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Simultaneous Extreme-Ultraviolet Explorer and Optical Observations of Ad Leonis: Evidence for Large Coronal Loops and the Neupert Effect in Stellar FlaresWe report on the first simultaneous Extreme-Ultraviolet Explorer (EUVE) and optical observations of flares on the dMe flare star AD Leonis. The data show the following features: (1) Two flares (one large and one of moderate size) of several hours duration were observed in the EUV wavelength range; (2) Flare emission observed in the optical precedes the emission seen with EUVE; and (3) Several diminutions (DIMs) in the optical continuum were observed during the period of optical flare activity. To interpret these data, we develop a technique for deriving the coronal loop length from the observed rise and decay behavior of the EUV flare. The technique is generally applicable to existing and future coronal observations of stellar flares. We also determine the pressure, column depth, emission measure, loop cross-sectional area, and peak thermal energy during the two EUV flares, and the temperature, area coverage, and energy of the optical continuum emission. When the optical and coronal data are combined, we find convincing evidence of a stellar 'Neupert effect' which is a strong signature of chromospheric evaporation models. We then argue that the known spatial correlation of white-light emission with hard X-ray emission in solar flares, and the identification of the hard X-ray emission with nonthermal bremsstrahlung produced by accelerated electrons, provides evidence that flare heating on dMe stars is produced by the same electron precipitation mechanism that is inferred to occur on the Sun. We provide a thorough picture of the physical processes that are operative during the largest EUV flare, compare and contrast this picture with the canonical solar flare model, and conclude that the coronal loop length may be the most important factor in determining the flare rise time and energetics.
Document ID
19960018486
Document Type
Reprint (Version printed in journal)
Authors
Hawley, Suzanne L.
(Michigan State Univ. East Lansing, MI United States)
Fisher, George H.
(California Univ. Berkeley, CA United States)
Simon, Theodore
(Hawaii Univ. Honolulu, HI United States)
Cully, Scott L.
(California Univ. Berkeley, CA United States)
Deustua, Susana E.
(Lawrence Livermore National Lab. Livermore, CA United States)
Jablonski, Marek
(Oslo Univ. Norway)
Johns-Krull, Christopher
(McDonald Observatory Austin, TX United States)
Pettersen, Bjorn R.
(Norwegian Mapping Authority Honefoss, Norway)
Smith, Verne
(Texas Univ. Austin, TX United States)
Spiesman, William J.
(McDonald Observatory Austin, TX United States)
Valenti, Jeffrey
(Colorado Univ. Boulder, CO United States)
Date Acquired
September 6, 2013
Publication Date
November 1, 1995
Subject Category
Astronomy
Report/Patent Number
NAS 1.26:200728
NASA-CR-200728
Funding Number(s)
CONTRACT_GRANT: NAG5-2275
CONTRACT_GRANT: NSF AST-94-57455
CONTRACT_GRANT: NAS5-27555
CONTRACT_GRANT: NSF AST-92-18085
CONTRACT_GRANT: NAGw-3429
CONTRACT_GRANT: W-7405-eng-48
CONTRACT_GRANT: HF-1017.01-91A
Distribution Limits
Public
Copyright
Public Use Permitted.

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