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

“COMET TEAM”: M. J. Mumma, B. P. Bonev (U. Toledo/GSFC), M. A.DiSanti, K. Magee-Sauer (Rowan U.), N. Dello Russo (JHU-APL), G. L.Villanueva (NAS-NRC/GSFC), E. L. Gibb (Notre Dame U.), W. Anderson(CUA/GSFC)

Acknowledgements

• NASA Astrobiology Program (RTOP 344-53-51)

• NASA Planetary Atmospheres Program (RTOP 344-33-55)

• NASA Planetary Astronomy Program (RTOP 344-32-98)

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 Icarus 140:361; Watanabe et al. 2004 ApJ 616:638).

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

Hudson & Moore1999 Icarus 140:451

Line-by-line fluorescence model (Reuter et al. 1989 ApJ 341:1045)

Two fundamental bands: 1 (symmetric C-H stretch) & 5 (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, Trot; hence Q.

We have detected H2CO (1 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

Modeling of Cometary Formaldehyde

29june04md

Form

aldeh

yde flu

orescence m

odel (

1-, 5-

ban

ds). Reu

ter et al. Ap. J. 341:1045 (1989)

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CSHELL (C/T7)

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

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-->-->

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Treat each setting separately… avoids the question of inter-calibrating settings provides additional insights

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Correlation Analysis: Most Probable Trot

DiSanti et al. 2006 ApJ (submitted)

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d

3-

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C/2002 T7 (LINEAR) excitation analysis, UT 2004 May 05

DiSanti et al. 2006 ApJ (submitted)

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Correlation Analysis: Most Probable Trot

DiSanti et al. 2006 ApJ (submitted)

Hudson & Moore1999 Icarus 140:451

A-C: C/2002 T7 (LINEAR), UT 2004 May 05, CSHELL

Hudson & Moore1999 Icarus 140:451

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Hudson & Moore1999 Icarus 140:451

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

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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.

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Future Directions

Finalize native source contributions (esp. CO, H2CO).

Investigate potential additional emitting species (including isotopes) in 2760 - 2800 cm-1 region.

OPR (Tspin).

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104 yrs

105 yrs

106 yrs

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106 yrs

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NIRSPEC (C/Lee)------------------------

CSHELL (C/T7)

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Q-br|

C/1999 H1 (Lee), UT 1999 Aug 21.6, NIRSPEC

CSHELL CSHELL

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C/1999 H1 Lee, UT 1999 August 21.6 NIRPSEC

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Comparison of Spatial Profiles(isolation of native source contribution)

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“Excess” Emission in C/T7 -- CH3OH 3-band

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NIRSPEC------------------------

“Excess” Emission in C/T7 -- HDCO, etc (???)

100 K model (fully-resolved, Doppler-shifted by -66 km s-1)

H2CO Ortho, Para states

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Hints for the thermal equilibrium Hints for the thermal equilibrium process process

Crovisier (1998)

Nuclear spin temperature [K]

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

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