Characterization of the visit-to-visit Stability of the GR700XD Spectral Traces for NIRISS/SOSS Observations

TL;DR

This study analyzes the stability of spectral trace positions in NIRISS/SOSS observations, establishing a model to predict trace shifts based on the GR700XD pupil wheel position, enhancing wavelength calibration accuracy.

Contribution

We developed an analytic model linking pupil wheel position to spectral trace shifts, improving trace position prediction accuracy for NIRISS/SOSS data.

Findings

Trace position correlates one-to-one with pupil wheel position.

The model predicts trace shape with ~0.1 pixel accuracy.

Model aids in low SNR cases and time series tracking.

Abstract

In this report, we present the results of our analysis of trace position changes during NIRISS/SOSS observations. We examine the visit-to-visit impact of the GR700XD pupil wheel (PW) position alignment on trace positions for spectral orders 1 and 2 using the data obtained to date. Our goal is to improve the wavelength solution by correlating the trace positions on the detector with the PW position angle. We find that there is a one-to-one correspondence between PW position and spectral trace rotation for both orders. This allowed us in turn to find an analytic model that is able to predict a trace position/shape as a function of PW position with sub-pixel accuracy of about ~0.1 pixels. Such a function can be used to predict the trace position in low signal-to-noise ratio cases, and/or as a template to track trace position changes as function of time in Time Series Observations (TSOs).