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 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

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+ CS C2H C3H2 SiS Tenenbaum et al., in preparation

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

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

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

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

HCO+ Observations The Map 1000″ x 800″ region 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

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

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

Helix Nebula (NGC 7293) HCO+ J = 1 → 0 CO J = 1 → 0 Young et al. 1999 ~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

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

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