• Wind driven by radiation pressure on dust particles • Envelopes are roughly spherically symmetric • Contains large amount of both dust and gas • Strong in molecular emissions • Active chemistry with many different molecules detected Castro- Carrizo et al. (2010) Post-AGB stars

• Central stars become hotter • Bipolar or multi-polar structures • Collimated high velocity outflows

Egg nebula observed with HST (Sahai et al. 1998) HCN J=3-2 emission in W Hya

W Hya is the closest O-rich envelope (distance ~70 pc)

Centrally peaked HCN J=3—2 emission means HCN is formed via shock-chemistry in the inner envelope. Small velocity gradient: weak bipolar outflow or presence of rotation in the envelope

Model: velocity law ~ Log10(r), slow acceleration !!! More recent SiO J=8 – 7 with the SMA

Dinh-V-Trung et al. in preparation Observed and Modeled Profile for SiO J=8 – 7 Cyanopolyyne emission in C-rich envelope IRC+10216

HC3N J = 5 – 4

HC5N J = 16 – 15

HC5N J = 9 – 8 The arcs or incomplete shells represent mass loss enhancement episode and cover above 10% of stellar surface at the time of ejection.

Hollow shell structure is roughly consistent with current chemical models

Cherchnef & Glassgold (1993) Chemical pathways to form cyanopolyynes

HC5N / HC3N in IRC+10216

Cherchnef & Glassgold (1993)

Distributions of cyanopolyynes are spatially coincident.

Need to consider different ways to form cyanopolyynes or need to include structures of envelope. Cyanopolyynes in other C-rich AGB stars

Lp And CRL 2155

Dinh-V-Trung et al. in preparation HC3N in another C-rich envelope CIT 6 Dinh-V-Trung & Lim (2009)

• A nearly spherical thin outer shell + inner one-arm spiral • HC3N is present near the central AGB star ! Spiral pattern produced by a binary companion to AGB star

Mastrodemos & Morris (1999) Recent eVLA observations by Claussen et al. (2011)

Many arcs but no clear spiral !!! Spiral model of HC3N data (Kim et al. 2013) Post-AGB stars: probing the envelope of Egg nebula

CO J= 2--1 emission observed with PdBI (Cox et al. 2000)

HST image of Egg nebula (Sahai et al. 1998) Current popular model: a binary companion may produce high velocity jet and expanding torus

Morris (1987)

HC3N J=5--4 emission in the Egg nebula

Dinh-V-Trung & Lim (2009)

• HC3N shell roughly spherically symmetric is punctured at the location of the high velocity jets.

• HC3N is also present at the center of the nebula. This is not predicted with current photochemistry model. Channel maps of HC3N J=5—4 emission obtained with VLA.

Model Dust continuum emission at 43 GHz

Multiple companions to the post-AGB star in the Egg ??? Pole - on view Side - on view

Mastrodemos & Morris (1998) Kim & Taam (2012) Yellow hypergiant IRC+10420

Very strong IR excess Distance: 5 kpcs (uncertain)

Luminosity: 6 x 105 Lsun -4 Mass loss rate: up to 10 Msun/yr Spectral type variation: late F  mid A Warmest OH maser source !

Within 2 “ – jet-like structures, rays, small nearly spherical shells or arcs are evidence for high mass loss ejections in the past few hundred years. Tiffany et al. (2010) CO J=2-1 emission obtained with SMA at resolution ~ 1”

Dinh-V-Trung et al. (2009) eVLA data of SiO J=1-0 emission, a high density tracer (Katat Wong master thesis 2013, HKU) SiO J=2-1 emission obtained with PdBI (Castro-Carrizo et al. 2001) Big surprise ! Simple LVG calculations Non-Local calculation with spherical symmetry Single dish observations & model predictions for some SiO lines.

Summary

• Structure of circumstellar envelope is complex and can be influenced by several factors: mass loss anisotropy and variation, binary companion, high velocity jets

• Binary companion is probably quite common and influences the shaping of the envelope.

• Chemistry is closely related to the structure of envelope.

• Shock chemistry is likely to be important in addition to photochemistry.