Volume 521, October 2010
Herschel/HIFI: first science highlights
Article Number L35
Number of page(s) 5
Section Letters
Published online 01 October 2010

Online Material

Appendix A:

The rotational diagram in Fig. A.1 is complemented with ground-based data for the frequency range 300-400 GHz observed at the CSO with comparable beam size by Phillips et al. (1992). The non-detection at 307 MHz is surprising, but possibly an effect of optical depth. The data in Fig. A.1, except 307 GHz, are well fitted by a single rotational temperature of 239 K, suggesting that the observed levels are populated according to an exponential distribution. The derived temperature and column density infer an optical depth of $\tau < 0.1$ for all lines except at 307 GHz. The fitted line (dashed) corresponds to a column density of $8.5 (\pm 2)\times 10^{13}$ cm-2, consistent with the value derived by Phillips et al. (1992). This leads to a beam averaged H3O+ abundance of $4.2 (\pm 1)\times 10^{-10}$ relative to H, to be compared with the theoretical value of $4 \times 10^{-10}$ reported by Bruderer et al. (2010a).

\end{figure} Figure A.1:

Rotational diagram of H3O+. Numbers indicate the frequencies in GHz of the observed lines.

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