Volume 638, June 2020
|Number of page(s)||26|
|Section||The Sun and the Heliosphere|
|Published online||11 June 2020|
A multi-diagnostic spectral analysis of penumbral microjets⋆
Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
2 Rosseland Centre for Solar Physics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
Accepted: 15 April 2020
Context. 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.
Aims. We perform a comprehensive analysis of PMJs through the use of spectral diagnostics that span from photospheric to TR temperatures to constrain PMJ properties.
Methods We employed high-spatial-resolution Swedish 1-m Solar Telescope observations in the Ca II 8542 Å and H α lines, IRIS slit-jaw images, and IRIS spectral observations in the Mg II h & k lines, the Mg II 2798.75 Å & 2798.82 Å triplet blend, the C II 1334 Å & 1335 Å lines, and the Si IV 1394 Å & 1403 Å lines. We derived a wide range of spectral diagnostics from these and investigated other secondary phenomena associated with PMJs.
Results. 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 α and Ca II 8542 Å 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.
Conclusions. 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.
Key words: Sun: atmosphere / Sun: chromosphere / Sun: photosphere / sunspots / Sun: magnetic fields
Movies associated to Appendix B are available at https://www.aanda.org
© ESO 2020
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.