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Project Progress

The Organic Volatile Composition of Comets: C/2000 WM1 and 2P/Encke
and
A New Fluorescence Model for C₂H₆ ν₅ Applied to Eight Comets

*Yana L. Radeva, Catholic University of America and Goddard Center for Astrobiology, NASA GSFC*

Yana L. Radeva is a Research Associate at The Catholic University of America, and is conducting her postdoctoral research at NASA’s Goddard Space Flight Center. During the time period September 1, 2009 – August 30, 2010, she completed her dissertation on “Infrared Spectroscopy of Parent Volatiles in Comets: Chemical Diversity and a New Fluorescence Model for the Ethane ν₅ band”. Radeva received her Ph.D. in Astronomy, with advisors Dr. Michael Mumma (NASA GSFC) and Dr. Michael A’Hearn (University of Maryland), from the University of Maryland, College Park, in May 2010.

Yana L. Radeva published a paper on the organic composition of comet C/2000 WM₁ (LINEAR) in Icarus, the International Journal of Solar System Studies (Icarus, 2010, Volume 206, Issue 2, p. 764-777). The Oort Cloud comet WM₁ was observed on Nov. 23-25 2001, with NIRSPEC on the Keck II telescope; and Radeva presented production rates, rotational temperatures, and abundances relative to water, for the detected parent volatiles. WM₁ was found to be normal in C₂H₆, moderately depleted in HCN, CH₄ and CH₃OH, and severely depleted in C₂H₂ and CO. The abundances of organic species suggest homogeneity of the cometary nucleus, although there is insufficient temporal sampling.

Radeva completed the application of the new fluorescence model for the ν₅ band of C₂H₆ near 3.4 µm (developed in 2009), to eight comets: 17P/Holmes, C/2000 WM₁ (LINEAR), C/2004 Q2 Machholz (see Figure 1), C/2001 A2 (LINEAR), C/2007 N3 (Lulin), C/2007 W1 (Boattini), 8P/Tuttle and 2P/Encke. The ν5 band model is very valuable because it permits the extraction of rotational temperatures for C₂H₆, unlike the C₂H₆ ν₇ band (3.35 µm), which can only provide an accurate production rate. Furthermore, the C₂H₆ ν₅ band is measured simultaneously (thus, minimizing systematic errors) with H₂CO, CH₄, HCN, C₂H₂, NH₃, and H₂O, while the C₂H₆ ν₇ band is measured in the same setting only with CH₃OH and H₂O. Radeva demonstrated that the C₂H₆ ν₅ model can be used to derive reliable production rates and rotational temperatures for this molecule, and found agreement among the rotational temperatures derived for C₂H₆, HCN and H₂O. She presented the application of the new model in her Ph.D. dissertation, and at the Astrobiology Science Conference in April 2010 (AbSciCon 2010, League City, Texas). Radeva is also completing a paper on the C₂H₆ ν₅ model.

As part of her Ph.D. research, Yana L. Radeva analyzed the organic composition of the ecliptic comet 2P/Encke, observed with NIRSPEC on Keck II on 4-6 Nov. 2003. Radeva extracted production rates and mixing ratios for H₂O, CH₄, C₂H₂, C₂H₆, CH₃OH, H₂CO, and HCN, measured on Nov. 4; and CO, measured on Nov. 5. The rotational temperatures derived for H2O and HCN are very low (20-40 K), and Encke is moderately to significantly depleted in all detected species, except for CH₃OH, when compared to “organics-normal” comets. Radeva is completing her analysis of the organic composition of comet Encke, and a paper is in progress.

Yana L. Radeva commenced her GCA postdoctoral research on June 1, 2010, and is analyzing high-resolution infrared spectra of the Martian atmosphere, in a search for biomarker gases. She will be extracting information on trace gases such as CH₄ and CO₂, and studying Martian atmospheric conditions (such as surface temperature and pressure). Radeva will be studying the seasonal evolution of the retrieved gas abundances, and will use the results to create spatial maps of the Martian atmosphere.

Publications:
Radeva, Y. L., Mumma, M. J., Bonev, B. P., DiSanti, M. A., Villanueva, G. L., Magee-Sauer, K., Gibb, E. L., and Weaver, H. A, 2010. The organic composition of Comet C/2000 WM1 (LINEAR) revealed through infrared spectroscopy, Icarus, 206, 2, p. 764-777