Where Do Carbon-Carbon Bonds Originate ? The Peculiar Chemistry of the Oxygen-Rich Supergiant VY Canis Majoris

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Where Do Carbon-Carbon Bonds Originate ?The
Peculiar Chemistry of the Oxygen-Rich
Supergiant VY Canis Majoris

• L.M. Ziurys, A.J. Apponi, S.N. Milam, D.T Halfen,
  and N.J. Woolf

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Chemical Contribution of Circumstellar Envelopes

• Mass Loss from Cool, Evolved Stars
• - contributes 80 of mass to ISM
• - material from Asymptotic Giant Branch (AGB)
  stars
• - also from Red Supergiants (RSG)
• Mass Loss creates extensive Circumstellar
  Envelope
• - molecules form with an active chemistry
• - over 50 different chemical compounds
  observed
• Carbon-rich (C gt O) and Oxygen-rich (C lt O)
  envelopes
• - interstellar ratio is O/C 1.6 (C lt O)
• Carbon-rich appear to have a more complex
  chemistry
• - from observations of IRC10216 C-rich star
  150 pc away
• - exotic carbon-chains, silicon,
  metal-containing species

.
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Contribution of O-Rich Circumstellar Envelopes ?

• Molecules survive in outflows from circumstellar
  shells
• - Variety of species identified in planetary
  nebulae
• - Also in diffuse clouds (C3H2,CCH, H2S, H2CO)
• Circumstellar shells contributing to molecular
• content of ISM
• More O-rich than C-rich envelopes in ISM
• ? what is their molecular content,
  contribution ??
• Only limited observations in such objects
• - studies of AGB stars TXCam, IKTau, PPN
  OH231.8

Molecules in O-Rich Envelopes Molecules in O-Rich Envelopes Molecules in O-Rich Envelopes Molecules in O-Rich Envelopes
CO CS SiO H2O
OH HCN SiS SO
CN NH3 HNC SO2
But is this the complete answer ??
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The Interesting Case of VY Canis Majoris

• Morphology of VYCMa
• - Red Supergiant Star (M gt 15 M? )
• - evolving from main sequence to Type II SN
• - HIGH Mass Loss Rate 2 x 10-4 M? yr-1 (or
  1M? every 5000 yrs)
• - Cool (T 2800 K) but LUMINOUS ( 105 L?
  105 suns)
• - 1.5 kpc distant (IRC10216 150 pc)
• Well-known source of OH, H2O, SiO masers

VYCMa IR image/OH maser
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At first glance, chemically uninteresting CO,
HCN, SO,NH3
0
-5
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ARO Spectra-Line Survey of VYCMa

• Conducted at 1, 2, and 3 mm wavelengths
• - 200-275 GHz 130-170 GHz 65-115 GHz
• Observations with 12 m (2,3 mm) and SMT (ALMA
  Band 6 Rxr WH12)

Kitt Peak 12 m
SMT
Still alive and kicking, despite.
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Initial Results at the 12 m

• Spectrum of SiOJ3-2
• - Thermal profile
• - Nice simple outflow.
• But then..
• - HCO, J1-0 line ?
• - never conclusively
• detected in CSE (PN, PPN only)
• Asymmetric U-profile
• for SO, SO2
• ? Unusual molecules..
• ? Unusual line shapes

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More observations at SMT at 1 mm (ALMA mixer)..
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NaCl
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In VYCMa Profiles vary from species to
species Inner outflow and a disk OR MASERS ?
OH 1612 maser
In IRC10216 All spectra have same line widths,
general shape
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Initial Results of Survey
Molecules in VYCMa Molecules in VYCMa Molecules in VYCMa Molecules in VYCMa
H2O CO HCO SiO
SO2 CN HCN SiS
SO CS H2S PN
OH HNC NH3 NaCl

• Seven new species detected in VYCMa
• 16 molecules observed thus far
• Most chemically diverse O-rich Shell
• to date, including PPN OH231.8

• Five Carbon-Bearing Compounds other than CO
• ? CO NOT controlling chemistry in O-Rich Shell
• ? CO NOT controlling chemistry in C-Rich shell
  see Talk FC11
• No Kuiper-belt objects needed for O-Bearing
  species in IRC10216
• First metal-bearing species in O-rich shell
  NaCl
• First phosphorous-containing species in O-rich
  shell PN
• Line profiles indicate a complex source inner
  wind and outer disk
• ? Possible SO2, SO, CO masers
• ? grain condensation removing before terminal
  outflow velocity reached

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Conclusions and Future Directions

• Only about 20 of survey finished
• Likely to find other interesting species
• O-Rich shells can have a rich chemistry !
• More than just a simple spherical AGB wind
• O-rich shells important molecular
• contributors to ISM

Nick
Aldo
ACKNOWLEDGEMENTS NASA Astrobiology Nick
Woolf Stefanie Milam Aldo Apponi Staff of ARO
Stefanie
Introducing Emmy Tenenbaum FC11 ? More on C/O
chemistry in CSEs