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Stellar evolution
For low- and intermediate-mass stars, they
enter the red giant and subsequently, asymptotic giant branch (AGB) phases.
During the AGB, a star loses a significant
- f its initial main-sequence mass.
Evolution of gas and dust in AGB stars Kay Justtanont Chalmers - - PowerPoint PPT Presentation
Evolution of gas and dust in AGB stars Kay Justtanont Chalmers - - PowerPoint PPT Presentation
Evolution of gas and dust in AGB stars Kay Justtanont Chalmers University of Technology Stellar evolution For low- and intermediate-mass stars, they enter the red giant and subsequently, asymptotic giant branch (AGB) phases. During the
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As the star evolves off the AGB, fast winds develop
which impact on the AGB mass loss => shocks
The central star becomes hotter and ionize the CSE
around it => PDR.
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Molecules in CSEs
Since the photosphere is relatively cool,
molecules can form and ejected via the mass-loss process.
CSE environment also promote chemistry
due to the cool, dense and warm conditions in the inner CSE.
Molecules can be photodissociated in the
- uter part due to interstellar radiation
field.
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Molecules II
Molecules detected depend on the C/O ratio
- f the photosphere.
In M- (O-rich) stars , we observe H2O and
- ther oxides.
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R Dor – an O-rich CSE
Justtanont et al., 2012, A&A 537, A144
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Molecules II
Molecules detected depend on the C/O ratio
- f the photosphere.
In M- (O-rich) stars , we observe H2O and
- ther oxides.
In C-rich stars, we detect carboneceous
molecules, e.g., C2H2, HCN, … (H2O)
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HIFISTARS GTKP
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Molecules II
Molecules detected depend on the C/O ratio
- f the photosphere.
In M- (O-rich) stars , we observe H2O and
- ther oxides.
In C-rich stars, we detect carboneceous
molecules, e.g., C2H2, HCN, … (H2O)
In S-star (C/O ~ 1), both oxides and C-base
molecules have been seen.
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Schöier et al., 2011, A&A 530, A83
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Habing et al., 1994, A&A 286, 523
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IRC+10 216
C-star which is the brightest source at 5µm. At a distance of 120 pc (Schöier & Olofsson
2000), it is one of the nearest C-stars with moderately high mass-loss rate and shows remarkable inventory of molecules.
> 40 molecules have been detected, many
carbon chains but also metal salts and hydrides.
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Patel et al. 2011, ApJS 192, 17
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H2O in IRC+10216
Decin et al., 2010, Nature 467, 64
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Multiple shells seen in IRC+10216
Decin et al., 2011, A&A 534, 1
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Masers
Seen in O-rich CSEs Some transitions of OH, H2O, SiO can mase.
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OH masers are thought to be radiatively
pumped by the OH absorption doublet at 35 µm.
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From maser observations => magnetic field. High angular resolution observations of proper
motion of maser spots => distance
Amiri et al., 2011, A&A, in press
OH44.8-2.3
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Dusty circumstellar envelopes
The species of dust formed also reflect the
chemistry in the photosphere.
Oxides are formed in O-rich environment
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Sloan et al., 2011, ApJ 729, 121
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Silicate 10µm feature and mass-loss rate
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Dusty circumstellar envelopes
The species of dust formed also reflect the
chemistry in the photosphere.
Oxides are formed in O-rich environment Carbonaceous dust are observed in C-rich
stars.
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Speck et al., 2005, ApJ 634, 426
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Dusty circumstellar envelopes
The species of dust formed also reflect the
chemistry in the photosphere.
Oxides are formed in O-rich environment Carbonaceous dust are observed in C-rich
stars.
For S-stars, the dust is mainly oxides
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Water-ice in extreme OH/IR stars
Waters et al., 1996 A&A 315, L361 OH 32.8-0.3
Justtanont et al., 2006, A&A 450, 1051
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Crystalline silicates
OH 32.8-0.3 ISO-SWS
HD161796 Hoogzaad et al., 2002, A&A 389, 547
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Fosterite and enstatite in post-AGB stars
Molster et al., 2002, A&A 382, 241
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Fosterite (Mg2Sio4) in post-AGB stars
De Vries et al. 2011
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Waters et al., 1996, A&A 315, L361
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21µm feature in C-rich post-AGB stars
Justtanont et al., 1996, A&A 309, 612
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30µm feature in post-AGB stars : MgS
Hrivnak et al., 2009, ApJ 694, 1147
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PAHs in post-AGB stars and PNe
Beintema et al., 1996, A&A 315, L369
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Molecules in PPNe
SUCCESS - Hershel open-time program
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Bujarrabal et al., 2010 ,A&A 521, L3
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Bujarrabal et al., 2010, A&A 521, L3
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