HCO in Oxygenrich Stars Investigating IonMolecule Chemistry In

HCO+ in Oxygen-rich Stars: Investigating Ion-Molecule Chemistry In Circumstellar Environments Robin L. Pulliam Lucy M. Ziurys Depts. of Chemistry and Astronomy, Steward Observatory and Arizona Radio Observatory

Background – HCO+ very abundant in molecular clouds – It’s detection in circumstellar envelopes has been elusive – Models of oxygen-rich circumstellar envelopes predicting the presence of HCO+ are sparse – Only recently detected around one oxygen-rich star, VY CMa Continuing the search for HCO+ around o-rich evolved stars

Evolved Oxygen-rich Stars Circumstellar Envelopes Evolved stars Oxygen-rich chemistry C/O ratio is less than 1 PLANETARY NEBULA Stellar envelope completely detached 3. 40 — 6. 00 — MASS > 10 MΘ Sun-like • Most stars investigated are in the early AGB phase • O-rich evolved stars haven’t yet undergone third dredge- up To White 3. 25 5. 50—— Dwarf 40 MΘ Log (L) Hertzsprung-Russell diagrams 5. 00—— 3. 10 AGB He & H Shell Burning Envelope H Shell Burning 25 MΘ 4. 50 — 2. 95 — 4. 00 — 2. 80 — 4. 30 PROTO-PLANETARY NEBULA (PPN) Nucleosynthesis stops CRL 2688 He Core Burning H Shell Narrows Triple -Process RED GIANT BRANCH MAIN SEQUENCE 15 MΘ Burning Hydrogen Core First Dredge-up: Sun Surface Abundances Change 4. 5 4. 00 3. 50 4. 15 4. 00 3. 85 3. 60 Log (Te) (T ) e

Modeling of Oxygen-Rich Stars • Modeling of o-rich circumstellar envelopes of AGB stars by Mamon et al. in 1987 • HCO+ abundance decreases as mass loss rate increases CO + H 3+ HCO+ + H 2 HCO+ CO + N 2 H+ HCO+ C+ + H 2 O HCO+ + OH H 3 O+ HCO+ + H 2 O H 3 O+ Mamon et al. , Ap. J, 323, 1987 CO + H 3+ HCO+ + H 2 HCO+ CO + N 2 H+ HCO+ C+ + H 2 O HCO+ + OH H 3 O+ HCO+ + H 2 O H 3 O+

Recent Detection of HCO+ in VY CMa • Recent observations show HCO+ in this star (Ziurys et al. , Nature, 1094, 2007) – Oxygen-rich supergiant – ~25 solar masses – 2 x 10 -4 Mʘ yr-1 – Calculated abundance of HCO+ : 2 x 10 -8 Sun Kwok, Nature, 447, 2007 Figure Courtesy of Stefanie Milam

HCO+ Observations using ARO telescopes • The 12 -m telescope on Kitt Peak - Frequency range: 65 -116 and 125 -180 GHz • The Sub-millimeter telescope on Mt. Graham - Frequency range: 210 -279, 320 -375, and 600 -720 GHz 12 m SMT

Oxygen-Rich Stars Source Star Type Mass Loss Rate (Mʘ) (Mʘ yr-1) NML Cyg 1 Supergiant Distance (pc) VLSR (km s-1) Coordinates (B 1950. 0) 50 (1 -2)x 10 -5 1800 -5. 0 03: 50: 43. 6 11: 15: 32. 2 IK Tau 2 AGB 1 (2 -5)x 10 -6 250 34. 5 20: 44: 33. 8 39: 55: 57. 0 TX Cam 3 AGB 1 3 x 10 -6 450 9. 2 04: 56: 40. 6 56: 06: 28. 0 W Hya 4 AGB 1 3. 5 x 10 -7 115 41. 0 13: 46: 12. 2 -25: 40: 12. 0 Transition J+1 J 1 0 2 1 3 2 4 3 1 Boboltz Frequency (MHz) 89188. 523 178375. 010 267557. 526 356734. 134 et al. , Ap. J, 545, 2000 et al. , Ap. J, 625, 2005 3 Olofsson et al. , A&A, 245, 1991 4 Justtanont, et al. , A&A, 417, 2005 2 Boboltz Wavelength (mm) 3. 4 1. 7 1. 1 0. 8 Beam Size (arcsecs) 70 35 28 21 Telescope ARO 12 m ARO SMT

Observational Results Current Observational Results: Tau • • IK IKTau • Detected the J=1 -0 and J=3 -2 • • Detected J=3 -2 blended the with SOJ=1 -0 and • W Hya J=3 -2 • W • Hya Detected. J=1 -0 and J=3 -2 with. J=3 SO 2 • • • J=3 -2 Narrow lineblended profiles Detected J=1 -0 and 42 hrs 36 hrs 69 2 • J=3 -2 -2 is not blended with SO 2 • TX TX Cam • Cam Narrow line profiles • Proving more difficult • • J=3 -2 is more not blended Proving difficult The J=1 -0 emerging from the noise SO 2 emerging from • • with The J=1 -0 The J=3 -2 needs more integration time noise with SO 2 • the Contaminated • The J=3 -2 needs more integration time • NML Cyg • Contaminated with SO 2 • All four transitions observed • Both J=3 -2 and J=4 -3 blended with SO 2 • 6430 hrs 100 hrs

Observational Results 66 hrs 41 hrs 43 hrs 62 hrs

Column Densities and Current Analysis • Preliminary analysis: constructed rotational diagram and determined column densities • Tentative agreement; need to calculate fractional abundances Source Column Density (cm-2) Tex (K) IK Tau NML Cyg TX Cam W Hya 1. 4 x 1011 1. 8 x 1011 1. 3 x 1011 5. 7 x 1010 8 8 8* 10 Source Mass (Mʘ) Mass Loss Rate (Mʘ yr-1) NML Cyg 1 IK Tau 2 TX Cam 3 50 1 1 (1 -2)x 10 -5 (2 -5)x 10 -6 3 x 10 -6 W Hya 4 VY CMa 1 25 3. 5 x 10 -7 2 x 10 -4 1 Boboltz Source Mass (Mʘ) Mass Loss Rate (Mʘ yr-1) NML Cyg 1 IK Tau 2 TX Cam 3 50 1 1 (1 -2)x 10 -5 (2 -5)x 10 -6 3 x 10 -6 W Hya 4 1 3. 5 x 10 -8 et al. , Ap. J, 545, 2000; 2 Boboltz et al. , Ap. J, 625, 2005; 3 Olofsson et al. , A&A, 245, 1991; 4 Justtanont, et al. , A&A, 417, 2005 Mamon et al. , 1987

Conclusions and Future Work • Four new detections of HCO+ in evolved oxygenrich stars • HCO+ common constituent in these stars • Finish observations this up coming Fall: ØJ=2 1 in IK Tau, TX Cam, and W Hya ØJ=3 2 in TX Cam ØJ=4 3 in IK Tau, TX Cam, and W Hya • Tentative agreement with model by Mamon et al. • Model line profiles, determine abundances of HCO+ to help further understand ion-molecule chemistry in circumstellar envelopes

Acknowledgements • • • Prof. Lucy Ziurys Dr. De. Wayne Halfen Emmy Tenenbaum Ming Sun Lindsay Zack Jessica Dodd Gilles Adande ARO telescope operators and staff NSF and NASA for funding