Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a...101..241c&link_type=abstract
Astronomy and Astrophysics, vol. 101, no. 2, Aug. 1981, p. 241-246. Research supported by the Max-Planck-Gesellschaft zur Foerd
Astronomy and Astrophysics
Astrophysics
2
Calcium, Infrared Spectra, Metallic Stars, Mira Variables, Stellar Spectra, Stellar Spectrophotometry, Variable Stars, Abundance, Electron Density (Concentration), Electron Energy, Emission Spectra, H Alpha Line, Metal Ions, Red Giant Stars, Shock Waves, Stellar Atmospheres
Scientific paper
The Ca II infrared triplet has been observed in 22 S-type Mira stars of different periods at various phases of the light cycle. The observations were obtained with a spectrograph equipped with a single-stage image intensifier tube, electrostatically focused, using an S-20 extended-red photocathode. The objects were observed in two distinct spectral regions, in the red (5800-7800 A) and near-infrared (6800-8700 A), with a reciprocal linear dispersion of 87 A/mm, and an actual resolution of about 5 A. The spectrograms were measured with a Grant machine in its densitometer mode and reduced on a computer. The Ca II infrared emission lines appear around a phase of 0.80, i.e., close to the phase when hydrogen emission is observed first, and much earlier than the Ca II H and K emission lines. The differences in the radial velocity of the Ca II infrared emission lines with respect to the absorption line spectrum are much smaller than those of the Ca II H and K lines. It is concluded that the emission originates in a hot layer, created deep in the atmosphere by a shock front, which moves upwards as the phase advances. A shock velocity smaller than 45 km/s is compatible with the observations and predicts the observed correlation of the strength of the Ca II emission lines with the period and spectral type at a maximum.
Contadakis M. E.
Solf Josef
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