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– HCO + very abundant in molecular clouds – It’s detection in circumstellar envelopes has been elusive – Models of oxygen-rich circumstellar envelopes.

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Presentation on theme: "– HCO + very abundant in molecular clouds – It’s detection in circumstellar envelopes has been elusive – Models of oxygen-rich circumstellar envelopes."— Presentation transcript:

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2 – 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

3 Most stars investigated are in the early AGB phase O-rich evolved stars haven’t yet undergone third dredge- up 2.80 — 3.40 — 2.95 — 3.10 — 3.25 — 3.60 3.854.004.154.30 PLANETARY NEBULA Stellar envelope completely detached To White Dwarf PROTO-PLANETARY NEBULA (PPN) Nucleosynthesis stops CRL2688 AGB He & H Shell Burning Envelope Triple  -Process RED GIANT BRANCH H Shell Narrows H Shell Burning First Dredge-up: Surface Abundances Change MAIN SEQUENCE Hydrogen Core Burning Sun Log (L) Log (T e ) He Core Burning Evolved stars Oxygen-rich chemistry C/O ratio is less than 1 4.00 — 6.00 — 4.50 — 5.00 — 5.50 — 3.50 4.004.5 Log (L) Log (T e ) 25 M Θ 15 M Θ 40 M Θ

4 Modeling of o-rich circumstellar envelopes of AGB stars by Mamon et al. in 1987 HCO + abundance decreases as mass loss rate increases Mamon et al., ApJ, 323, 1987

5 Recent observations show HCO + in this star (Ziurys et al., Nature, 1094, 2007) – Oxygen-rich supergiant – ~25 solar masses – 2x10 -4 M ʘ yr -1 – Calculated abundance of HCO + : 2x10 -8 Figure Courtesy of Stefanie MilamSun Kwok, Nature, 447, 2007

6 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

7 1 Boboltz et al., ApJ, 545, 2000 2 Boboltz et al., ApJ, 625, 2005 3 Olofsson et al., A&A, 245, 1991 4 Justtanont, et al., A&A, 417, 2005 SourceStar TypeMass (M ʘ ) Mass Loss Rate (M ʘ yr -1 ) Distance (pc) V LSR (km s -1 ) Coordinates (B1950.0) NML Cyg 1 Supergiant50(1-2)x10 -5 1800-5.003:50:43.6 11:15:32.2 IK Tau 2 AGB1(2-5)x10 -6 25034.520:44:33.8 39:55:57.0 TX Cam 3 AGB13x10 -6 4509.204:56:40.6 56:06:28.0 W Hya 4 AGB13.5x10 -7 11541.013:46:12.2 -25:40:12.0 Transition J+1  J Frequency (MHz) Wavelength (mm) Beam Size (arcsecs) Telescope 1  0 89188.5233.470ARO 12m 2  1 178375.0101.735ARO 12m 3  2 267557.5261.128ARO SMT 4  3 356734.1340.821ARO SMT

8 Current Observational Results: IK Tau Detected the J=1-0 and J=3-2 J=3-2 blended with SO 2 TX Cam Proving more difficult The J=1-0 emerging from the noise The J=3-2 needs more integration time Contaminated with SO 2 W Hya Detected J=1-0 and J=3-2 Narrow line profiles J=3-2 is not blended with SO 2 NML Cyg All four transitions observed Both J=3-2 and J=4-3 blended with SO 2 IK Tau Detected the J=1-0 and J=3-2 J=3-2 blended with SO 2 W Hya DetectedJ=1-0 and J=3-2 Narrow line profiles J=3-2 is not blended with SO 2 TX Cam Proving more difficult The J=1-0 emerging from the noise The J=3-2 needs more integration time Contaminated with SO 2 36 hrs 30 hrs 69 hrs 64 hrs 42 hrs 100 hrs

9 66 hrs 62 hrs 43 hrs 41 hrs

10 SourceMass (M ʘ ) Mass Loss Rate (M ʘ yr -1 ) NML Cyg 1 50(1-2)x10 -5 IK Tau 2 1(2-5)x10 -6 TX Cam 3 13x10 -6 W Hya 4 13.5x10 -7 VY CMa252x10 -4 SourceColumn Density (cm -2 ) T ex (K) IK Tau1.4 x10 11 8 NML Cyg1.8 x10 11 8 TX Cam1.3 x10 11 8*8* W Hya5.7 x10 10 10 Preliminary analysis: constructed rotational diagram and determined column densities Tentative agreement; need to calculate fractional abundances SourceMass (M ʘ ) Mass Loss Rate (M ʘ yr -1 ) NML Cyg 1 50(1-2)x10 -5 IK Tau 2 1(2-5)x10 -6 TX Cam 3 13x10 -6 W Hya 4 13.5x10 -8 Mamon et al., 1987 1 Boboltz et al., ApJ, 545, 2000; 2 Boboltz et al., ApJ, 625, 2005; 3 Olofsson et al., A&A, 245, 1991; 4 Justtanont, et al., A&A, 417, 2005

11 Four new detections of HCO + in evolved oxygen- rich stars HCO + common constituent in these stars Finish observations this up coming Fall:  J=2  1 in IK Tau, TX Cam, and W Hya  J=3  2 in TX Cam  J=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

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

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15 Outline Background of HCO+ Past modeling of oxygen-rich stars Past detection of HCO+ in the supergiant VY CMa Stars investigated in this study and current observations Conclusions

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