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The helium line formation in late-type stars - I. The quiet sun

1989; Oxford University Press; Volume: 240; Issue: 1 Linguagem: Inglês

10.1093/mnras/240.1.23

1365-2966

Natalie M. Batalha, R. de la Reza,

Solar and Space Plasma Dynamics

The formation of helium lines and continua in an atmospheric model representing the medium quiet sun has been investigated considering principally the influence of: (i) changes in the temperature gradient at Transition Region (TR); (ii) the coronal radiation and (iii) the overlapping of He II Ly α at 304 Å and the continuum radiation of He I at |$\lambda\leqslant504$| Å. By diminishing the thermal gradient in the Transition Region a large part of the helium observations are reproduced. This is the case for the He II resonance λ 304 line which is collisionally controlled and is formed at |$1.0 \times {10}^{5}\,\text{K},$| and the He I resonance line at 584 Å which is also collisionally controlled but is formed at deeper layers with a mean temperature of |$2.5 \times {10}^{4}\,\text{K}.$| The He II continuum at 228 Å as well as the Lβ 1ine at 256 Å can be adjusted to observations if a characteristic solar coronal flux is incident on the optimized Transition Region. No reasonable coronal radiation can account for the observed He II line or continuum intensities alone.