Data Reduction Frequently Asked Questions

My extracted 1-dimensional NIR spectra show many spikes although the raw signal looks very good. What happened?


For data observed with very good seeing, steep slopes in the spatial profile of the spectra result in many spurious cosmic ray detections. This happens most often for NIR data, because they have a coarser spatial sampling (0.21 arcsec/pixel vs. 0.16 arcsec for UVB/VIS data), but due to their longer wavelengths better seeing than the bluer wavelength ranges.

The spurious cosmics may in turn cause spikes as can be seen in the plot (black spectrum). If you process the data with decode-bp = decode-bp - 32 (effectively treating the cosmic ray detections as good pixels) the spikes caused by spurious comics should vanish (red spectrum).