Poster Abstract

P5.3 Michael Mueller (University of Leiden)

Theme: Delivering accessible and science-ready radio data

JWST-MIRI data-reduction pipeline: fringe correction in spectroscopic data

The 6.5m James Webb Space Telescope (JWST) is slated to be launched in March 2021. Its Mid-Infrared Instrument (MIRI) has R~3,000 spectroscopic capabilities using the Medium-Resolution Spectrometer (MRS). As is common for spectrometers of this resolving power, MRS is significantly affected by fringes, i.e., periodic gain modulations due to standing waves in the optical path.

We will present the fringe-correction method employed in the JWST data-reduction pipeline for MIRI-MRS data. It uses a two-step approach: data are divided by an appropriate model-derived fringe flat, followed by a subtraction of fitted sinusoidal residual fringes.

The fringe flat is derived from fitting an analytic model (for one or more resonator thicknesses) to laboratory observations of a spatially fully extended source. We will discuss the fitting procedure used to derive the fringe flats.
We find the resulting fringe flats to be very stable within any test campaign, however there are significant campaign-to-campaign differences. We attribute this to slight mechanical irreproducibilities associated with warming up and/or cooling the instrument. This suggests that the in-flight fringe pattern will be stable. Fringe flats derived from ground-test data will probably not be useful for science calibration, new fringe flats will have to be derived from in-flight observations.

Combining current fringe flats and residual fringe correction, MRS spectra of point sources and of spatially fully extended sources can be fringe-corrected within the requirements. Challenges remain for semi-extended sources, for which an imaging spectrometer like MRS is particularly well suited. We will discuss our plans for solving this issue.