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