A multi-diagnostic spectral analysis of penumbral microjets

Abstract

Penumbral microjets (PMJs) are short-lived, jet-like objects found in the penumbra of sunspots. They were first discovered in chromospheric lines and have later also been shown to exhibit signals in transition region (TR) lines. Their origin and manner of evolution is not yet settled. We perform a comprehensive analysis of PMJs through the use of spectral diagnostics that span from photospheric to TR temperatures to constrain PMJ properties. We employed high-spatial-resolution Swedish 1-m Solar Telescope observations in the Ca II 8542 Angstrom and H-alpha lines, IRIS slit-jaw images, and IRIS spectral observations in the Mg II h & k lines, the Mg II 2798.75 Angstrom & 2798.82 Angstrom triplet blend, the C II 1334 Angstrom & 1335 Angstrom lines, and the Si IV 1394 Angstrom & 1403 Angstrom lines. We derived a wide range of spectral diagnostics from these and investigated other secondary phenomena associated with PMJs. We find that PMJs exhibit varying degrees of signal in all of our studied spectral lines. We find low or negligible Doppler velocities and velocity gradients throughout our diagnostics and all layers of the solar atmosphere associated with these. Dark features in the inner wings of H-alpha and Ca II 8542 Angstrom imply that PMJs form along pre-existing fibril structures. We find evidence for upper photospheric heating in a subset of PMJs through emission in the wings of the Mg II triplet lines. There is little evidence for ubiquitous twisting motion in PMJs. There is no marked difference in onset-times for PMJ brightenings in different spectral lines. PMJs most likely exhibit only very modest mass-motions, contrary to earlier suggestions. We posit that PMJs form at upper photospheric or chromospheric heights at pre-existing fibril structures.

arXiv comment26 pages, 18 figures. Accepted for publication in Astronomy & Astrophysics. This version rectifies bad formatting caused by an oversized figure. In the previous version this caused the figure itself and subsequent figures to be misplaced in the text. No other changes beside figure sizing and placement was made. This altered the given page count

References in corpus (27)

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• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
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• Evidence for a Transition Region response to penumbral microjets in sunspots
• A new type of small-scale downflow patches in sunspot penumbrae
• Transition-Region/Coronal Signatures and Magnetic Setting of Sunspot Penumbral Jets: {\it Hinode} (SOT/FG), Hi-C and {\it SDO}/AIA Observations
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• Dynamics of subarcsecond bright dots in the transition region above sunspot and their relation to penumbral micro-jets
• Microjets in the penumbra of a sunspot
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• Penumbral micro-jets at high spatial and temporal resolution
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Cited by in corpus (7)

• The European Solar Telescope
• High-resolution observations of the solar photosphere, chromosphere and transition region. A database of coordinated IRIS and SST observations
• Signatures of ubiquitous magnetic reconnection in the deep atmosphere of sunspot penumbrae
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Automatic detection of Ellerman bombs in the H$\alpha$ line
• Bright Dots and Coronal Plume Formation in Sunspot Penumbra
• Decay of a photospheric transient filament at the boundary of a pore and the chromospheric response