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HCO + in the Helix Nebula

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.

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HCO + in the Helix Nebula

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  1. 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

  2. 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

  3. 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? Tenenbaum et al., in preparation

  4. 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 and vibrationally excited H2 • Interesting structure • Cometary globules

  5. CO (J = 2-1) Map of the Helix Young et al. 1999 Multiple Velocity Components

  6. 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

  7. 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

  8. 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 • 3s rms noise level < 20 mK

  9. 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

  10. HCO+ J = 1-0 (125, 185) (-15, 270) (-120, 240) (390, -30) (-372, 0) (130, -180) (-240, -100) (-300, -200)

  11. Helix Nebula (NGC 7293) HCO+ J = 1 → 0 • ~16% complete • 125 positions finished • 3s rms noise level < 20 mK Beam Size (70″) Beam Size (70″) CO J = 1 → 0 Young et al. 1999

  12. 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

  13. 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

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