A Study of HCO + and CS in Planetary Nebulae Jessica L. Edwards Lucy M. Ziurys Nick J. Woolf The University of Arizona Departments of Chemistry and Astronomy The 66th Ohio State University International Symposium on Molecular Spectroscopy

Dense Clouds – Cold, dense regions of space. 75% of molecules found in ISM Star Formation Regions – Instabilities cause molecular cloud to collapse, stars/planetary systems form Evolved Stars – stars age and die. Experience mass loss, molecule-rich circumstellar envelope (over 70 molecules detected in CSE’s) Planetary Nebulae (PNe) – Hot, UV emitting central star surrounded by neutral and ionized gaseous material. Supplies 80% of material to the ISM. Diffuse Clouds – material forms diffuse clouds which then collapse to dense clouds. The Life Cycle of material in the Interstellar Medium

The Molecular Life Cycle e Planetary Nebulae Diffuse Clouds Dense Clouds Star Formation Cloud Dispersion Protoplanetary Disks Other Solar Systems Evolved Stars

Planetary Nebulae Majority of stars (from ~0.5-8 M  ) will become PNe Hot (~100,000 to 400,000 K), UV emitting central star surrounded by gaseous material from molecule rich Circumstellar Envelope Molecular material is flowing outward but being ionized by central star Initially thought that all molecular matter would be destroyed in PN, photodissociated by central star Ionized material accounts for a small percentage of the old stellar mass. Where is the rest? 80% of material going into ISM! Can molecules survive in this harsh environment?

The Helix Nebula Oldest known PN, ~11,000 years old Molecules have been subject to UV radiation Previously seen CO, HCO +, CN, HCN, HNC (Bachiller et al. 1997) Recently detected H 2 CO, c-C 3 H 2, and C 2 H (Tenenbaum et al. 2009) HCO + and H 2 CO all over the Helix

Background/previous work Chemical evolution study by Bachiller et al. (1997) – Studied a number of proto-planetary and planetary nebulae of various ages. – It was proposed that certain molecules “disappeared” or were not detected in PNe due to chemical evolution from photo-dissociation Survey of NGC 7027 by Zhang, Kwok, and Trung (2008) – Identified 67 lines from 8 molecules including CO, CN, C 2 H, C 3 H 2, HCN, HCO +, HCS +, HC 3 N, and N 2 H +

LineFrequency (GHz)Receiver CO(6-5) mm SIS (WF03) CO(2-1) mm ALMA Type CS(5-4) mm ALMA Type HCO + (3-2) mm ALMA Type LineFrequency (GHz)Receiver CS(3-2) mm SIS CS(2-1) mm ALMA Type HCO + (1-0) mm ALMA Type SMT Observations 12 m Observations Source Info. Source nameRADec K4-4704:20:45.256:18:12.1 M2-4819:50:28.525:54:29.5 NGC :05: :50:34.9 NGC :53:35.133:01:45.0 NGC 6853 (offset)19:57:21.922:33:57.2 Photos courtesy of the Arizona Radio Observatory and Dave Harvey

CO(6-5) HCO + (3-2) HCO + (1-0) CS(5-4) CS(3-2) CS(2-1) K4-47 Age is uncertain. Young, compact source. Between 900 and 2,000 years old. ~0.2’

HCO + (3-2) HCO + (1-0) CS(5-4) CS(3-2) CS(2-1) M2-48 Estimated to be between 3,000 and 5,000 years old. ~32”

HCO + (3-2) HCO + (1-0) CS(5-4) CS(3-2) CS(2-1) CO(6-5) NGC 6537 (The Red Spider) Young planetary nebula at 1,600 years old. Central star is one of the hottest white dwarfs known with T* ~400,000 K. ~2’ ~0.5’ ~1.2’ ~0.2’

HCO + (1-0) CS(5-4) CS(3-2) CS(2-1) CO(2-1) HCO + (3-2) NGC 6720 (The Ring) Old source, age ~7,000 years ~1.5’ ~0.5’ ~1.2’

NGC 6853 (The Dumbbell) VLT Image Oldest source CS has been detected in at ~10,000 years old. ~5.5’ ~0.5’ ~1.2’ CS(5-4) CO(2-1) HCO + (1-0) CS(3-2) CS(2-1) HCO + (3-2)

Age does not seem to matter Sources have different molecular content, possibly originating from different chemistries in the progenitor AGB star SourceAge (years)MoleculeColumn Density (p cm -2 ) K ,000 HCO x CS 4.2 x NGC HCO x CS 2.3 x M2-483,000-5,000 HCO x CS 5.4 x NGC 67207,000 HCO + ~1 x CS ~2 x NGC ,000 HCO + ~2 x CS ~3 x 10 12

What about Diffuse Clouds? Lucas and Liszt, Liszt, Lucas, and Pety, 2006 Sixteen molecules have been seen in diffuse clouds Thirteen can be seen in these sources Seen in absorption against a background source DIB carriers?

Diffuse Clouds vs. Planetary Nebulae Molecules seen in Diffuse Clouds Molecules seen in Planetary Nebulae CO, CH, C 2 H, C 3 H 2, HCO +, CN, HCN, HNC, NH 3, OH, H 2 CO, CS, HCS +, H 2 S, SO, SiO CO, C 2 H, C 3 H 2, HCO +, CN, HCN, HNC, N 2 H +, OH, H 2 CO, HCS +, CS (this work) CO, HCO +, CN, HCN have been seen in multiple young and old sources C 2 H and C 3 H 2 have been seen in NGC 7027 and the Helix H 2 CO and HNC have been seen in old sources HCS +, N 2 H +, and OH have been seen in NGC 7027

Conclusions Planetary Nebula age does not appear to matter Molecules can definitely survive the PNe stage If molecules can survive the intense radiation in a PN for 12,000 years, they can survive in the ISM and be recycled into Diffuse Clouds! Greater chemical complexity in the ISM can be achieved, not starting with atoms Interesting chemical variation and velocity structure in PNe that have to be investigated

Future Directions Different chemical species (H 2 S, SO, SiO) Studies of VY Canis Majoris, an oxygen rich star, reveal a large content of sulfur- bearing molecules Carbon rich PNe vs. Oxygen rich PNe? (This topic has not even been considered)

Acknowledgements Dr. Ziurys, Dr. Woolf Dr. Emily Tenenbaum, Lindsay Zack The rest of the Ziurys Group Arizona Radio Observatory Engineers, Operators NASA and NSF for funding