64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009 Millimeter Detection of...
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Transcript of 64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009 Millimeter Detection of...
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
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
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
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
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 !
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)
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
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*
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 !
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)
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
64th International Symposium on Molecular Spectroscopy June 22 – 26, 2009
NSF Astronomy
NASA Astrobiology
Arizona
ObservatoryRadio
Arizona
ObservatoryRadio