  The recurring transient outbursts in low-mass X-ray binaries (LMXBs) provide
us with strong test-beds for constraining the poorly understood accretion
process. While impossible to image directly, phase-resolved spectroscopy can
provide a powerful diagnostic to study their highly complex, time-dependent
accretion discs. We present an 8-month long multi-wavelength (UV, optical,
X-ray) monitoring campaign of the new candidate black hole LMXB MAXI
J0637$-$430 throughout its 2019/2020 outburst, using the {\em Neil Gehrels
Swift Observatory}, as well as three quasi-simultaneous epochs of Gemini/GMOS
optical spectroscopy. We find evidence for the existence of a correlation
between the X-ray irradiation heating the accretion disc and the evolution of
the He {\sc ii} 4686 \AA emission line profiles detected in the optical
spectra. Our results demonstrate a connection between the line emitting regions
and physical properties of the X-ray irradiation heating the discs during
outburst cycles of LMXBs. Further, we are able to show that changes in the
physical properties of the irradiation heating the disc in outburst can be
imprinted within the H/He emission line profiles themselves in these systems.
