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Observations of HCN in comet P/Halley
F P Schloerb1, W M Kinzel, D A Swade
1Five College Radio Astronomy Observatory, University of Massachusetts, Amherst 01003, USA.
Astronomy and Astrophysics
|November 1, 1987
Summary
Observations of hydrogen cyanide (HCN) in comet P/Halley reveal it is a minor gas constituent and a major parent of CN. Its production rate correlates with comet brightness, showing variability and outflow velocity changes.
Area of Science:
- Cometary Science
- Astrochemistry
- Planetary Science
Background:
- Comet P/Halley is a periodic comet known for its complex composition.
- Understanding cometary outgassing is crucial for studying solar system formation.
- Hydrogen cyanide (HCN) is a key molecule in cometary atmospheres.
Purpose of the Study:
- To extensively monitor the HCN J = 1-0 rotational transition in comet P/Halley.
- To determine the production rate and abundance of HCN relative to other cometary species.
- To investigate the relationship between HCN and other cometary emissions, such as CN.
Main Methods:
- Utilized 3.4 mm wavelength observations of the HCN J = 1-0 rotational transition.
- Conducted 56 individual observing sessions between November 1985 and May 1986.
- Analyzed spectral data, including line width and hyperfine ratios, binned by heliocentric distance.
Main Results:
- HCN production rate is strongly correlated with comet P/Halley's visual magnitude.
- HCN is a minor constituent (0.1% of H2O abundance) but a major parent molecule for CN.
- Outflow velocity increases with decreasing heliocentric distance; blue shifts suggest anisotropic outgassing.
Conclusions:
- HCN is a significant, though minor, volatile in comet P/Halley, influencing CN production.
- Observed variability in HCN emission aligns with known cometary behavior.
- Discrepancies in non-LTE hyperfine ratios suggest limitations in current excitation models.