J/AJ/169/6 JWST/MIRI photometry from flux calibration (Gordon+, 2025)
The James Webb Space Telescope absolute flux calibration. II. Mid-infrared
instrument imaging and coronagraphy.
Gordon K.D., Sloan G.C., Garcia Marin M., Libralato M., Rieke G.,
Aguilar J.A., Bohlin R., Cracraft M., Decleir M., Gaspar A., Kendrew S.,
Law D.R., Noriega-Crespo A., Regan M.
<Astron. J., 169, 6 (2025)>
=2025AJ....169....6G 2025AJ....169....6G
ADC_Keywords: Photometry; Infrared
Keywords: Calibration ; Flux calibration
Abstract:
The absolute flux calibration of the Mid-Infrared Instrument imaging
and coronagraphy is based on observations of multiple stars taken
during the first 2.5yr of James Webb Space Telescope operations. The
observations were designed to ensure that the flux calibration is
valid for a range of flux densities, different subarrays, and
different types of stars. The flux calibration was measured by
combining observed aperture photometry corrected to infinite aperture
with predictions based on previous observations and models of stellar
atmospheres. A subset of these observations was combined with model
point-spread functions to measure the corrections to infinite
aperture. Variations in the calibration factor with time, flux
density, background level, type of star, subarray, integration time,
rate, and well depth were investigated, and the only significant
variations were with time and subarray. Observations of the same star
taken approximately every month revealed a modest time-dependent
response loss seen mainly at the longest wavelengths. This loss is
well characterized by a decaying exponential with a time constant of
∼200 days. After correcting for the response loss, the band-dependent
scatter around the corrected average (i.e., repeatability) was found
to range from 0.1% to 1.2%. Signals in observations taken with
different subarrays can be lower by up to 3.4% compared to FULL frame.
After correcting for the time and subarray dependencies, the scatter
in the calibration factors measured for individual stars ranges from
1% to 4% depending on the band. The formal uncertainties on the flux
calibration averaged for all observations are 0.3%-1.0%, with
longer-wavelength bands generally having larger uncertainties.
Description:
The main James Webb Space Telescope (JWST) observations used for this
work are those taken specifically for the absolute flux calibration in
Cycles 1 and 2 (PIDs 1523, 1524, 1536, 1537, 1538, 1539, 4488, 4496,
4497, 4498, 4499, and 4578), which took place between 2022 July 10 and
2023 July 2, and 2023 July 3 and 2024 June 30 respectively. A small
amount of data taken in Cycle 3 (2024 July 1 - 2025 June 29) that was
available at the time of this work are included (PID 6607). These data
were supplemented with observations taken during Commissioning (2022
January - 2022 July) that provide the preliminary absolute flux
calibration (PIDs 1027 and 1045).
All of the targets were from the overall JWST absolute
flux-calibration program and are highly vetted hot stars, A dwarfs,
and solar analog stars. The exposure times were chosen to obtain data
with signal-to-noise ratios (S/Ns) of 200 or better.
The Mid-Infrared Instrument (MIRI) was used for the observations with
the filters: F560W (5.567um), F770W (7.475um), F1000W (9.849um),
F1130W (11.29um), F1280W (12.66um), F1500W (14.87um), F1800W
(17.83um), F2100W (20.47um), and F2550W (25.07um).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 183 368 James Webb Space Telescope Mid-Infrared Instrument
photometry
stars.dat 36 29 List of observed stars and their types (Table added
by CDS)
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See also:
J/PASP/119/994 : MIPS 24um calibrators (Engelbracht+, 2007)
J/AJ/149/11 : Spectra of candidate standard stars in mid-IR (Sloan+, 2015)
J/AJ/161/177 : Spitzer IRAC phot. of 36 JWST calibration stars (Krick+, 2021)
J/AJ/163/45 : IR absolute calibration. I. Calibration stars (Rieke+, 2022)
J/AJ/167/213 : Absolute Calib. IV. Templates for bright stars (Rieke+, 2024)
J/ApJ/841/15 : Synthetic JWST/MIRI fluxes and magnitudes (Jones+, 2017)
J/A+A/699/A97 : Limb-darkening coefficients for JWST (Claret+, 2025)
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- Name Source identifier
25- 28 I4 --- PID [1027/6607] Program identifier (1)
30- 41 A12 --- Type Source type (2)
43- 48 A6 --- Filter Filter identifier (3)
50- 58 A9 --- SubArray Subarray identifier (4)
60- 68 F9.3 d MDJ [59724/60532] Modified Julian Date of the
observation
70- 81 F12.6 s-1 PixRate [48.3/95011] Central-pixel rate (in DN/s)
83- 93 F11.4 --- Depth [1097/150762] Central-pixel well depth
(in DN)
95- 103 F9.5 s Time [0.42/239] Integration time
105- 117 F13.5 s-1 iFlux [252.2/2136812] Instrumental flux (in DN/s)
119- 130 F12.7 s-1 e_iFlux [0.97/5071] Uncertainty in iFlux (in DN/s)
132- 143 F12.7 s-1 ibkg [2.52/1122] Instrumental average background
per pixel (in DN/s)
145- 157 F13.9 mJy Flux [0.032/602.4] Instrumental flux in physical
units
159- 171 F13.11 mJy e_Flux [1e-4/0.84] Uncertainty in Flux
173- 183 F11.7 MJy/sr bkg [1.13/962.5] Instrumental average background
per pixel in physical units
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Note (1): The main James Webb Space Telescope (JWST) Mid-Infrared Instrument
(MIRI) observations used for this work include those taken specifically for
the absolute flux calibration in Cycles 1 and 2 (PIDs 1523, 1524, 1536, 1537,
1538, 1539, 4488, 4496, 4497, 4498, 4499, and 4578), some with a small amount
of data taken in Cycle 3 (PID 6607), and those taken during Commissioning
that provide the preliminary absolute flux calibration (PIDs 1027 and 1045).
Note (2): Observation occurrences of source types as follows:
ADwarfs = A-type dwarfs; 255 occurrences
HotStars = 40 occurrences
SolarAnalogs = 73 occurrences
Note (3): JWST Mid-Infrared Instrument (MIRI) filters as follows:
F560W = 5.567 um (36 occurrences)
F770W = 7.475 um (51 occurrences)
F1000W = 9.849 um (42 occurrences)
F1130W = 11.29 um (38 occurrences)
F1280W = 12.66 um (46 occurrences)
F1500W = 14.87 um (46 occurrences)
F1800W = 17.83 um (40 occurrences)
F2100W = 20.47 um (35 occurrences)
F2550W = 25.07 um (34 occurrences)
Note (4): JWST Mid-Infrared Instrument (MIRI) subarrays as follows:
FULL = 1024 x 1032 pixel2 (63 occurrences)
BRIGHTSKY = 512 x 512 pixel2 (40 occurrences)
SUB256 = 256 x 256 pixel2 (149 occurrences)
SUB128 = 128 x 136 pixel2 (11 occurrences)
SUB64 = 64 x 72 pixel2 (105 occurrences)
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Byte-by-byte Description of file: stars.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 23 A23 --- Name Source identifier
25- 36 A12 --- Type Source type (1)
--------------------------------------------------------------------------------
Note (1): Source types occurrences as follows:
ADwarfs = A-type dwarfs; 11 occurrences
HotStars = 8 occurrences
SolarAnalogs = 10 occurrences
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 22-Sep-2025