Normalizing the Source Flux

Regardless of whether you use your own input spectrum, a standard spectrum, or a modeled spectrum, you may wish to renormalize the source’s brightness. Sources can be normalized either to a specified flux or magnitude within a given band or to a specified flux density (erg~\cdot~cm^{-2}~\cdot~s^{-1}~\cdot~\AA^{-1}; Janskys (Jy) =10^{-23}erg~\cdot~cm^{-2}~\cdot~s^{-1}~\cdot~Hz^{-1}; AB magnitudes =8.9-2.5\log{F_{Jy}}) value at a given wavelength. When normalizing to flux at a given wavelength, it is necessary to choose a wavelength for which the source flux is non-zero, but it is not necessary to choose a wavelength within the pass band of the instrument’s observation mode.

Normalization is applied after redshift and extinction, but before emission lines are added.

Total flux, Vega magnitudes, AB magnitudes, or Janskys are used for point sources. Flux, Vega magnitudes, AB magnitudes, or Janskys per square arc second are used for extended/diffuse sources, and the brightness is considered to be uniform. For instruments that have global count rate limits (MAMA detectors, for example), the radius of the source in arc seconds should be specified. This allows the ETC to estimate the global count rate and to properly check the global count rate limit.

When using a user supplied or HST calibrated spectrum, it is not necessary to renormalize. Select the Do not renormalize option on the form, in which case the input file will be assumed to have the correct units (erg \cdot cm^{-2} \cdot s^{-1} \cdot \AA^{-1}) for point sources and [erg \cdot cm^{-2} \cdot sec^{-1} \cdot \AA^{-1} \cdot arcsec^{-2}] for diffuse sources.

The bands supported by the ETC can be found below:

  • Johnson: U, B, V, R, I, J, K
  • Bessell: H, J, K
  • Cousins: R, I
  • Sloan: U, G, R, I, Z
  • NICMOS: F110W, F160W
  • ACS: F435W, F475W, F555W, F606W, F625W, F775W, F814W, F850LP
  • WFC3/UVIS: F218W, F200LP, F225W, F275W, F300X, F336W, F350LP, F390W, F438W, F475X, F600LP
  • WFC3/IR: F098M, F105W, F110W, F125W, F140W, F160W
  • HST: Filter selected for observations


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