64th international symposium on molecular spectroscopy june 22 – 26, 2009 millimeter detection of...
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
Millimeter Detection of AlO (X2Σ+): Metal Oxide Chemistry in the Envelope
of VY Canis Majoris
E.D. Tenenbaum and L.M. ZiurysDepartment of ChemistryDepartment of Astronomy
Arizona Radio Observatory, Steward ObservatoryUniversity of Arizona
Arizona
ObservatoryRadio
Arizona
ObservatoryRadio
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
Small Number Statistics and Interstellar Chemistry• Over 140 interstellar molecules (and similar number of chemical models)• Only a handful of astronomical sources carefully studied
Are we “missing” sources with different chemistry ???
• Circumstellar Material: C-Rich shells principally observed (IRC+10216)• Oxygen-rich shells neglected• A closer look at O-rich envelopes
Circumstellar gas of O-rich Supergiant Star
VY Canis Majoris (VY CMa)• Spectral Line survey in 1 mm band (210 – 285 GHz)• First comprehensive study of
O-rich circumstellar environment• Observed IRC+10216 for comparison
10 "
Envelope of VY CMa
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
Prime Time at the ARO Submillimeter Telescope
Arizona
ObservatoryRadio
Arizona
ObservatoryRadio
• Arizona Radio Observatory (ARO) operates:
- Submillimeter Telescope (SMT)
-12 m at Kitt Peak• Installed new 1 mm receiver at SMT• Utilizes ALMA Band 6 mixers• Achieve noise levels of 3 mK ( 1 sigma)
12 m SMT
1 mm insert
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
• Collected data in 1 GHz sections• 3 year project using over 2000 hours in telescope time
ARO 1 mmSurvey ofVY CMa andIRC+10216
PhD ThesisE.Tenenbaum
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
RAW Data: SMT at 1 mm
• No baseline
subtraction• No smoothing• No other
manipulations• 30 hours
integration
AlO: N = 7→ 6
H2O maser
7 years ofwork atthe SMT….but look at theSpectra !
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
Observations of AlO (X2Σ+)• Two 1 mm transitions: N = 7 → 6 and
N = 6 → 5 at 267.9 and 229.6 GHz• Observed with SMT• One 2 mm line measured with the 12 m
at 153 GHz (N = 4 → 3)• Different line profiles
Al hyperfine structure: varies with
frequency
Free radical
Lab spectrumfromYamada et al.(1990)
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
..............
5"
Arc I
Arc II
CNT
(Ziurys et al. 2007 Nature)
VY CMa: Complex Source
• Spherical wind
- inner flow with
narrow linewidths
- outer flow with
full expansion
velocity • Blue/Red-shifted
outflows
blue red
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
Line Parameters of Observed AlO Transitions
Transition ν (MHz) Θb VLSR (km/s) TA* (mK)
N = 76 267937 28 25 ± 5 7 ± 2
N = 65 229670 33 25 ± 6 3 ± 1
N = 43 153124 41 27 ± 6 1.4 ± 0.5
AlO
Ntot ~ 2 × 1015 cm-2
Trot ~ 230 K
f (AlO/H2) ~ 10-8
• Linewidths of ~ 10 - 15 km/s
Accounts for HF components in profiles
• Identical to NaCl: θs ~ 0.5“
• Inner part of spherical flow at r ~ 30 R*
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
12 13 14 15 16 17 18 19Log r (cm)
R*
R1
Star
Dust Shell Acceleration Zone
Vexp ~ 15 km s-1T ~ 1000 K1010 cm-3
T ~ 25 K105 cm-3
UV
UV
UV
• Molecules created at LTE near stellar photosphere (T ~ 1000 -2000 K)
• For AlO (r ~ 30 R*): near photosphere
Implications for Circumstellar Chemistry
ObservedAbundanceof AlO
But AlOHAnd Al2OMoreAbundant !
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
And Even More Aluminum… • AlOH also identified in VY CMa• Emission weaker than AlO
More than LTE chemistry• Shocks disrupt condensation process
into Al2O3
Lab spectrum from 1993 (Apponi, Barclay and Ziurys)
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
• 20 molecules in VY CMa (OH, NH3)
• Spectrum dominated by SO2, SiO, SiS
• What else ??
• New molecules in O-rich circumstellar gas: AlO, PO, AlOH• First time metal oxides and hydroxides seen in interstellar molecules• Oxygen-rich Circumstellar environment fosters different chemistry• Relate to grains, shocks, and photospheric molecules• Electronic Bands of AlO observed in stellar atmospheres
Conclusions and Future Directions
AlO: A → X
V4332 Sgr
CO CN CS HCN HCO+ HNC
SO2 SiS SiO NS H2S H2O
SO PN PO NaCl AlO AlOH
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64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
NSF Astronomy
NASA Astrobiology
Arizona
ObservatoryRadio
Arizona
ObservatoryRadio