NICER observation list: Target ID 758001

We propose to exploit NICER's perfectly suited capabilities to unveil the physical mechanism driving the super-orbital variability in wind-fed supergiant X-ray binaries. Our science objectives require a monitoring of these systems along their different super-orbital phases to measure stable and periodic changes in the absorption column density, flux, and eventually slope of the continuum emission across a representative number (~12) of super-orbital cycles. 96 short NiCER observations (500 s each) spanning a total of 6 months (roughly 4 observations per week, 48 ks in total), will permit us to study the mechanism driving the super-orbital variability in a representative source of this class, 4U 1538-52.