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Current address: Italian Space Agency - Science Data Center, c/o ESA-ESRIN, via Galileo Galilei, 00044 Frascati, Italy.

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...$\bar{g}(T, \nu)$

For simplicity, the estimates in this subsection are obtained for a Gaunt factor set to unity. For the spectra shown in our paper this factor differs slightly from volume to volume.

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