Binary microlensing with plasma environment – star and planet

Abstract

ABSTRACT Galactic microlensing has been widely used to study stars and planets. The stellar wind plays an important role in the formation, environment, and habitability of the planet. In this work, we study a binary microlensing system including the stellar wind, i.e. a star with a plasma environment plus a planet. Plasma surrounding the main lens causes chromatic deflection of the light rays, in addition to the gravitational one. As a result, such a lensing system can generate complicated caustics that depend on the different lensing parameters. In this work, we study the magnification curves for different traces of the background source and compare the transitions of the formation of ‘hill and hole’ in the magnification curves. We find that the plasma will cause extra caustic, shrink the central caustics generated by the star, and push the caustic by the planet outwards. Observations and modelling of binary microlensing curves with taking plasma effect into account can provide a potential method to study the plasma environment of the stars. In case of a high plasma density of the stellar wind, the plasma lensing effects will be observable in the sub-mm band.