Special Calibrations
- It should be remembered that not all modes and uses of science instruments are routinely calibrated by STScI. When proposing, it should be determined whether observations of the nature being proposed are routinely calibrated by STScI.
- In addition to unusual modes, etc., some highly demanding observations may require such things as contemporaneous PSF observations with specific placement on the detector at the same position as the science target.
- If such demanding observations or other unusual modes which are not routinely calibrated by STScI are being proposed, it is the proposer’s responsibility to investigate whether special calibrations will be needed and to propose for additional time/orbits needed to make any necessary special calibration observations.
- If these are not included in the Phase I estimate, the proposal may be judged infeasible, or if somehow approved without the necessary calibrations, it may then exceed its TAC allocation when the necessary calibration observations are included and therefore require application to the TTRB for the extra needed time.
- Since it was the proposer’s responsibility to highlight and request this time in Phase I, it may potentially not be granted by the TTRB, or the necessary time may have to come out of the science allocation to the detriment of the science observations or sample size, etc. See more details about this in the usual relevant Phase I documents.
- Regarding PSF calibrations, some work has been done on providing PSFs for ACS, but it is the proposer’s/observer’s duty to determine if these will be sufficient for their science needs or if extra time for contemporary or more extensive observed PSFs may need to be included in a proposal’s required orbit estimate for the necessary calibrations. In particular, see Bellini et al. 2018 (ACS ISR 2018-08), Hoffman and Anderson 2017 (ACS ISR 2017-08), as well as Anderson and King 2006 (ACS ISR 2006-01) and references within those ISRs for much of the more recent work on PSFs.
- If the ACS/WFC postflash is actually needed to combat low-background CTE effects (though its use is often not recommended except in cases merely of pure detection and NOT for comparative photometry), the time required for using it to the recommended background level (now 30 electrons for Cycle 32 and going forward) must be factored in to Phase I orbital requests in order to ensure a sufficient orbital allocation.
- As of Cycle 31 and going forward, a new capability, Imaging Spectropolarimetry, has been enabled. For more information, if proposing to do Imaging Spectropolarimetry, or if you have been approved by the TAC to do it, please see item 1 in the April 2023 ACS STAN at https://www.stsci.edu/contents/news/acs-stans/acs-stan-april-2023, plus the bullet on ACS Spectropolarimetry under the "Instrumentation" section of the Cycle 32 Call for Proposals and the related items in the Instrument Handbook Section 6.1 and Instrument Handbook Section 6.3.1 as well as the more detailed text under "Imaging Spectropolarimetry" in the Cycle 32 HST Primer on the "Additional Observing Modes" page at HST Primer: Additional Observing Modes. Since calibration work has also been ongoing, please also read the newly-published March 2024 "Research Note" RNAAS article on the preliminary calibration of this mode, and the other material above, and please send a request to the HST Help Desk at https://stsci.service-now.com/hst so that knowledgeable ACS Group staff can advise you in greater and more current detail as to the latest calibration status and other specialized advice, etc.