6533b855fe1ef96bd12b12ee

RESEARCH PRODUCT

Post-flare Ultraviolet Light Curves Explained with Thermal Instability of Loop Plasma

Fabio RealeFabio RealeEnrico LandiSalvatore Orlando

subject

Sun: flaresPhysicsSolar flareSun: coronaAstrophysics::High Energy Astrophysical PhenomenaAstronomy and AstrophysicsAstrophysicsPlasmaSun: UV radiationLight curvemedicine.disease_causelaw.inventionSettore FIS/05 - Astronomia E AstrofisicainstabilitiesSpace and Planetary SciencelawExtreme ultravioletPhysics::Space PhysicsUltraviolet lightmedicineAstrophysics::Solar and Stellar Astrophysicscorona ; Sun: flares ; Sun: UV radiation [instabilities ; Sun]UltravioletLine (formation)Flare

description

In the present work, we study the C8 flare that occurred on 2000 September 26 at 19:49 UT and observed by the Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation spectrometer from the beginning of the impulsive phase to well beyond the disappearance in the X-rays. The emission first decayed progressively through equilibrium states until the plasma reached 2-3 MK. Then, a series of cooler lines, i.e., Ca X, Ca VII, Ne VI, O IV, and Si III (formed in the temperature range log T = 4.3-6.3 under equilibrium conditions), are emitted at the same time and all evolve in a similar way. Here, we show that the simultaneous emission of lines with such a different formation temperature is due to thermal instability occurring in the flaring plasma as soon as it has cooled below ~2 MK. We can qualitatively reproduce the relative start time of the light curves of each line in the correct order with a simple (and standard) model of a single flaring loop. The agreement with the observed light curves is greatly improved, and a slower evolution of the line emission is predicted, if we assume that the model loop consists of an ensemble of subloops or strands heated at slightly different times. Our analysis can be useful for flare observations with the Solar Dynamics Observatory/Extreme ultraviolet Variability Experiment.

10.1088/0004-637x/746/1/18http://hdl.handle.net/10447/73023