Hidden molecules in planetary nebulae: New detections of HCN and HCO{sup +} from a multi-object survey

Journal Article · Mon Feb 01 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/817/2/175· OSTI ID:22887071

Schmidt, D. R.; Ziurys, L. M. ^[1]

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1. Department of Astronomy and Steward Observatory, University of Arizona, 933 N. Cherry Avenue Tucson, AZ 85721-0065 (United States)

Searches for HCN and HCO{sup +} have been conducted toward 17 planetary nebulae (PNs) in the age range 800 to 13,000 years using the facilities of the Arizona Radio Observatory (ARO). For both molecules, observations of the J=1→0 transition near 88–89 GHz were carried out with the ARO 12 m, including measurements with the new ALMA prototype antenna, while the J=3→2 lines near 265–267 GHz were sought with the ARO Sub-Millimeter Telescope (SMT). HCN and HCO{sup +} were newly detected in 13 of the 17 target sources in at least one transition. Nine PNs were common to both molecules: Hb5, K3-17, K3-58, M1-7, M4-14, M3-28, M3-55, NGC 2440, and K4-47, while HCO{sup +} was also identified in K3-83 and M2-9, and HCN in K3-45 and NGC 6772. From radiative transfer modeling, column densities for HCN and HCO{sup +} in these sources were determined to be N{sub tot}(HCN) ∼ 0.2–27 × 10{sup 13} cm{sup −2} and N{sub tot}(HCO{sup +}) ∼ 0.3–8.7 × 10{sup 13} cm{sup −2}. Gas densities, assumed to be in clumped regions, were established to be n(H{sub 2}) ∼ 0.1–5.2 × 10{sup 6} cm{sup −3}. Fractional abundances, relative to H{sub 2}, for both molecules were found to be f(HCN) ∼ 0.1–9.1 × 10{sup −7} and f(HCO{sup +}) ∼ 0.04–7.4 × 10{sup −7}. The abundances of both species were found to remain relatively constant with nebular age over a 10,000 year time span, in contrast to predictions of chemical models. The HCN/HCO{sup +} ratio varied from 17 to <0.2, and roughly correlates with the C/O ratio. Polyatomic molecules appear to be common constituents of PNs.

• OSTI ID: 22887071
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 817; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPUTERIZED SIMULATION
COSMIC GASES
DENSITY
DETECTION
ELEMENT ABUNDANCE
FORECASTING
GHZ RANGE 100-1000
HYDROGEN
MOLECULES
PLANETARY NEBULAE
RADIANT HEAT TRANSFER
TELESCOPES