Exciting Updates to the James Webb Space Telescope's MIRI MRS Calibration!

In a groundbreaking development for astronomers and space enthusiasts alike, the MIRI (Mid-Infrared Instrument) team has officially released an update to the photometric calibration reference files for the Medium Resolution Spectrometer (MRS) of the James Webb Space Telescope (JWST). This significant upgrade, effective from CRDS context version 1263, is based on a more comprehensive analysis of various photometric calibrator stars that were observed during the JWST's first two operational cycles.

Previously, the calibration process for wavelengths below 18 microns heavily relied on a single O9V star, 10 Lac. However, the newly revised approach utilizes a broader averaging method, incorporating an impressive 10 different standard stars spanning O, A, and G spectral types. This change fundamentally enhances the calibration accuracy across the board.

What Does This Mean for Your Observations?

Astronomers can expect a noticeable impact from this update, with all calibrations becoming brighter by approximately 2% in short wavelengths and 5% in longer wavelengths. Even more impressively, this update has improved the consistency between MRS and MIRI Imaging modes to within 1% for the wavelength range of 4.9 to 18 microns. This alignment is crucial for anyone relying on precise photometric measurements to analyze cosmic phenomena.

However, the news isn't all sunshine and starlight for longer wavelengths (MRS Channel 4). Unfortunately, the new calibrator stars don’t provide a sufficient signal-to-noise ratio for a trustworthy photometric calibration beyond 18 microns. For these cases, the calibration will continue to rely on an infrared-bright asteroid and a young stellar object, specifically at the transitional boundary of Channels 3 and 4.

For those eagerly seeking even more detailed insights into these changes, a comprehensive document from Law et al. (2024) outlines the new calibration methodology and adjustments involved.

Get Involved!

Users of the JWST are encouraged to reach out to the MIRI team through the JWST Help Desk with any questions or concerns about these significant updates. These enhancements not only refine the capabilities of JWST but also underscore the ongoing evolution of our understanding of the universe.

Stay tuned for more updates as we explore the cosmos one photometric calibration at a time!