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Definitive Detection of Formaldehyde Emission in Comets at Infrared Wavelengths

This study presents the first definitive line-by-line detection of formaldehyde (H2CO) in comets, specifically focusing on the comet C/2002 T7 (LINEAR). The presence of formaldehyde in comets is significant for astrobiology, as it may provide insights into the origin of life. This research utilizes advanced modeling techniques to compare the abundances of formaldehyde and related molecules with theoretical predictions and laboratory simulations. The results contribute to understanding the processes that form organic molecules in cometary environments.

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Definitive Detection of Formaldehyde Emission in Comets at Infrared Wavelengths

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  1. Formaldehyde Emission in C/2002 T7 (LINEAR): First Definitive Line-by-Line Detection in Comets at Infrared Wavelengths

  2. Acknowledgements • NASA Astrobiology Program (RTOP 344-53-51) • NASA Planetary Atmospheres Program (RTOP 344-33-55) • NASA Planetary Astronomy Program (RTOP 344-32-98)

  3. SIGNIFICANCE OF H2CO AND OXIDIZED CARBON IN COMETS • The presence of formaldehyde and related molecules in comets may provide key information pertaining to the origin of life. • Relevance to Astrobiology • H2CO is fundamental in studies of oxidized carbon in comets. • Its likely means of production is repeated hydrogen addition to CO ice in grain mantles prior to their incorporation into the nucleus: CO ice + H -----> HCO -----> H2CO -----> CH3OH Such reactions have been confirmed in laboratory simulations (Hudson and Moore 1999 Icarus140:361; Watanabe et al. 2004 ApJ616:638). Provides a quantitative comparison for our retrieved abundances of CO, H2CO and CH3OH in comets.Our measured mixing ratios CO:H2CO:CH3OH in cometary nuclei can test the efficiency for hydrogenation of CO on ice-mantled grains. 19mar06md

  4. Hudson & Moore 1999 Icarus140:451

  5. Modeling of Cometary Formaldehyde • Line-by-line fluorescence model (Reuter et al. 1989 ApJ341:1045) • Two fundamental bands: n1 (symmetric C-H stretch) & n5 (asymmetric C-H stretch). Recent applicability to high-res spectra. • Compare predicted line intensities with those observed in our comet spectra: • Correlation analysis to constrain rotational temperature. • Excitation analysis to rigorously obtain Trot, sTrot; hence Q. We have detected H2CO (n1 Q-branch) in 7 out of 12 comets observed since 1999. The best candidate for comparison with and testing of modeled line intensities is C/2002 T7 (LINEAR). 19mar2006md

  6. Formaldehyde fluorescencemodel (n1-, n5-bands). Reuter et al. Ap. J.341:1045 (1989) 29june04md 19mar2006md

  7. CSHELL (C/T7) 20mar06md

  8. C/T7 May 5 (D-F), May 7 (G), 15-row (1 x 3 arc-sec) sums 07nov05md

  9. 05nov04md

  10. --> --> 05nov04md

  11. 05nov04md

  12. 05nov04md

  13. 05nov04md

  14. 05nov04md

  15. 05nov04md

  16. 05nov04md

  17. 05nov04md

  18. Treat each setting separately… • avoids the question of inter-calibrating settings • provides additional insights 07nov2005md

  19. Correlation Analysis: Most Probable Trot DiSanti et al. 2006 ApJ (submitted) 21mar2006md

  20. 3-s 18mar06md

  21. C/2002 T7 (LINEAR) excitation analysis, UT 2004 May 05 DiSanti et al. 2006 ApJ (submitted) 20mar2006md

  22. Correlation Analysis: Most Probable Trot DiSanti et al. 2006 ApJ (submitted) 21mar2006md

  23. A-C: C/2002 T7 (LINEAR), UT 2004 May 05, CSHELL Hudson & Moore 1999 Icarus 140:451 Hudson & Moore 1999 Icarus 140:451 Hudson & Moore 1999 Icarus 140:451 20mar2006md

  24. Volatile Carbon Mixing Ratios (H2O = 100) and CO Conversion Efficiencies (still evolving!!) 20mar2006md

  25. Conclusions • H2CO fluorescence model is validated in C/2002 T7. • H-atom addition to CO to form H2CO and CH3OH on interstellar grain ice mantles at T ~ 10 - 15 K appears plausible, based on comparison with laboratory irradiation experiments. 16sep2005md

  26. Future Directions • Finalize native source contributions (esp. CO, H2CO). • Investigate potential additional emitting species (including isotopes) in 2760 - 2800 cm-1 region. • OPR (Tspin). 20mar2006md

  27. 104 yrs 105 yrs 106 yrs 20mar2006md

  28. 104 yrs 105 yrs 106 yrs 20mar2006md

  29. NIRSPEC (C/Lee) ------------------------ CSHELL (C/T7) 20mar06md

  30. C/1999 H1 (Lee), UT 1999 Aug 21.6, NIRSPEC Q-br | CSHELL CSHELL 29june04md 16sep2005md

  31. C/1999 H1 Lee, UT 1999 August 21.6 NIRPSEC 19mar2006md

  32. Comparison of Spatial Profiles(isolation of native source contribution) 16sep2005md

  33. | | 05nov04md

  34. “Excess” Emission in C/T7 -- CH3OH n3-band 05nov04md

  35. “Excess” Emission in C/T7 -- HDCO, etc (???) NIRSPEC ------------------------ 05nov04md

  36. 100 K model (fully-resolved, Doppler-shifted by -66 km s-1) H2CO Ortho, Para states 16sep2005md

  37. Hints for the thermal equilibrium process Nuclear spin temperature [K] Crovisier (1998)

  38. H2CO@40K -KL2-order21 - July 4, 2005

  39. CH4@40K -KL2-order23 - July 4, 2005

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