2004MNRAS.354...71A -
Mon. Not. R. Astron. Soc., 354, 71-80 (2004/October-2)
The effects of X-ray photoionization and heating on the structure of circumstellar discs.
ALEXANDER R.D., CLARKE C.J. and PRINGLE J.E.
Abstract (from CDS):
We present the results of a theoretical study investigating the effects of photoionization and heating by X-rays on discs around low-mass stars. In particular, we address the question of whether or not X-rays can drive a disc wind. First, we construct a one-dimensional `quasi-hydrostatic' model, which solves for the vertical structure introduced by X-ray heating. We consider uniform X-ray illumination of the disc, but the X-ray fluxes required to heat the disc significantly are much greater than those seen by recent observations. When the model is extended to consider heating from a central X-ray source, we find that the one-dimensional model is only valid very close to the star. We extend our analysis to consider a simple two-dimensional model, treating the disc as a two-layered structure and solving for its density profile self-consistently. For T Tauri stars, we are able to set a crude upper limit on the mass-loss rate that can be driven by X-ray photoevaporation, with a value of ≃10–13g/cm2/s. Our model is designed to maximize this value, and most likely overestimates it significantly. However, we still find a mass-loss rate which is less than that found in studies of ultraviolet photoevaporation. We conclude that in the presence of a significant ultraviolet field, X-ray driven disc winds are unlikely to play a significant role in the evolution of discs around low-mass stars.
Abstract Copyright:
2004 RAS
Journal keyword(s):
accretion, accretion discs - circumstellar matter - planetary systems: protoplanetary discs - stars: pre-main-sequence - X-rays: stars
Simbad objects:
4
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