The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations

Abstract

The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding rocket payload built to study the crucial interface between the solar chromosphere and the corona by observing the strongest line in the solar spectrum, the Ly-a line at 1216 Å. In two flights, VAULT succeeded in obtaining the first ever sub-arcsecond (0.5") images of this region with high sensitivity and cadence. Detailed analyses of those observations have contributed significantly to new ideas about the nature of the transition region. Here, we present a broad overview of the Ly-a atmosphere as revealed by the VAULT observations, and bring together past results and new analyses from the second VAULT flight to create a synthesis of our current knowledge of the high-resolution Ly-a Sun. We hope that this work will serve as a good reference for the design of upcoming Ly-a telescopes and observing plans.

28 pages, 11 figures

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• Filament Channel Formation Via Magnetic Helicity Condensation
• H-alpha features with hot onsets III. Fibrils in Lyman-alpha and with ALMA
• Chromospheric backradiation in ultraviolet continua and Halpha
• CLASP Constraints on the Magnetization and Geometrical Complexity of the Chromosphere-Corona Transition Region
• The Mechanism for the Energy Buildup Driving Solar Eruptive Events
• The Hanle effect of Ly$\alpha$ in an MHD model of the Solar Transition Region
• On the inversion of the scattering polarization and the Hanle effect signals in the hydrogen Lyman-$\alpha$ line
• First high-resolution images of the Sun in the 2796 Å Mg II k line
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• Comparison of Solar Fine Structure Observed Simultaneously in Ly-α and Mg II h
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• Stereoscopic Measurements of Coronal Doppler Velocities
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