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Dependence of the He/H8 emission ratio on brightness, temperature, and structuring of prominences

We investigate the dependence of the He/H8 emission ratio on kinetic temperature and total Balmer brightness. The line pair He\,{\sc i}\,3888\,Å and H$_8$\,3889 has been observed simultaneously with the Ca II 8498 line in a number of quiescent prominences. The He/H8 emission ratio R is found to cover defined parts of a general anti-relation with the total H8 emission, depending on the kinetic temperature, T_kin, of the individual prominence: High H8 brightness is related to small R and T_kin values, and preferably occurs in prominences with a less significant fine-structure.