june 21, 2013 68 th international symposium on molecular spectroscopy nicholas r. zeigler lindsay n....

June 21, 201368th International Symposium on Molecular Spectroscopy

Nicholas R. ZeiglerLindsay N. ZackNeville J. WoolfLucy M. Ziurys Department of Chemistry Department of Astronomy Steward Observatory Arizona Radio Observatory University of Arizona

HCO+ in the Helix Nebula

June 21, 201368th 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 21, 201368th International Symposium on Molecular Spectroscopy

Morphologies

June 21, 201368th International Symposium on Molecular Spectroscopy

The Helix Nebula

Age: ~12,000 years

Distance: ~200 pc

Angular Size: ~1000”

• Very old• Lots of dust and gas

• Atomic gas : Ha, N II, O I, C I

• Molecular gas: CO , H2,

• Polyatomic molecules: C3H2, H2CO

(Tenenbaum et al 2009)

• Interesting structure• Cometary globules

June 21, 201368th International Symposium on Molecular Spectroscopy

The Helix Nebula

Age: ~12,000 years

Distance: ~200 pc

Angular Size: ~1000”

• Very old• Lots of dust and gas

• Atomic gas : Ha, N II, O I, C I

• Molecular gas: CO , H2,

• Polyatomic molecules: C3H2, H2CO

(Tenenbaum et al 2009)

• Interesting structure• Cometary globules

Taylor 1977

June 21, 201368th International Symposium on Molecular Spectroscopy

The Helix Nebula

Age: ~12,000 years

Distance: ~200 pc

Angular Size: ~1000”

• Very old• Lots of dust and gas

• Atomic gas : Ha, N II, O I, C I

• Molecular gas: CO , H2,

• Polyatomic molecules: C3H2, H2CO

(Tenenbaum et al 2009)

• Interesting structure• Cometary globules

O’Dell et al. 2004

June 21, 201368th International Symposium on Molecular Spectroscopy

Globules

June 21, 201368th International Symposium on Molecular Spectroscopy

CO (J = 2-1) Map of the Helix

Young et al. 1999

Multiple Velocity Components

June 21, 201368th International Symposium on Molecular Spectroscopy

Why HCO+ ?• m = 3.89 D

• High critical density (ncr ~ 105 cm-3) indicates that HCO+ emission is present in dense gas around the Helix– CO: m = 0.11 D; ncr ~ 103 cm-3

• Dense gas is shielding and can preserve molecules

June 21, 201368th 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 (84–116 GHz)

– Tsys < 200 K

– rms noise < 20 mK• Map across entire Helix

(~1000” x ~800”)

KP 12m

June 21, 201368th International Symposium on Molecular Spectroscopy

• 35″ spacing

• 129 positions

Beam Size (70″)

• 70″ spacing• 89 positions

Integration time ~2-3 hours

June 21, 201368th International Symposium on Molecular Spectroscopy

HCO+ Integrated Intensity

• Column densities:

– Range: Ntot ~ 1.4 × 1011 – 2.4 × 1012 cm-2

– Average: Ntot ~ 4 × 1011 cm-2

– Average f(HCO+/H2) ~ 5.3 × 10-8 cm-2

June 21, 201368th International Symposium on Molecular Spectroscopy

Comparing Atomic and Molecular emission

H2 Optical

HCO+ CO

June 21, 201368th International Symposium on Molecular Spectroscopy

Velocity Partitions

CO (Young et al 1999) HCO+ (J=1-0)

June 21, 201368th International Symposium on Molecular Spectroscopy

Velocity vs. Position Angle

Young et al 1999

CO

June 21, 201368th International Symposium on Molecular Spectroscopy

Velocity vs. Position AngleHCO+

June 21, 201368th International Symposium on Molecular Spectroscopy

Velocity vs. Position AngleHCO+

June 21, 201368th International Symposium on Molecular Spectroscopy

Red/Blue shift separated plots

Red shift Blue shift

June 21, 201368th International Symposium on Molecular Spectroscopy

H2 Overlays

-35 km/s -11 km/s

O’Dell ModelSpeck, A. 2002

June 21, 201368th International Symposium on Molecular Spectroscopy

3D Structure

June 21, 201368th International Symposium on Molecular Spectroscopy

Summary• The HCO+ emission is coincident with the CO

emission, indicating that dense gas exists throughout the Helix

• Molecular distribution corresponds with atomic emission, indicating that molecular material is ubiquitous.

• The model for the structure of the Helix has been improved.

June 21, 201368th International Symposium on Molecular Spectroscopy

Acknowledgements

FundingNASANSF

Ziurys GroupMatt Bucchino, Debbie Schmidt, DeWayne Halfen, Lucy Ziurys, Julie Anderson, Jessica Edwards, Jie Min, Gilles

Adande, and Debbie Schmidt