April 2023 STAN

In this STAN, the STIS Team presents Cycle 31 updates to documentation and news to STIS users submitting Phase I proposals, including updates to the FUV-MAMA dark rate adopted for ETC v31.1. Additionally, we recapitulate STIS' posters and presentations at the 241st AAS Winter conference that may also assist users submitting a proposal.

Cycle 31 Documentation and Phase I Reminders

Information on STIS in preparation of Cycle 31 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 schedule 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 31 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. 

ETC v31.1 Updates

The STIS team has revised the FUV-MAMA dark rate values for the ETC v31.1. To provide better estimates for users that may be most impacted by the varying dark rates, the adopted values recommended for the first two orbits are 3.0 × 10⁻⁵counts/pix/s, revised from 5.0 × 10⁻⁵ counts/pix/s in the center of the glow region, with a description of NONE. The value recommended for the third orbit in the detector is 7.5 × 10⁻⁵ counts/pix/s, revised from 1.5 × 10⁻⁴ counts/pix/s, with a description of LOW glow. At the D1 psuedo-aperture position after the detector has been on longer (MEDIUM) has been revised from to 2.0 × 10⁻⁴ counts/pix/s to 1.5 × 10⁻⁴ counts/pix/s, while the default ETC selection for this parameter will remain at LOW.

The ambient instrument environment is running ~1°C warmer compared to the past few years (possibly due to NICMOS now running as a minor frame "sniffer").  However, the FUV detector dark rate remains dominated by detector-time-on rather than the OM1CAT temperature, indicating the ambient environment is not the primary cause of the dark and glow.

Updates to the CCD dark current for ETC v31.1 are indicated on the figure below. The STIS CCD dark rate was extrapolated at the top, middle, and bottom of the detector. The trends are derived from temperature-corrected darks and the "low" value at the top of the detector was adjusted upward by 1σ of the temperature correction distribution to give a conservative value for the detector's lowest dark rate region (near the read-out amplifier and E1 position).

The NUV dark rates and the CCD read noise parameters remain unchanged from Cycle 30. The full list of instrument performance monitors are available and updated on under the STIS Performance webpage. 

The ETC documentation has been updated to better describe the input parameters for the users and the team is refining the recommendations for these settings. The latest version of the ETC is strongly recommended to PIs submitting proposals for determining accurate exposure times and checking for compliance with bright object restrictions.

STIS at the 241st AAS Meeting

Posters, presentations, and science results with STIS are available on the iPoster sessions webpage maintained by the American Astronomical Society. 

• STIS team iPosters:

Update on the Absolute Flux Recalibration of the HST/STIS Modes – Joleen Carlberg

Performance Updates for the Space Telescope Imaging Spectrograph – Sophia Medallon

On behalf of the STIS team, Keyi Ding announced and performed a demo on a new set of introductory Jupyter Notebooks available on the STIS-Notebooks Github Repository for users interested in viewing and analyzing various STIS data types.