Characterization and formation of on-disk spicules in the Ca II K and Mg II k spectral lines. (arXiv:1910.05533v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bose_S/0/1/0/all/0/1">Souvik Bose</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henriques_V/0/1/0/all/0/1">Vasco M.J. Henriques</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Joshi_J/0/1/0/all/0/1">Jayant Joshi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Voort_L/0/1/0/all/0/1">Luc Rouppe van der Voort</a>

We characterize, for the first time, type-II spicules in Ca II K 3934AA
using the CHROMIS instrument at the Swedish 1-m Solar Telescope. We find that
their line formation is dominated by opacity shifts with the K$_{3}$ minimum
best representing the velocity of the spicules. The K$_{2}$ features are either
suppressed by the Doppler-shifted K$_{3}$ or enhanced via an increased
contribution from the lower layers, leading to strongly enhanced but un-shifted
K$_{2}$ peaks, with widening towards the line-core as consistent with
upper-layer opacity removal via Doppler-shift. We identify spicule spectra in
concurrent IRIS Mg II k 2796AA observations with very similar properties.
Using our interpretation of spicule chromospheric line-formation, we produce
synthetic profiles that match observations.

We characterize, for the first time, type-II spicules in Ca II K 3934AA
using the CHROMIS instrument at the Swedish 1-m Solar Telescope. We find that
their line formation is dominated by opacity shifts with the K$_{3}$ minimum
best representing the velocity of the spicules. The K$_{2}$ features are either
suppressed by the Doppler-shifted K$_{3}$ or enhanced via an increased
contribution from the lower layers, leading to strongly enhanced but un-shifted
K$_{2}$ peaks, with widening towards the line-core as consistent with
upper-layer opacity removal via Doppler-shift. We identify spicule spectra in
concurrent IRIS Mg II k 2796AA observations with very similar properties.
Using our interpretation of spicule chromospheric line-formation, we produce
synthetic profiles that match observations.

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