New Insights into White-Light Flare Emission from Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
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- 作者：Adam F. Kowalski ; S. L. Hawley ; M. Carlsson ; J. C. Allred ; H. Uitenbroek…
- 关键词：Flares ; dynamics ; Flares ; energetic particles ; Flares ; impulsive phase ; Flares ; models ; Flares ; spectrum ; Flares ; white ; light
- 刊名：Solar Physics
- 出版年：2015
- 出版时间：December 2015
- 年：2015
- 卷：290
- 期：12
- 页码：3487-3523
- 全文大小：2,082 KB
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S. L. Hawley (3)
M. Carlsson (4)
J. C. Allred (2)
H. Uitenbroek (5)
R. A. Osten (6)
G. Holman (2)
1. Department of Astronomy, University of Maryland, College Park, MD, 20742, USA
2. NASA Goddard Space Flight Center, Heliophysics Science Division, Code 671, 8800 Greenbelt Rd., Greenbelt, MD, 20771, USA
3. Department of Astronomy, University of Washington, Box 351580, Seattle, WA, 98195, USA
4. Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, 0315, Oslo, Norway
5. National Solar Observatory, Sacramento Peak, P.O. Box 62, Sunpsot, NM, 88349, USA
6. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218, USA - 刊物类别：Physics and Astronomy
- 刊物主题：Physics
Astronomy
Extraterrestrial Physics and Space Sciences
Astrophysics - 出版者：Springer Netherlands
- ISSN：1573-093X
文摘
The heating mechanism at high densities during M-dwarf flares is poorly understood. Spectra of M-dwarf flares in the optical and near-ultraviolet wavelength regimes have revealed three continuum components during the impulsive phase: 1) an energetically dominant blackbody component with a color temperature of \(T\approx10^{4}~\mbox{K}\) in the blue-optical, 2) a smaller amount of Balmer continuum emission in the near-ultraviolet at \(\lambda\le3\,646\) ?, and 3) an apparent pseudo-continuum of blended high-order Balmer lines between \(\lambda=3\,646\) ? and \(\lambda\approx3\,900\) ?. These properties are not reproduced by models that employ a typical “solar-type-flare heating level of \({\le}\,10^{11}~\mbox{erg}\,\mbox{cm}^{-2}\,\mbox{s}^{-1}\) in nonthermal electrons, and therefore our understanding of these spectra is limited to a phenomenological three-component interpretation. We present a new 1D radiative-hydrodynamic model of an M-dwarf flare from precipitating nonthermal electrons with a high energy flux of \(10^{13}~\mbox{erg}\,\mbox{cm}^{-2}\,\mbox{s}^{-1}\). The simulation produces bright near-ultraviolet and optical continuum emission from a dense (\(n>10^{15}~\mbox{cm}^{-3}\)), hot (\(T \approx12\,000\,\mbox{--}\,13\,500~\mbox{K}\)) chromospheric condensation. For the first time, the observed color temperature and Balmer jump ratio are produced self-consistently in a radiative-hydrodynamic flare model. We find that a \(T\approx10^{4}~\mbox{K}\) blackbody-like continuum component and a low Balmer jump ratio result from optically thick Balmer (\(\infty\rightarrow n=2\)) and Paschen recombination (\(\infty\rightarrow n=3\)) radiation, and thus the properties of the flux spectrum are caused by blue (\(\lambda\approx4\,300\) ?) light escaping over a larger physical depth range than by red (\(\lambda\approx6\,700\) ?) and near-ultraviolet (\(\lambda\approx3\,500\) ?) light. To model the near-ultraviolet pseudo-continuum previously attributed to overlapping Balmer lines, we include the extra Balmer continuum opacity from Landau–Zener transitions that result from merged, high-order energy levels of hydrogen in a dense, partially ionized atmosphere. This reveals a new diagnostic of ambient charge density in the densest regions of the atmosphere that are heated during dMe and solar flares. Keywords Flares, dynamics Flares, energetic particles Flares, impulsive phase Flares, models Flares, spectrum Flares, white-light