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|Title:||Optical Spectral Observations of a Flickering White-light Kernel in a C1 Solar Flare||Authors:||Kowalski, Adam F.
|Issue Date:||2015||Journal:||THE ASTROPHYSICAL JOURNAL||Number:||798||Issue:||2||First Page:||107||Abstract:||We analyze optical spectra of a two-ribbon, long-duration C1.1 flare that occurred on 2011 August 18 within AR 11271 (SOL2011-08-18T15:15). The impulsive phase of the flare was observed with a comprehensive set of space-borne and ground-based instruments, which provide a range of unique diagnostics of the lower flaring atmosphere. Here we report the detection of enhanced continuum emission, observed in low-resolution spectra from 3600 Å to 4550 Å acquired with the Horizontal Spectrograph at the Dunn Solar Telescope. A small, <=0.''5 (1015 cm2) penumbral/umbral kernel brightens repeatedly in the optical continuum and chromospheric emission lines, similar to the temporal characteristics of the hard X-ray variation as detected by the Gamma-ray Burst Monitor on the Fermi spacecraft. Radiative-hydrodynamic flare models that employ a nonthermal electron beam energy flux high enough to produce the optical contrast in our flare spectra would predict a large Balmer jump in emission, indicative of hydrogen recombination radiation from the upper flare chromosphere. However, we find no evidence of such a Balmer jump in the bluemost spectral region of the continuum excess. Just redward of the expected Balmer jump, we find evidence of a "blue continuum bump" in the excess emission which may be indicative of the merging of the higher order Balmer lines. The large number of observational constraints provides a springboard for modeling the blue/optical emission for this particular flare with radiative-hydrodynamic codes, which are necessary to understand the opacity effects for the continuum and emission line radiation at these wavelengths.||Acknowledgments:||The research has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under agreement 606862 (F-CHROMA).||URI:||http://hdl.handle.net/20.500.12386/26402||URL:||https://iopscience.iop.org/article/10.1088/0004-637X/798/2/107||ISSN:||0004-637X||DOI:||10.1088/0004-637X/798/2/107||Bibcode ADS:||2015ApJ...798..107K||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Sep 20, 2020
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