Spectral fit for MARTA_4502, observed using grating G140M (left) and G235M (right). The black line represents the observed flux, the blue line the stellar continuum fit, and the red lines the emission-line Gaussian fits. In the bottom panels we show in grey the residuals from the fit, while the orange line represents the pipeline error estimates. The zoom-in panels at the top provide a more detailed view of specific spectral features: the auroral lines [S II] λ4068 and [O III] λ4363 (left) and the spectral range around the [O II] λλ7320,7330 auroral lines (right).