{ "cells": [ { "attachments": {}, "cell_type": "markdown", "id": "33ec5430-bede-4df7-9b24-a04a2865b52a", "metadata": {}, "source": [ "# JWST Modeling WFE Oscillations from IEC heaters\n", "\n", "On short timescales (a few minutes) the dominant source of WFE variations in JWST has been found to be a semi-periodic oscillation in astigmatism, which is now understood to be driven by heater resistors in the Instrument Electronics Compartment (IEC). This behavior was first identified in preflight testing at NASA's Johnson Space Center, and further characterized in flight. See [Telfer et al. 2024](https://www.spiedigitallibrary.org/conference-proceedings-of-spie/13092/3020273/Empirical-characterization-of-JWST-wavefront-error-variations/10.1117/12.3020273.short) for measurements and analyses. Briefly, thermostats cycle on and off periodically to keep the instrument control electronics boards in their operating temperatures, and differential thermal expansion and contraction exert tiny forces on the back of the OTE, enough to slightly affect its shape. \n", "\n", "This effect is small (typically 1-2 nm rms of astigmatism), and since the characteristic timescale is ~3 minutes, the time-averaged effect becomes even smaller in longer-duration observations. For the majority of datasets the impact of this effect on PSFs is negligible. However, some especially sensitive observations, such as transiting time series observations and coronagraphy, may under some circumstances be measurably affected by the IEC oscillations. \n", "\n", "STPSF therefore can retrieve the relevant IEC board temperatures from MAST, and use those to produce a model for amplitude and variation of this effect over time. This can be used to generate suitable time-variable PSFs, or alternatively the temperature telemetry itself may be used as ancillary data for de-correlating science observations. \n", "\n", "This notebook demonstrates how to retrieve IEC temperature measurements and IEC WFE models and use them in PSF calculations. \n", "\n", "