We analyse the formation of HeI lines in late-type dwarfs by statistical equilibrium (or NLTE radiative transfer) computations. Atmospheric models for a dK (epsilon Eri) and a dMe (V 1005 Ori = G1 182) stars are considered. The validity of the weakly non-uniform 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 HeI(10 830 Angstrom) and HeI(5 876 Angstrom) lines in the dMe star, V 1005 Ori, indicate that it is possible to reproduce the observed helium lines with a simple model compatible with other observational constraints. Over-ionisation by coronal EUV radiation is found to play a minor role in the formation of the triplet lines.
HELIUM LINES IN LATE-TYPE DWARFS
LANZAFAME, Alessandro Carmelo;
1995-01-01
Abstract
We analyse the formation of HeI lines in late-type dwarfs by statistical equilibrium (or NLTE radiative transfer) computations. Atmospheric models for a dK (epsilon Eri) and a dMe (V 1005 Ori = G1 182) stars are considered. The validity of the weakly non-uniform 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 HeI(10 830 Angstrom) and HeI(5 876 Angstrom) lines in the dMe star, V 1005 Ori, indicate that it is possible to reproduce the observed helium lines with a simple model compatible with other observational constraints. Over-ionisation by coronal EUV radiation is found to play a minor role in the formation of the triplet lines.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
