Updated Sensitivities of the Five STIS L-mode Gratings

TL;DR

This paper recalibrates the sensitivities of the five low-resolution STIS gratings after updates to standard star models, ensuring more accurate historical data calibration within a 1-1.5% agreement range.

Contribution

It provides updated spectral sensitivities for the five STIS L-mode gratings based on revised standard star models, improving calibration accuracy.

Findings

Sensitivities agree within 1% across most wavelengths

Discrepancies up to 1.5% in hydrogen-absorbed regions

Updated calibration tables delivered to CRDS in 2022 and 2023

Abstract

Re-derivation of the sensitivities of all of the Space Telescope Imaging Spectrograph (STIS) observing modes were required after major updates were introduced to the model atmospheres of the three primary standard stars. The new predicted continuum fluxes were up to 2-3% different from the models used to originally calibrate STIS. This work focuses on the re-derivation of spectral sensitivities for the five STIS low-resolution (L-mode) gratings: G140L, G230L, G230LB, G430L, and G750L, which span wavelengths from the far-ultraviolet through the near infrared. Updated photometric throughput tables were delivered to the Calibration Reference Data System (CRDS) on April 7, 2022 and April 14, 2023, which triggered a recalibration of all historical STIS datasets taken with these modes. The sensitivities derived from each of the standard stars typically agree with one another to better than 1%, though discrepancies as large as 1.5% are found in spectral regions most impacted by hydrogen absorption.