Chapter 10:
Exposure-Time Calculator (ETC)
10.1 The COS Exposure Time Calculators
10.2 Count Rate, Sensitivity, and S/N
10.2.1 Centering accuracy and photometric precision
10.3 Detector and Sky Backgrounds
10.3.1 Detector dark background
10.3.2 Earthshine
10.3.3 Zodiacal light
10.3.4 Geocoronal airglow emission
10.4 Extinction Correction
10.5 Tabular Sky Backgrounds
10.6 Examples
10.6.1 A Flat-spectrum source
10.6.2 An early-type star
10.6.3 A solar-type star with an emission line
In this chapter we discuss the COS exposure time calculators, which are essential tools for planning your observations. We show the backgrounds which contribute to the spectrum or image, and discuss the various choices of levels available in the ETCs. We also discuss extinction, which can have a large effect on the observed flux from a target.
