About This Article
In this STAN, the STIS Team presents Cycle 32 updates to documentation and news to STIS users submitting Phase I proposals, as well as updates regarding stis_cti and time dependent sensitivity.
Cycle 32 Documentation and Phase I Reminders
Information on STIS in preparation of Cycle 32 proposals has been released in the HST Call for Proposals and Primer, and the STIS Instrument Handbook has been updated to reflect the current status of the instrument. PIs are encouraged to review Chapter 10.1 in the STIS Instrument Handbook (IHB) for a summary and checklist for HST Phase I proposals.
Special requirements (e.g. ORIENT, scheduling or timing constraints, ToOs, CCD and MAMA observations in one visit, and HST visits that exceed 30 buffer dumps carrying TIME-TAG data) must be justified quantitatively in the Phase I proposal. Proposals to use STIS's FUV- or NUV-MAMA detectors must also demonstrate that the proposed observations do not violate the bright object restrictions. A comprehensive summary, including a table on count rate limits, for drafting a suitable observing plan under these conditions are detailed in Section 7.7.
Special uses of STIS, including recommendations for users interested in coronagraphic observations, can be found in Chapter 12 of the IHB. We encourage PIs to utilize the STIS Coronagraphic Visualization Tool available on the Data Analysis and Software Tools webpage to aid their proposal planning. For coronagraphic observations requiring multiple ORIENTs, PIs are reminded that HST has a limited roll angle at any given time. Observations with large ORIENT differences will be scheduled at different times. Observers can view the "Roll Ranges Report" in the Visit Planner tool in APT to see the available ORIENT ranges when their object is schedulable.
STIS users preparing a program for Cycle 32 may refer to the Proposal Planning Toolbox, which includes deadlines, further documentation, and tools for submission. For additional inquiries, please contact the HST Help Desk.
Updated stis_cti v1.5.2: Bug Fix for Silent Failure during Multiprocessing
Earlier this year, the STIS team was alerted to a new bug that could affect users running stis_cti with multiple processors in parallel, which could cause stis_cti to silently fail to correct data. The bug was due to a combination of Numpy API changes for Numpy versions ≥ 1.24 and the inability of stis_cti to propagate errors raised by subprocesses. The subprocesses would create the expected CTI-corrected files from the uncorrected input files but fail before CTI corrections were made. Both issues have been fixed in the newly released version 1.5 of stis_cti. Users can upgrade their current version by running: pip install --upgrade stis_cti
Update on Time Dependent Sensitivity
The STIS team has observed a drop in the time dependent sensitivity (TDS) between 1800 and 2100 Å. The drop occurs in all modes that cover those wavelengths in both the NUV-MAMA and CCD, but the focus of our analysis is on G230L and G230LB. We have correlated the changing TDS with an increase in solar activity expected from the 11-year Solar Cycle. At the extremes, the sensitivity drops to ~5% below the currently adopted TDS corrections (Figure 1). We created a special monitoring program (PID: 17584) to better track the trending decrease, and we will update the TDSTAB reference files for the NUV-MAMA and CCD, and ETC values accordingly. Updated reference files are being created for the upcoming ETC release in early June, 2024, using the latest available data, shown in Figure 2. However, the decreasing TDS trend is not fully characterized, and may decrease in sensitivity more or less rapidly throughout the next year. For the NUV-MAMA in particular, the updated TDS files will adopt a conservative projection of no additional sensitivity drop because the two most recent TDS observations suggest the decrease could plausibly be leveling off, and overestimating the sensitivity decline could result in underestimating count rates for bright object safety screening. Users should therefore be warned that ETC calculations at wavelengths between 1800 and 2100 Å may not be accurately corrected for dates extrapolated into the next year. Calculations will likely be within the promised 10% accuracy for the ETC, but users who have questions or concerns about predicted signal to noise or bright object safety for observations in these wavelength ranges are encouraged to reach out to the HST Help Desk.
