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COS Imaging Target Acquisition ETC

This form will calculate the count rates and S/N ratio for a simulated bandpass of ONE source in a COS imaging target acquisition (i.e., ACQ/Image or ACQ/Search with a mirror) observation.

For general help on how to use this Exposure Time Calculator or for help on various topics, click on the appropriate highlighted words.
Please ensure that you have read the current release notes and recent news before submitting any ETC calculations.

1. Select mirror and aperture:

Mirror ------------

Aperture ----------

Select the acquisition mode:
The photometric extraction region is a 9 X 9 box for ACQ/IMAGE mode, or a 220 X 470 box for ACQ/SEARCH mode.

2. Specify the exposure parameters:

Select the source type:

The photometric extraction region is the same for both point and extended sources and varies from mode to mode.

Exposure time needed to obtain a S/N ratio of - Recommended S/N values: ACQ/IMAGE 20 for PSA, 30 for BOA; ACQ/SEARCH 40 (both apertures).
S/N ratio reached in an exposure time of seconds.

3. Choose one of the following spectral distributions for the source:

Please note: for User supplied and uploaded spectrum, please use only FITS or text (DAT) format files.
Upload Spectrum File:
Other HST Spectrum:
CDBS Synphot spectrum file
Castelli and Kurucz Models: [Sp Teff log(g) log(z)=0]
Pickles Models: (Sp Teff)
Kurucz Models:
Bruzual Synthetic Stellar Spectra:
HST Standard Star spectra:
Phoenix M dwarf Models:
Non-Stellar Objects:

Specify the extinction E(B-V) =

Extinction applied normalization.

Specify the redshift z =

Add emission lines to the input spectrum (optional): Note: emission lines are added *after* the spectrum has had extinction, renormalization, and redshift applied.

Line Center FWHM Integrated Flux
Å Å (erg/cm2/s)

Note: integrated flux units are per arcsec2 for extended sources. All three of the parameters (line center, fwhm and integrated flux) must be specified for an emission line to be included.

4. Normalize the target's flux:

(arcsec-2 for extended sources) at
(arcsec-2 for extended sources) in filter:
Filter selected above in Question 1 (for observations)
Typically select Vega magnitude above
Typically select AB magnitude above

5. Specify the expected background levels :

a) Specify normalization for zodiacal background
R.A.: (hh:mm:ss or decimal degrees)
Dec.: (dd:mm:ss or decimal degrees)
either degrees
- or -
b) Specify normalization for earth shine background
c) Air Glow