Release Notes for ETC 27.2

New Features

Welcome to ETC 27.2. This version of the ETC implements the following improvements, notably:


  • Certain error messages have been clarified during source normalization (HETC-123)
  • Entering a negative value for desired SNR now correctly results in an error (HETC-119)
  • The drop-down menu description of some extinction curves has been clarified (HETC-161)
  • Links to the STScI website have been updated
  • The ETC evaluation date remains at 2020-Apr-01 (MJD 58940)


  • Throughput values for the SBC detector and filters were updated. A recent study has shown that the throughput values for ACS/SBC observations have been significantly underestimated. This means that calculations performed with the ETC prior to version 27.2 underestimated source signal. The underestimate is at a level of 30% for all filters other than F122M, for which the level is 20%. ETC version 27.2 includes corrections to the throughput values. Note that these corrections now cause calculations using the F122M filter to overestimate source signal by 10%. These corrections also cause an overestimate of all SBC prism calculations by about 30%. The MJD of the filter throughputs was updated to 2020-Apr-02. (HETC-144)
  • The language of a calculation time warning now clarifies that the time listed in the warning is a per-frame time. (HETC-122)


  • FUV detector dark values have been updated. (HETC-142)
  • The error message occurring when a MAMA detector is selected while CCD-related binning & gain parameters are modified has been clarified. (HETC-121)


  • Throughput values for the NUV and CCD detectors have been updated by a few percent based on updated time-dependent sensitivity projections. (HETC-134)


  • The UVIS dark values have been updated. (HETC-130)


  • The user’s guide has been updated with new dark values. (HETC-133)
  • Links to the STScI website will be updated as needed.

Under the Hood

  • The ETC has been ported to Python 3.X. This has resulted in some small performance degradation, most noticeably in COS spectroscopic and spectroscopic target acquisition calculations.
  • The ETC is using pysynphot 0.9.12, which is obtainable from the Astroconda channel, running under Python 3.X.

Resolved Issues


  • The ETC 26.1 underestimated the S/N obtained with the new G140L/800 mode, and conversely, overestimated the time required to achieve a certain S/N. This was subsequently corrected in ETC 26.2, and we strongly recommend that users recalculate their results using the most recent version of the ETC.

Known Issues

Please see the News and Known Issues page for known issues with this release.


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