Calibration

Lamps currently available in the WYFFOS calibration unit (and their position number) are:

Tungsten	1
Neon	2
Mercury	3
Helium	4

Sky subtraction with fibres is never as good as with a slit spectrograph, since one is limited by the fibre diameter. Achieving the best possible sky subtraction with fibres requires careful planning and observing strategies, and inevitably involves tradeoffs. For instance, one can assign a `sky' fibre next to each object fibre, which reduces the fibre multiplexing advantage by a factor of ~2. Another strategy is to `beam-switch' (move the telescope back and forth between objects and neighboring sky), but this of course reduces the integration time on source.

Absolute flux calibration can never be done with fibres, since again one is limited by the fixed fibre diameter.