Background

Xavier Prochaska and Brad Holden of UCO/Lick have released a new web-based exposure time calculator for DEIMOS. Given the observer's desired grating parameters, slit width, CCD binning, and exposure parameters, the tool will plot the resulting S/N in the extracted spectrum as a function of wavelength. The user can select whether to plot the counts (DN) instead of S/N if desired, and can view the resulting data in tabular or graphical form.

Screenshot

Interpreting the output

It is important to note that the output S/N is per pixel. The S/N per resolution element will be higher depending on the number of pixels per resolution element.

The plot of noise versus wavelength offers a valuable planning tool. Knowing whether one is dominated by read noise, sky or object photon noise will affect your decision on binning, and observing strategy.

Caveats

This signal-to-noise estimator is applicable only to cross-dispersed echellette-mode spectroscopy, not to the low-dispersion mode of the ESI (nor to imaging).
Input magnitudes are on the AB system, not the Johnson system.
Output S/N is per pixel, not per resolution element.

Background

Screenshot

Interpreting the output

Caveats

See Also