Skip to main content
June 5, 2023

In this STAN we announce a COS poster to be presented at the 242nd AAS meeting and inform users of the alpha release of a revised exposure time calculator for Hubble.

COS Poster at the 242nd Meeting of the American Astronomical Society

A COS poster will be presented at the AAS meeting. We invite all COS users to review it to find out about the latest developments for COS. Below we include a link to the poster. Additionally, all COS posters are archived on the COS poster page.

230.08 Updated Status and Performance of the Cosmic Origins Spectrograph (S. Gomez and the COS Team)

Entering its fifteenth year of operation, the Hubble Space Telescope’s (HST) Cosmic Origins Spectrograph (COS) has enabled major strides in our understanding of the universe with its proficiency in ultraviolet spectroscopy. The COS team presents the scientific community with a general status update for the instrument from recent COS calibrations. The COS Exposure Time Calculator (ETC) incorporates updated throughputs and dark rates for both the Near-Ultraviolet (NUV) and Far-Ultraviolet (FUV) detectors. The NUV detector’s dark rate has remained stable and the FUV detector’s dark rate has approximately doubled; these increases in dark rates are expected due to heightened solar activity and will be incorporated into ETC v31.2. Additionally, the COS calibration pipeline (CalCOS) will use an updated gain sag table to account for new gain sag holes across the FUV detector, as well as a new time-dependent sensitivity table with updated breakpoints and slope. Finally, the COS team recommends using two FP-POS when observing with the LP6 G160M grating, depending on the desired signal-to-noise ratio and number of orbits for an observation. These recommendations minimize the overhead that is caused by LP6’s inability to take concurrent wavelength calibration exposures.


Back to Top

Alpha Release of the Pandeia-based HST Exposure Time Calculator (ETC)

J. Ryon, S. Lockwood, & V. Laidler

STScI has released an alpha version of the Pandeia-based Exposure Time Calculator (ETC) for the Hubble Space Telescope (HST) at The alpha release is intended for users to familiarize themselves with the new interface and perform example calculations for supported observing modes.

IMPORTANT: The official HST ETC for Cycle 31 proposal submissions is located at Please do not include results from the Pandeia-based HST ETC in Cycle 31 programs.

Pandeia is a pixel-based exposure time calculator paired with a modern graphical user interface. While Pandeia was developed for JWST, it is a general framework, data-driven ETC capable of supporting multiple missions, including HST. It includes advanced features that go beyond the capabilities of previous ETCs, such as algorithms that accurately model both data acquisition and post-processing of data, and it provides functionality for users to efficiently explore and compare a large volume of parameter space in their calculations.

The HST implementation of Pandeia supports many HST observing modes. Its graphical user interface allows users to create workbooks to manage related sets of calculations, create complex astronomical scenes with multiple sources, compare the results of multiple calculations, and share their workbooks with other users. Several HST observing modes are not yet available, but will be made available in future releases. For COS, these include NUV spectroscopy, imaging, and imaging target acquisitions; additionally, buffer fill times and bright object warnings are not yet included in the results.

Migration Guide has been prepared to facilitate the transition to the Pandeia-based ETC for experienced users of the official ETC. Please start there if you are not already experienced with the JWST ETC.

We request feedback from the user community regarding the alpha release via the HST Help Desk, particularly feedback related to the clarity of calculation results. An ETC representative will also attend the summer AAS meeting in Albuquerque to demo the Pandeia-based ETC and answer questions.

User's Guide for the Pandeia-based HST ETC is available on HDox, and Known Issues are available as a Knowledge Base article on the HST Help Desk.


Back to Top



Please Contact the HST Help Desk with any Questions