Comparison between flare spectrum (blue) of GJ 436 against its quiescent spectrum (orange) near the Si III (left panel) and C II (right panel) emission lines. These spectra are computed by combining several HST-COS exposures. Absolute velocities are in the stellar rest frame but may be affected by biases resulting from the instrument and post-processing; however, the relative Doppler shift between the flare and quiescent spectra is physical.