Detecting the inner regions of discs around sources of microlensing with Roman Space Telescope

TL;DR

This study assesses the feasibility of detecting circumstellar disc inner regions via microlensing with the Roman Space Telescope, revealing distinctive light curve features and estimating detection probabilities for disc-induced signals.

Contribution

The paper introduces a simulation-based analysis of microlensing light curves to identify signatures of circumstellar discs around bulge stars using Roman Space Telescope data.

Findings

Disc crossing causes wide peaks and flattening in light curves.

Discs can break the symmetry of microlensing light curves.

Detection probability is approximately 3% for single and 20% for binary microlensing events.

Abstract

The inner region of circumstellar discs makes an extra near-infrared emission (NIR bump). Detecting and studying these NIR bumps from nearby stars have been done mostly through infrared interferometry. In this work, we study the feasibility of detecting NIR bumps for Galactic bulge stars through microlensing from observations by The Nancy Grace Roman Space Telescope (RST) survey. We first simulate microlensing light curves from source stars with discs in near-infrared. Four main conclusions can be extracted from the simulations. (i) If the lens is crossing the disc inner radius, two extra and wide peaks appear and the main peak of microlensing light curve is flattened. (ii) In microlensing events with the lens impact parameters larger than the disc inner radius, the disc can break the symmetry of light curves with respect to the time of closest approach. (iii) In caustic-crossing binary microlensing, the discs produce wide peaks right before entering and immediately after exiting from the caustic curves. (iv) The disc-induced perturbations are larger in the W149 filter than in the Z087 filter, unless the lens crosses the disc condensation radius. By performing a Monte Carlo simulation, the probabilities of detecting the disc perturbations by \wfirst~are estimated ~3 and 20 per cent in single and binary microlensing, respectively. We anticipate that RST detects around 109 disc-induced perturbations during its microlensing survey if 5 per cent of its source stars have discs.