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Helium lines in late­type dwarfs
A.C. Lanzafame and P B Byrne
We analyse the formation of He I lines in late­type dwarfs by statistical equi­
librium (or NLTE radiative transfer) computations. Atmospheric models for
dK (fflEri and dMe V1005 Ori (=Gl 182) stars are considered. The validity of
the weakly non­uniform approximation for dMe stars established in Lanzafame
(1994a) for the lower transition region of dMe stars implies that streaming par­
ticles have virtually no role in the formation of the lines. Comparison with
observations of the HeI (10 830 љ A) lines in the dMe star, V1005 Ori, indicate
that it is possible to reproduce the observed helium lines with a simple model
compatible with other observational constraints. Over­ionisation by coronal
EUV radiation is found to play a minor role in the formation of the triplet lines.
Key words: Stars: atmospheres ­ Stars; chromospheres ­ Stars: late­type ­
Lines: formation
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