Search for mid-IR rotational and ν1→ν2 difference band emission in Jupiter’s northern aurora
✍ Scribed by Laurence M. Trafton; Steven Miller; John H. Lacy; Thomas K. Greathouse
- Book ID
- 103830541
- Publisher
- Elsevier Science
- Year
- 2009
- Tongue
- English
- Weight
- 944 KB
- Volume
- 203
- Category
- Article
- ISSN
- 0019-1035
No coin nor oath required. For personal study only.
✦ Synopsis
Using TEXES at the IRTF telescope, we obtained high-resolution, mid-infrared, longslit spectra of Jupiter's northern auroral ''hot spot" near System III longitude 180°to search for selected pure-rotational and m 1 ?m 2 difference band lines of H þ 3 . Because these lines have not been investigated in the laboratory, we used theoretically predicted frequencies and line intensities to guide this search. No pure rotational H þ 3 line emission was detected near the predicted frequencies. However, two metastable m 1 ?m 2 difference band lines appear to have been marginally detected at the 68% confidence level (1 À r). The non-detection of the pure rotational line sets a 1 À r upper limit to the vertical column abundance of H þ 3 in the northern jovian aurora of 8.4 Â 10 12 cm À2 , which is independent of any assumption concerning the departure of the vibrational H þ 3 energy level populations from thermal equilibrium. This is consistent with the column 6 Â 10 12 cm À2 inferred by Melin et al. [Melin, H., Miller, S., Stallard, T., Grodent, D., 2005. Icarus 178, 97-103] from their non-LTE H þ 3 emission model, in which the fundamental band rovib levels are underpopulated by a factor of 6-10 relative to LTE. We find that the IR-inactive m 1 levels of H þ 3 , from which the jovian m 1 ?m 2 difference band emission originates, are populated in thermal equilibrium. The difference band lines thus serve as proxies for the rotational lines in establishing the total auroral H þ 3 column. As a result, the marginally detected 943.953 cm À1 m 1 ?m 2 difference band line implies a vertical H þ 3 column abundance in the range (4.5 ± 3.1) Â 10 12 cm À2 , consistent with the upper limit from the rotational line. The difference band line constrains the vibrational relaxation of the IR-active m 2 fundamental band in Jupiter's aurora to a factor of 4.5-7.5, with an uncertainty ±68%, which supports the model-dependent result of Melin et al.