Top: an intrinsic stellar spectrum which is Doppler shifted and then convolved. Middle: the convolved spectrum is down-sampled to SPIRou’s resolution, but no photon noise is added, thus representing a noiseless observation. Here, each black point represents a SPIRou pixel. This synthetic observation is then upsampled using spline interpolation as a precursor to constructing the template. Bottom: discrepancies between the upsampled and convolved spectrum, indicating that the template will contain altered stellar features.