COS Instrument Handbook for Cycle 24 |

help@stsci.edu |

Cosmic Origins SpectrographInstrument Handbook for Cycle 24 > Chapter 7: Exposure-Time Calculator (ETC) > 7.3 Sensitivity, Count Rate, and S/N

A complete theoretical discussion of the exposure time as a function of instrument sensitivity and signal-to-noise ratio is given in Chapter 6 of the STIS Instrument Handbook and will not be repeated here. However, COS has several characteristics that simplify signal-to-noise calculations.t = the integration time, in secondsNote that the detector dead-time effects discussed in Section 4.1.5 and Section 4.2.5 are not included in the ETC, which will over-predict the count rates and resulting S/N ratios for bright targets.

Cosmic Origins SpectrographInstrument Handbook for Cycle 24 > Chapter 7: Exposure-Time Calculator (ETC) > 7.3 Sensitivity, Count Rate, and S/N