Upgrade to Pro — share decks privately, control downloads, hide ads and more …

JWST Absolute Flux Calibration

Karl Gordon
August 11, 2022

JWST Absolute Flux Calibration

Presentation to the internal STScI Cross-Mission Calibration Working Group

Karl Gordon

August 11, 2022
Tweet

More Decks by Karl Gordon

Other Decks in Science

Transcript

  1. EXPANDING THE FRONTIERS OF SPACE ASTRONOMY JWST Absolute Flux Calibration

    Karl D. Gordon, Cross-Mission Calibration WG, 11 Aug 2022
  2. Basics Calibrate all JWST instruments – 0.6 to 28.3 microns

    – Inherit high-quality cross-calibration between instruments Requirement – 5% for imagers (coronagraphs 5-15%) – 10-15% for spectrographs – AbsFlux program contributes a portion of this requirement Goal: better than 5% (for all?) Test for systematics in calibrators – Different types needed (3 minimum) Cross-calibration with Hubble and Spitzer (& others) Clear and documented methodology (flux prediction & calfactor)
  3. Targets Stars – “Simple”, “straightforward” to model (stellar atmospheres) –

    Heritage (used by Hubble, Spitzer, ground-based) Hot stars (white dwarfs and OB stars) – Simple atmospheres (Hubble primary calibrators) A Dwarfs – Simple atmospheres (Spitzer primary calibrators) Solar Analogs – Solar analogs (Spitzer, strong heritage in IR community)
  4. Good calibrator characteristics • Single star • “Easy” to Model

    star • Previously used as a standard (if possible) • Not variable (< 0.25% 1-sigma) • Not a close binary • No stellar disks (gas or dust) • Low stellar rotation (if possible) • Low or well modeled interstellar extinction • Brightness matched to JWST instrument sensitivities
  5. Cycle 1 “slim” program 1) Calibrate all instrument modes Observe

    one star of each type in all modes (3 total) Reliance on a single star has not worked well (e.g., Vega) 2) Establish the average calibration Observe larger sample with selected modes NIRCam/MIRI Imaging, NIRSpec/NIRISS/MIRI spectroscopy Diagnose/correct for variations not in models Min of 3 stars per type (must include all from part 1) 3) Repeatability Observe one star approximately once/month Empirically measure detector/instrument/telescope uncertainty Only one filter/grating per detector
  6. “Slim” is just the beginning Slim provides – ~3 stars

    per mode (some modes have more) STScI end-to-end error budget – Assumes 2% uncertainties for an individual star • Each star is unique at some level • From Hubble calibration experience – Number of standards needed for budget • 12 NIRCam/MIRI/NIRISS • 5 NIRSpec Achieving error budget – Requires more stars/observations in future cycles
  7. Which stars for “slim”? Picked to optimize the overlap between

    instruments and modes – Observing efficiency and cross-calibration Fewest targets possible to achieve the slim program goals Use S/N target of 200 – 0.5% measurement uncertainty
  8. Summary NIRCam – Imaging • 1 WD, 1 A, 1

    G (all) • 3 WD, 3 A, 3 G (wide filters) – WFSS: 1 WD, 1 A, 1 G – Coronagraphy: 1 WD, 1 A, 1 G NIRSpec – IFU: 1 WD, 1 A, 1 G – FS • 1 WD, 1 A, 1 G (all IFU/FS_S1600A1) • 3 WD, 3 A, 3 G (Prism) NIRISS – SOSS: • 1 WD, 1 A, 1 G (all) • 5 A, 4 G (2.5 um) – WFSS: 1 WD, 1 A, 1 G – Imaging: 1 WD, 1 A, 1 G – AMI: 1 A, 1 G MIRI – Imaging: 3 Hot, 8 A, 7 G – MRS: 3 A, 3 G – LRS slitless: 3 A, 3 G – LRS slit: 2 A, 1 G – Coronagraphy: 2A, 2 G
  9. Cross-mission calibration All standards have or will be observed –

    Hubble/STIS (UV+optical) Most with – Spitzer/IRAC 3.6 micron Subset with – Hubble/WFC3 NIR grism (1–1.6 micron) – Spitzer/IRAC and MIPS (4.5 to 24 micron) – TESS ~weeks variability measurements
  10. Total time ~318 hours Parts 1 and 2 (calibration+average) –

    White dwarfs: ~78 h – A-type stars: ~102 h – G-type stars: ~94 h Part 3 (repeatability) – 10 repeats: ~44 h AbsFlux program inherently multi-instrument – Improves fidelity of calibrators – Improves observing efficiency
  11. JWST AbsFlux program High quality flux calibration for all instruments

    Inherently cross-instrument & cross-observatory Will quantify the random & systematic uncertainties Based on expertise from the absolute flux community
  12. Additional information Reports – STScI End-to-end Error Budget • Gordon,

    Boyer, Muzerolle, Sloan, & Volk, 2019, JWST-STScI-001007 Rev C – JWST Absolute Flux Calibration II: Expanded Sample of Primary Calibrators • Gordon & Bohlin, 2012, JWST-STScI-002540 – JWST Absolute Flux Calibration I. Proposed Primary Calibrators • Gordon, Bohlin, Fullerton, Beck, & Robberto, 2009, JWST-STScI-001855 Selected Papers – A New Stellar Atmosphere Grid and Comparisons with HST/STIS CALSPEC Flux Distributions • Bohlin, Szabolcs, Gordon, et al. 2017, ApJ, 153, 234 – Spectral Calibration in the Mid-Infrared: Challenges and Solutions • Sloan, Herter, et al. 2015, AJ, 149, 11 – Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared • Bohlin, Gordon, & Tremblay 2014, PASP, 126, 711 – Absolute Flux Calibration of the IRAC Instrument on the Spitzer Space Telescope Using Hubble Space Telescope Flux Standards • Bohlin, Gordon, Rieke, et al. 2011, AJ, 141, 173 – Absolute Physical Calibration in the Infrared • Rieke, Blaylock, Decin, et al. 2008, AJ, 135, 2245 – Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. II. 70 μm Imaging • Gordon, Engelbracht, et al. 2007, PASP, 119, 1019 – On the calibration of the IRAS low-resolution spectra • Volk & Cohen 1989, AJ, 98, 1918