STIS Target acquisition ETC

This form will calculate the count rates and S/N ratio for a simulated spectrum of ONE source in a STIS 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.

1. Select an ACQ Filter/Slit:

Specify the size of the Check-Box:

A check-box of 3 is used for point sources.

Check-box size for extended sources = Must be an odd number from 3 through 101 for extended sources.
SNR is calculated for SIZEAXIS1 = 32, SIZEAXIS2 = 32.

2. Specify the exposure parameters:

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

A S/N of at least 40 is recommended for the acquisition of a point source; see the STIS Instrument Handbook (chapter 8) for recommendations for extended sources and for peakups.

Select the source type.

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