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Table 2

Observational features of the Ca IR triplet in the star sample.

ϕ interval Small (P < 10d) Medium (P ≈ 10d) Long (P > 10d)
0.9–0.3 Quiescent profiles: The atmospheric layers are moving outward. Quiescent profiles Schwarzschild mechanism: Infalling chromosphere layers are collapsing onto the emerging shock causing a double absorption profile P Cygni profile: The main shock front is still propagating and progressively leaves Ca IR layers, entering in outermost Hα layers.

0.3–0.6 Quiescent profiles Inverse P Cygni profile: Emission from supersonic infalling layers. Quiescent profiles

0.6–1.0 Inverse P Cygni profile: A weak emission is observable in several short periods. Profile enlargement: The profiles are importantly wider due to turbulences during atmosphere collision. Line doubling: Enlargement of the line profile which is possibly a double profile due to a Schwarzschild scenario. P Cygni profile: It appears when the main shock from the previous cycle is high enough in the chromosphere. Inverse P Cygni profile: Emission from supersonic infalling layers. Transition phase: From 0.9 to 1.0 the latter emission progressively disappears. Schwarzschild mechanism initiates.

Notes. The table is divided into pulsation periods (columns) and phase interval (rows). In Fig. 6 we represent the mean features observed in each phase interval.

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