Stability of thermal structures with an internal heating source
N. Sánchez*, E. López**
* Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain, e–mail: nestor@iaa.es
** Departamento de Física y Matemáticas, Universidad Nacional Experimental Francisco de Miranda, Coro, Venezuela.
Recibido el 20 de febrero de 2007 ]]> Aceptado el 25 de febrero de 2008
Abstract
We study the thermal equilibrium and stability of isobaric, spherical structures having a radiation source located at their center. The thermal conduction coefficient, external heating and cooling rates are represented as power laws of the temperature. The internal heating decreases with distance from the source r approximately as ~ exp(–τ)/r2, τ being the optical depth. We find that the influence of the radiation source is important only in the central region, but its effect is enough to make the system thermally unstable above a certain threshold central temperature. This threshold temperature decreases as the internal heating efficiency increases, but, otherwise, it does not depend on the structure size. Our results suggest that a solar–like star migrating into a diffuse interstellar region may destabilize the surrounding medium.
Keywords: Hydrodynamics; instabilities; interstellar medium.
Resumen
En este trabajo estudiamos el equilibrio térmico y la estabilidad de estructuras isobáricas y esféricas que tienen una fuente de radiación en su centro. La conducción térmica y las tasas de calentamiento externo y enfriamiento son representadas como leyes de potencia de la temperatura. El calentamiento interno disminuye con la distancia a la fuente r aproximadamente como ~ exp(– τ)/r2, siendo τ la profundidad óptica. Los resultados indican que la influencia de la fuente de radiación es importante solamente en la región central, pero su efecto es suficiente para que el sistema se vuelva térmicamente inestable por encima de una cierta temperatura umbral en el centro. Esta temperatura umbral disminuye a medida que la eficiencia del calentamiento interno aumenta, pero por otro lado la misma no depende del tamaño de la estructura. Nuestros resultados sugieren que una estrella de tipo solar que migre a través del medio interestelar difuso puede llegar a desestabilizarlo.
Descriptores: Hidrodinámica; inestabilidades; medio interestelar.
]]> PACS: 47.50.Gj; 95.30.Lz; 98.38.Am
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Acknowledgments
We are very grateful to the anonymous referee for the critical and constructive report, which improved this paper. N.S. acknowledges financial support from MEC of Spain through grant AYA2007–64052.
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