Release Notes for ETC 29.1.1

New Features

Welcome to ETC 29.1.1, released in January 2021.

Version 29.1 of the ETC (released November 2020) contains instrument updates and corrections to HST standard sources and background.

Version 29.1.1 fixes a bug encountered when recalling previous COS spectroscopic calculations.


  • The ETC evaluation date has been updated to 2022-Apr-01 (MJD 59670)
  • Updates to many CALSPEC model versions, listed spectral types, and V mag (HETC-265)
  • The zodiacal light scaling table was updated to fix some transcription errors. The locations of corrected values have been marked with an asterisk; neighboring regions will have been affected by interpolation. Users concerned about background-dominated calculations should recalculate their results. (HETC-317)
  • Fixed typos in metallicity for Non-Stellar Objects SSP 25 and SSP 5.


  • ACS throughputs were updated (HETC-268)
  • Updates to standard star spectra in CALSPEC and new monitoring data for WFC and SBC led to reductions of 1-2% in the throughputs of all three ACS channels.
  • ACS/WFC dark rate was increased from 0.0132 to 0.0137 e-/s/pix; the ACS/SBC dark rate was increased from 8.11e-6 to 8.28e-6 counts/s/pix (HETC-268)
  • ACS/WFC read noise for gain=2 was updated from 4.55 to 4.45 e- (HETC-268)


  • COS throughputs for blue modes G130M c1055 and c1096 have been increased by up to about 40% on FUVA to reflect the results of re-calibration of these modes and the corresponding updates to the FLUXTAB, TDSTAB, and DISPTAB reference files (HETC-269, RFD-644)
  • The short-wavelength edge of the G130M/c1055 wavelength range was moved from 901 \AA to 924 \AA to reflect the updated throughput (HETC-269, RFD-644)
  • COS detector dark rates have changed slightly (HETC-269)
  • COS/FUV buffer times are now reported independently per detector segment (HETC-316)
  • Fixed resel size reported on results page (HETC-224)


  • STIS throughputs for the CCD modes updated the underlying TDS; MAMA modes updated just the default MJD (HETC-270, RFD-646)
  • STIS CCD dark rates increased slightly from [0.022, 0.027, 0.032] to [0.023, 0.028, 0.033] cts/s/pix for [low, medium, high] settings, respectively (HETC-270)


  • WFC3 throughputs remain unchanged (HETC-271)
  • WFC3/UVIS dark rates increased from [0.0023, 0.0022] to [0.00276, 0.00271] e-/s/pix for the [UVIS1, UVIS2] chips, respectively (HETC-271)
  • CTE warnings triggered by low WFC3/UVIS background threshold now trigger at 20 e-/pix; instead of 12 e-/pix; (HETC-313)
  • WFC3/IR warning for minimum exposure time updated (HETC-306)


  • Added list of CALSPEC HST Standard Star Spectra files in use by the current ETC release to the User’s Guide

Under the Hood

  • Pysynphot remains at 0.9.14, which includes Vega normalization with the v008 CALSPEC model

Resolved Issues


  • The date for zodiacal light specification may now be specified out to 2025.


  • 29.1.1 fixes a bug that prevented the recall of previous COS spectroscopic calculations.
  • 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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