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A&A manuscript no. (will be inserted by hand later)

Summary: A&A manuscript no.
(will be inserted by hand later)
Your thesaurus codes are:
08 (08.01.3; 08.03.4; 08.12.1; 02.12.1)
Helium lines in late­type dwarfs.
A. C. Lanzafame ? and P. B. Byrne
Armagh Observatory, Armagh BT61 9DG, N. Ireland, UK
Received xxx; accepted xxx
Abstract. We analyse the formation of He I lines in late­type dwarfs by statistical equilibrium (or NLTE radiative
transfer) computations. Atmospheric models for dK (fflEri) and dMe V1005 Ori (=Gl 182) stars are considered. The va­
lidity of the weakly non­uniform approximation for dMe stars established in Lanzafame (1994a) for the lower transition
region of dMe stars implies that streaming particles have virtually no role in the formation of the lines. Comparison
with observations of the He I (10 830 š A) and He I (5 876 š A) lines in the dMe star, V1005 Ori, indicate that it is pos­
sible 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


Source: Armagh Observatory


Collections: Physics