hco + in the helix nebula
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HCO + in the Helix Nebula. Lindsay N. Zack Lucy M. Ziurys Department of Chemistry Department of Astronomy Steward Observatory Arizona Radio Observatory University of Arizona. Planetary Nebulae. - PowerPoint PPT PresentationTRANSCRIPT
June 25, 200964th International Symposium on Molecular Spectroscopy
Lindsay N. ZackLucy M. Ziurys Department of Chemistry Department of Astronomy Steward Observatory Arizona Radio Observatory University of Arizona
HCO+ in the Helix Nebula
June 25, 200964th International Symposium on Molecular Spectroscopy
Planetary Nebulae• Glowing shell of gas and plasma
formed by low to intermediate mass stars in their final stage of evolution
• Strong UV radiation field from central star
• Shapes and sizes vary
June 25, 200964th International Symposium on Molecular Spectroscopy
Chemistry in Planetary Nebulae• Strong UV field should destroy molecules
in PNe• Several molecules have been detected in
young PNe• Primarily ions and radicals• Survival in clumps of gas and dust?
Molecules Identified in PNe
CO CN CCH N2H+
HCN CH H2 CH+
HNC OH HCO+ H2O
H2CO C2H2 CO+ N2H+
CS C2H C3H2 SiS Tenenbaum et al., in preparation
June 25, 200964th International Symposium on Molecular Spectroscopy
The Helix Nebula
Age: ~12,000 yearsDistance: ~200 pcAngular Size: ~1000”
• Very old• Lots of dust and gas
• Atomic gas : H, N II, O I, C I• Molecular gas: CO and vibrationally
excited H2
• Interesting structure• Cometary globules
June 25, 200964th International Symposium on Molecular Spectroscopy
CO (J = 2-1) Map of the Helix
Young et al. 1999
Multiple Velocity Components
June 25, 200964th International Symposium on Molecular Spectroscopy
Why HCO+ ?• = 3.89 D• High critical density (ncr ~ 105 cm-3) indicates that
HCO+ emission is present in dense gas around the Helix– CO: = 0.11 D; ncr ~ 103 cm-3
• Dense gas is shielding and can preserve molecules
June 25, 200964th International Symposium on Molecular Spectroscopy
Mapping the Helix in HCO+
Goals…• Complete a fully sampled map in HCO+ (J = 1-0)• Identify “new” clumps of dense gas that may be chemically
interesting• Examine the kinematic structure of the Helix• Determine density and temperature distributions• Model HCO+ densities with LVG analysis• Examine chemistry of old PN in detail
June 25, 200964th International Symposium on Molecular Spectroscopy
HCO+ Observations• ARO 12m on Kitt Peak• HCO+ (J = 1-0) 89.18853 GHz• Optimal project for new ALMA-
type Band 3 receiver– Tsys < 200 K
KP 12m
The Map 1000″ x 800″ region 35″ spacing (half beam-size) 775 positions total 500 kHz resolution filterbanks 3 rms noise level < 20 mK
June 25, 200964th International Symposium on Molecular Spectroscopy
Further Observations• ARO SMT on Mt.
Graham• HCO+ (J = 3-2) 267.5576 GHz• ALMA-type Band 6
receiver
SMT
Examine select positions in the Helix and compare to J = 1-0 transition
June 25, 200964th International Symposium on Molecular Spectroscopy
(125, 185)
(390, -30)
(130, -180)
(-15, 270)
(-240, -100)
(-120, 240)
(-372, 0)
(-300, -200)
HCO+ J = 1-0
June 25, 200964th International Symposium on Molecular Spectroscopy
Beam Size (70″)
Helix Nebula (NGC 7293)
HCO+ J = 1 → 0
~16% complete 125 positions finished 3 rms noise level < 20 mK
CO J = 1 → 0Young et al. 1999
Beam Size (70″)
June 25, 200964th International Symposium on Molecular Spectroscopy
0.000
0.008
0.016
T R* / T
A* (K)
0.00
0.04
0.08
VLSR(km/s)-80 -24 32
0.0
0.3
0.6
(130, -180)
CO J= 1-0
HCO+
J= 1-0
HCO+
J= 3-2
-0.008
0.000
0.008
0.016
T R* / T
A*(K)
0.00
0.04
0.08
VLSR (km/s)-80 -24 32
0.0
0.2
0.4
(390, -30) HCO+
J= 3-2
HCO+
J= 1-0
CO J= 1-0
T R* / T
A*(K)
0.00
0.02
0.04
0.00
0.02
VLSR(km/s)-80 -24 32
0.0
0.1
0.2
(125, 185) HCO+
J= 3-2
HCO+
J= 1-0
CO J= 1-0
June 25, 200964th International Symposium on Molecular Spectroscopy
Summary• Chemistry in evolved planetary nebulae is more
active and complex than originally thought• Presence of HCO+ (J = 3-2) indicates that very dense
gas clumps exist in the Helix• HCO+ (J = 1-0) is widespread across the Helix and
can be used to identify more chemically interesting areas
June 25, 200964th International Symposium on Molecular Spectroscopy
Acknowledgements• Dr. Lucy Ziurys• Dr. DeWayne Halfen• Ziurys Group: Robin Pulliam, Emmy Tenenbaum,
Ming Sun, Gilles Adande, Jessica Dodd, Jie Min, Matthew Bucchino, Brent Harris
• ARO operators, engineers, and staff
• Funding: NASA and NSF