Inferring chromospheric velocities in an M3.2 flare using He I 1083.0 nm and Ca II 854.2 nm

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Fig. 2.

Response functions of the Ca II 8542 Å spectral line to changes in the LOS velocity. The lower panel corresponds to a pixel within the bright flare, at the ribbon front at coordinates $x, y = 33 \binom{″}{\cdot} 9, 44 \binom{″}{\cdot} 6$ $x,{{\mathit {y}}} = 33\mbox {${{{\prime\prime \atop \cdot }} }$}9,44\mbox {${{{\prime\prime \atop \cdot }} }$}6$ (see light blue cross in Fig. 1f), whereas the upper panel shows the RF in a quiet-Sun pixel (pink cross in Fig. 1f at $x, y = 35 \binom{″}{\cdot} 0, 75 \binom{″}{\cdot} 2$ $x,{{\mathit {y}}} = 35\mbox {${{{\prime\prime \atop \cdot }} }$}0,75\mbox {${{{\prime\prime \atop \cdot }} }$}2$ ). The RFs are normalized to their maximum absolute value and saturated between ±0.7 to enhance the weaker areas. The corresponding observed intensity profile is shown in the upper right corner of each panel and extends over the same spectral range as the RF. The horizontal dashed lines mark the optical depths at log τ=−2.0, −3.0, and −3.5.

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