Extended Data Fig. 2: Fit of ZTF J1813+4251’s optical spectrum.
From: A dense 0.1-solar-mass star in a 51-minute-orbital-period eclipsing binary
a, A best-fit spectral model consisting of a low-mass main-sequence model and a hydrogen-rich white dwarf model to the observed spectrum of ZTF J1813+4251. The model, shown in red, has been convolved with the resolution of the spectrograph and rotationally broadened, and fit to the spectrum co-added in the rest frame of the donor, shown in black. b, A model spectrum fixed to the parameters derived from the SED analysis. We consider this model more reliable because it takes into account the Swift ultraviolet flux measurement, which strongly constrains the temperature of the white dwarf. The model, shown in blue, slightly underfits the blue part of the spectrum, plotted in black, which may be due to the presence of an accretion disk, or simply a systematic error introduced in the data reduction.
