Binary microlensing with plasma environment -- Star and planet

TL;DR

This paper investigates how plasma environments around stars influence binary microlensing events, revealing that plasma causes additional caustics and alters magnification patterns, which can help study stellar winds.

Contribution

It introduces the effect of stellar plasma on binary microlensing, showing how plasma modifies caustic structures and magnification curves, a novel aspect in microlensing modeling.

Findings

Plasma causes extra caustics in microlensing.

Plasma shrinks star-generated central caustics.

Plasma pushes planetary caustics outward.

Abstract

Galactic microlensing has been widely used to study the star and planet. 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 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 which depends 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 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.