COS Spectroscopy Target Acquisition ETC

This form will calculate the count rates and S/N ratio for a simulated bandpass of ONE source in a COS spectroscopic target acquisition 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.

The calculation may take a slightly longer time than in earlier versions of the ETC.

1. Select grating (mode) and aperture:

---------- FUV ---------- ---------- NUV ----------
Grating: Cen. Wave. Grating: Cen. Wave.
FUV selections above apply to: NUV mode:
ACQ/Search, PeakD and PeakXD.

For PeakXD only:
Select NUV stripe:

Aperture ----------

2. Specify the exposure parameters:

​Chapter 8 of the COS Instrument Handbook recommends a S/N of at least 40 for ACQ/Search and ACQ/PeakD. NUV ACQ/PeakXDs should achieve at least a S/N of 40 for the specified stripe. FUV ACQ/PeakXDs with NUM_POS > 1 (Cycle 25 or later) should achieve a S/N of at least 40 using both segments.

Exposure time needed to obtain a S/N ratio of
S/N ratio reached in an exposure time of seconds.

Select the source type:

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

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)
(vacuum)

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:
Bandpass 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