ETC and pysynphot
The ETC relies heavily on the synthetic photometry packages pysynphot. This package simulates photometric data and spectra as they are observed by the HST instruments. For this, it relies on the information of the HST instruments throughput part of the Calibraton Data Base System (CDBS) at STScI. Pysynphot is intended as a modern-language successor to the IRAF/STSDAS SYNPHOT package, and is developed and maintained by the Science Software Branch (SSB) at STScI.
Except for the details of the SYNPHOT call descriptions and parameters, the ETC documentation describing SYNPHOT applies equally well to pysynphot.
The equation. The diagram below depicts the relationship between the ETC and pysynphot. The user first directs his/her web client to the ETC web server. The user then inputs instrument and exposure level parameters to the ETC input form that are then transmitted to the ETC application web server. The parameters are then packaged up as pysynphot request(s) and transmitted to the pysynphot software. The pysynphot response, which is a count rate in photons per second, is then retrieved by the ETC application and used in the final calculation and in the SNR/Exposure Time Report.
