Аннотация
The strong X-ray irradiation from young solar-type stars may play a crucial
role in the thermodynamics and chemistry of circumstellar discs, driving their
evolution in the last stages of disc dispersal as well as shaping the
atmospheres of newborn planets. In this paper we study the influence of stellar
mass on circumstellar disc mass-loss rates due to X-ray irradiation, extending
our previous study of the mass-loss rate's dependence on the X-ray luminosity
and spectrum hardness. We focus on stars with masses between 0.1 and 1 Solar
mass, which are the main target of current and future missions to find
potentially habitable planets. We find a linear relationship between the
mass-loss rates and the stellar masses when changing the X-ray luminosity
accordingly with the stellar mass. This linear increase is observed also when
the X-ray luminosity is kept fixed because of the lower disc aspect ratio which
allows the X-ray irradiation to reach larger radii. We provide new analytical
relations for the mass-loss rates and profiles of photoevaporative winds as a
function of the stellar mass that can be used in disc and planet population
synthesis models. Our photoevaporative models correctly predict the observed
trend of inner-disc lifetime as a function of stellar mass with an increased
steepness for stars smaller than 0.3 Solar mass, indicating that X-ray
photoevaporation is a good candidate to explain the observed disc dispersal
process.
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