Ca II 8542 Å brightenings induced by a solar microflare

Abstract

We study small-scale brightenings in Ca II 8542 Å line-core images to determine their nature and effect on localized heating and mass transfer in active regions. High-resolution 2D spectroscopic observations of an active region in the Ca II 8542 Å line were acquired with the GFPI attached to the 1.5-meter GREGOR telescope. Inversions of the spectra were carried out using NICOLE. We identified three brightenings of sizes up to 2"x2". We found evidence that the brightenings belonged to the footpoints of a microflare (MF). The properties of the observed brightenings disqualified the scenarios of Ellerman bombs or IRIS bombs. However, this MF shared some common properties with flaring active-region fibrils or flaring arch filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric and coronal layers according to the AIA channels, and (2) both show flaring arches with lifetimes of about 3.0-3.5 min and lengths of about 20". The inversions revealed heating by 600 K at the footpoint location in the ambient chromosphere during the impulsive phase. Connecting the footpoints, a dark filamentary structure appeared in the Ca II line-core images. Before the start of the MF, the spectra of this structure already indicated average blueshifts, meaning upward motions of the plasma along the LOS. During the impulsive phase, these velocities increased up to -2.2 km/s. Downflows dominated at the footpoints. However, in the upper photosphere, slight upflows occurred during the impulsive phase. Hence, bidirectional flows are present in the footpoints of the MF. Conclusions: We detected Ca II brightenings that coincided with the footpoint location of an MF. The MF event led to a rise of plasma in the upper photosphere, both before and during the impulsive phase. Excess mass, previously raised to at most chromospheric layers, slowly drained downward along arches toward the footpoints of the MF.

arXiv commentAccepted for publication in Astronomy & Astrophysics, 13 pages, 6 figures, 1 online movie

References in corpus (22)

• The Interface Region Imaging Spectrograph (IRIS)
• Hot Explosions in the Cool Atmosphere of the Sun
• RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
• An Open Source, Massively Parallel Code for Non-LTE Synthesis and Inversion of Spectral Lines and Zeeman-induced Stokes Profiles
• Ellerman bombs at high resolution III. Simultaneous observations with IRIS and SST
• Physical Properties of a Sunspot Chromosphere with Umbral Flashes
• Are IRIS bombs connected to Ellerman bombs?
• Ellerman Bombs at high resolution: II. Visibility, triggering and effect on upper atmosphere
• Ellerman bombs: fallacies, fads, usage
• Non-local thermodynamic equilibrium inversions from a 3D MHD chromospheric model
• Spectropolarimetric capabilities of Ca II 8542 A line
• H-alpha features with hot onsets. I. Ellerman bombs
• Magnetic Flux Cancellation in Ellerman Bombs
• Spectro-polarimetric observations and non-LTE Modeling of Ellerman bombs
• UV spectra, bombs, and the solar atmosphere
• The GREGOR Fabry-Pérot Interferometer
• Microflares and Hot Component in Solar Active Regions
• Statistical Analysis of Small Ellerman Bomb Events
• Observations and NLTE modeling of Ellerman bombs
• The effect of isotopic splitting on the bisector and inversions of the solar Ca II 854.2 nm line
• Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare
• Fitting peculiar spectral profiles in He I 10830 Å absorption features

Cited by in corpus (4)

• High-Cadence Imaging and Imaging Spectroscopy at the GREGOR Solar Telescope - A Collaborative Research Environment for High-Resolution Solar Physics
• Accurately constraining velocity information from spectral imaging observations using machine learning techniques
• Chromospheric velocities in an M3.2 flare using He I 1083.0 nm and Ca II 854.2 nm
• Tracking downflows from the chromosphere to the photosphere in a solar arch filament system