James Webb Space Telescope Feed Post

Arxiv: The James Webb Space Telescope Absolute Flux Calibration. III. Mid-Infrared Instrument Medium Resolution IFU Spectrometer Published: 9/23/2024 9:01:40 PM Updated: 9/23/2024 9:01:40 PM

Paper abstract: We describe the spectrophotometric calibration of the Mid-InfraredInstrument's (MIRI) Medium Resolution Spectrometer (MRS) aboard the James WebbSpace Telescope (JWST). This calibration is complicated by a time-dependentevolution in the effective throughput of the MRS; this evolution is strongestat long wavelengths, approximately a factor of 2 at 25um over the first twoyears of the mission. We model and correct for this evolution through regularobservations of internal calibration lamps. Pixel flatfields are constructedfrom observations of the infrared-bright planetary nebula NGC 7027, andphotometric aperture corrections from a combination of theoretical models andobservations of bright standard stars. We tie the 5--18um flux calibration tohigh signal/noise (S/N; ~ 600-1000) observations of the O9 V star 10 Lacertae,scaled to the average calibration factor of nine other spectrophotometricstandards. We calibrate the 18--28um spectral range using a combination ofobservations of main belt asteroid 515 Athalia and the circumstellar diskaround young stellar object SAO 206462. The photometric repeatability is stableto better than 1% in the wavelength range 5--18um, and the S/N ratio of thedelivered spectra is consistent between bootstrapped measurements, pipelineestimates, and theoretical predictions. The MRS point-source calibration agreeswith that of the MIRI imager to within 1% from 7 to 21um and is approximately1% fainter than prior Spitzer observations, while the extended sourcecalibration agrees well with prior Cassini/CIRS and Voyager/IRIS observations.