STIS Spectroscopic ETC

This form will calculate the count rates and S/N ratio for a simulated spectrum of ONE source in a STIS spectroscopic 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 one Grating/Prism and an associated Slit/Filter:

1st Order CCD
Grating: Cen. Wave.
( 5240 - 11490 )
( 2900 - 5700 )
( 1685 - 3065 )
Slit ------------
1st Order FUV MAMA (see special MAMA countrate restrictions)
Grating: Central Wavelength
( 1150 - 1736 )
Slit ------------
1st Order NUV MAMA (see special MAMA countrate restrictions)
Grating Cen. Wave.
( 1570 - 3180 )
Slit ------------
MAMA Echelle
NUV FUV
Grating Cen. Wave. Slit Grating Cen. Wave. Slit

MAMA Objective Prism
( 1150 - 3000 )
Filter ----------

Specify additional CCD parameters:

Binning Gain # Frames
Dispersion Axis Spatial Axis

2. Specify the exposure parameters:

Signal-to-noise ratio is calculated per spectral resolution element.

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

S/N or exposure time specified for a wavelength of Å.
Currently selected disperser: not displayed with pass band

Select the source type. The indicated extraction region (centered on the target) that will be used for the S/N ratio calculation:

pixels.

The extraction region is two native pixels wide in the dispersion direction.

The width of a resolution element is two native pixels wide along the dispersion direction, and the signal-to-noise is calculated for a 2 native pixel resel, regardless of the binning used.

The extraction region is two native pixels wide in the dispersion direction and one (binned) pixel in the spatial direction.

The width of a resolution element is two native pixels wide along the dispersion direction, and the signal-to-noise is calculated for a 2 native pixel resel, regardless of the binning used.

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:
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:

= (Vega magnitudes) (arcsec-2 for extended sources)
= (AB magnitudes) (arcsec-2 for extended sources)
Normalize target using bandpass of filter selected above to AB Mag
ergs cm-2 s-1 Å-1 (arcsec-2 for extended sources) at Å.

5. Specify the expected background levels :

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