Thermal conduction and modeling of static stellar coronal loops |
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| Authors: | A Ciaravella G Peres S Serio |
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| Institution: | (1) Istituto di Astronomia, Università Palermo, Italy;(2) IAIF/CNR, Palermo, Italy;(3) Osservatorio Astrofisico di Catania, Italy;(4) Osservatorio Astronomico di Palermo, Italy |
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| Abstract: | We have modeled stellar coronal loops in static conditions for a wide range of loop length, plasma pressure at the base of the loop and stellar surface gravity, so as to describe physical conditions that can occur in coronae of stars ranging from low mass dwarfs to giants as well as on a significant fraction of the Main-Sequence stars.Three alternative formulations of heat conduction have been used in the energy balance equation, depending on the ratio
0/L
Tbetween electron mean free path and temperature scale height: Spitzer's formulation for
0/L
Tless than 2 × 10–3, the Luciani, Mora, and Virmont non-local formulation for
0/L
Tbetween 2 × 10–3 and 6.67 × 10–3 and the limited free-streaming formulation for
0/L
Tlarger than 6.67 × 10–3.We report the characteristics of all loop models studied, and present examples to illustrate how the temperature and density stratification can be drastically altered by the different conductivity regimes. Significant differences are evident in the differential emission measure distribution vs temperature, an important observable quantity. We also show how physical conditions of coronal plasma, and in particular thermal conduction, change with stellar surface gravity.We have found that, for fixed loop length and stellar gravity, a minimum of loop-top plasma temperature occurs, corresponding to the highest value of base plasma pressure for which the limited free-streaming conduction occurs. This value of temperature satisfies the appropriate scalingT  10–9
L g, in cgs units. |
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| Keywords: | |
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