NICER observation list: Target ID 468001

We propose to use the advanced energy and time resolutions of NICER to search for discrete spectral features during thermonuclear X-ray bursts from 4U 1820-30. During the strong bursts of this source, the photosphere of the neutron star can temporarily be lifted to large radii, ejecting nuclear burning ashes that can imprint the burst spectra. We aim, with the proposed observations, to double the number of bursts detected by NICER from this source. Stacking bursts together does significantly improve the detection of spectral lines, making it possible to track their energy through the burst evolution. By identifying lines related to heavy elements we can explain burst nucleosynthesis processes and probe the equation of state of the neutron star through the measured gravitational redshift.