Q.: How do I convert a line strength into a flux in Jy?

A.: If you have a total line flux in W/m2 you can convert it into an equivalent continuum flux in Jy for one of the NICMOS filters by dividing it by the filter bandwidth in Hz and then multiplying by 1.0E+26. This will give you a flux that you can use in the Exposure Time Calculator as though it were a continuum source. If you have a ground-based spectrum calibrated in Jy, you should integrate the spectrum across the filter bandwidth in order to determine the total flux, and then convert back to an equivalent continuum flux as above. If your source is entirely dominated by very strong line emission inside the filter bandpass, you can use the `emission line source' option in the Exposure Time Calculator, and enter the relevant line flux.