Region of the spectrum obtained of Lovejoy on UT 2015 May 11 that contains the forbidden oxygen line at 6300 Å. Note that the cometary line appears redward of 6300 Å  due to Doppler shifting caused by the comet’s geocentric velocity. The data are represented by a histogram (black) with 1σ errorbars. Due to the high signal-to-noise, the error bars are quite small, with typical values around 1% of the flux. The data are fitted with two separate Gaussians corresponding to the telluric (red) and cometary (blue) features. The sum of the two Gaussian components is plotted in green.