Arcus Exposure Time Calculator ETC

1. Select a Grating:

Grating:	Wavelength Range
G110M:	( 1000-1280Å )

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.

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

	Point Source
	Extended Source (not implemented)
	Diameter is arcsec

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 (NOT IMPLEMENTED)
	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:
	a Black-body with temperature T =
	a Power-law: Fλ = λ **
	a Flat continuum in
	No continuum. If selected, the reference wavelength from part 2 above must correspond to one of the lines; and no extinction, redshift, or renormalization may be applied.

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

Do not Renormalize Point Source Spectrum. Use only for User Input Spectrum or Calibration Spectra.

5. Specify the expected background levels :

a)	Specify normalization for zodiacal background
	Standard zodiacal light normalizations:
b)	Specify normalization for earth shine background
	Standard earth shine light normalizations:
c)	Air Glow

Note that this form was based on one from the Hubble ETC site. The help links point to that site, however this is an Arcus form and therefore any queries should be directed to us at afoster@cfa.harvard.edu. Please don't bother the nice Hubble people!