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Intermittent Coronal Loop Oscillations by Random Energy Releases  

Cesar A. Mendoza-Briceno   Submitted: 2005-10-24 19:49

High resolution observations by the SoHO and TRACE spacecrafts have confirmed the existence of oscillations and waves of coronal loops. In a recent work, Mendoza-Brice~no et al. (2005) studied the heating response of coronal plasma to energy pulses randomly distributed in time and space along coronal loops. In this paper we focus on the oscillatory patterns and other features, like cool gas blobs travelling along the loop, during the evolution of spatio-temporal randomly heated flux tubes in the corona. The nature of these oscillatory patterns is investigated by using wavelet analysis. Periodic features, like wave packets, with periods of 150-220 s, 500-600 s and 800-1000 s are found. It is also found the periods increase with the length of the loop and decrease with the length of loop segment of injection of the pulses along the loop. On the other hand, the randomly driven intermittent cool plasma blobs that propagate from one footpoint to another are analysed. Although plenty of coronal loop oscillations are detected by the cohort of the current high-resolution satellites there are more controversial observational evidences of the found cold plasma blobs.

Authors: Cesar A. Mendoza-Briceno and Robert Erdelyi.
Projects: None

Publication Status: Submitted to Astronomy and Astrophysics
Last Modified: 2005-10-24 19:49
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Coronal mass transfer in interbinary loops  

Cesar A. Mendoza-Briceno   Submitted: 2005-05-05 03:25

We consider the transfer of coronal mass between the members of a detached binary system along interconnecting rigid magnetic loops. We show that the asymmetry in the gravitational potential drives a flow from the star closer to fill its Roche lobe towards the other star. The loop base pressures, flow velocities and mass fluxes are not externally imposed but are a result of the heating rate along the loop. As the loop heating increases, the base pressures and mass transfer rates increase and the Mach number decreases. If the heating is not uniformly distributed along the loop, but is instead concentrated near one of the stars, then the mass transfer rate either increases or it decreases, and even changes direction, depending on which star the heating is concentrated on. We also discuss the effect of choosing different boundary conditions. Our model predicts mass transfer rates in reasonable agreement with existing observational estimates, but fails to explain the presence of chromospheric material detected between the stars. Additionally, the differential emission measure profile of the loop models is calculated and it is found to be higher in the loop leg close to the secondary star.

Authors: J. M. Ferreira & C. A. Mendoza-BriceƱo
Projects: None

Publication Status: A&A, 2005, 433, 1055-1061
Last Modified: 2005-05-05 03:25
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Catastrophic cooling of impulsively heated coronal loops  

Cesar A. Mendoza-Briceno   Submitted: 2004-11-01 03:57

The physical mechanisms that cause the heating of the solar corona are still far from being completely understood. However, recent highly-resolved observations with the current solar missions have thrown clear evidence for frequent and very localized heating events near the chromosphere, which may be responsible for the observable high temperatures of the coronal plasma. In this paper, we perform one-dimensional hydrodynamic simulations of the evolution of a hypothetical loop model undergoing impulsive heating through the release of localized Gaussian energy pulses near the loop's footpoints.We find that when a discrete number of randomly spaced pulses is released, the loop heats up and stays at coronal temperatures for the whole duration of the impulsive heating stage provided that the elapsing time between successive heat injections is lesssim 215 s. For elapsing times longer than this critical value, coronal temperatures can no longer be maintained at the loop apex in spite of continued impulsive heating. As a result, the loop apex cools down catastrophically well below the initial state, reaching chromospheric temperatures (sim 104 K) and leading to the typical hot-cool temperature profile characteristic of a cool condensation. For a large number of pulses (up to sim 1000) having a fully random spatio-temporal distribution, the variation of the temperature along the loop is highly sensitive to the spatial distribution of the heating. As long as the heating concentrates more and more at the loop's footpoints, the temperature variation is seen to make a transition from that of a uniformly heated loop to a flat, isothermal profile along the loop length. Concentration of the heating at the footpoints also results in the more frequent appearance of rapid and significant depressions of the apex temperature during the loop evolution, most of them ranging from sim 1.5 imes 106 to sim 104 K and lasting from about 3 to 10 minutes. This behavior bears a tight relation with the strong variability of coronal loops inferred from {it SOHO} observations in active regions of the solar atmosphere.

Authors: Cesar A. Mendoza-Briceno, Leonardo Di G. Sigalotti & Robert Erdelyi
Projects:

Publication Status: ApJ, 2005, 624, 1080-1092 (in press)
Last Modified: 2005-05-09 03:18
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Catastrophic cooling of impulsively heated coronal loops  

Cesar A. Mendoza-Briceno   Submitted: 2004-11-01 03:57

The physical mechanisms that cause the heating of the solar corona are still far from being completely understood. However, recent highly-resolved observations with the current solar missions have thrown clear evidence for frequent and very localized heating events near the chromosphere, which may be responsible for the observable high temperatures of the coronal plasma. In this paper, we perform one-dimensional hydrodynamic simulations of the evolution of a hypothetical loop model undergoing impulsive heating through the release of localized Gaussian energy pulses near the loop's footpoints.We find that when a discrete number of randomly spaced pulses is released, the loop heats up and stays at coronal temperatures for the whole duration of the impulsive heating stage provided that the elapsing time between successive heat injections is lesssim 215 s. For elapsing times longer than this critical value, coronal temperatures can no longer be maintained at the loop apex in spite of continued impulsive heating. As a result, the loop apex cools down catastrophically well below the initial state, reaching chromospheric temperatures (sim 104 K) and leading to the typical hot-cool temperature profile characteristic of a cool condensation. For a large number of pulses (up to sim 1000) having a fully random spatio-temporal distribution, the variation of the temperature along the loop is highly sensitive to the spatial distribution of the heating. As long as the heating concentrates more and more at the loop's footpoints, the temperature variation is seen to make a transition from that of a uniformly heated loop to a flat, isothermal profile along the loop length. Concentration of the heating at the footpoints also results in the more frequent appearance of rapid and significant depressions of the apex temperature during the loop evolution, most of them ranging from sim 1.5 imes 106 to sim 104 K and lasting from about 3 to 10 minutes. This behavior bears a tight relation with the strong variability of coronal loops inferred from {it SOHO} observations in active regions of the solar atmosphere.

Authors: Cesar A. Mendoza-Briceno, Leonardo Di G. Sigalotti & Robert Erdelyi
Projects: None

Publication Status: ApJ, 2005, 624, 1080-1092
Last Modified: 2005-05-09 03:20
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Abstracts by Author
Intermittent Coronal Loop Oscillations by Random Energy Releases
Coronal mass transfer in interbinary loops
Catastrophic cooling of impulsively heated coronal loops
Catastrophic cooling of impulsively heated coronal loops

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