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JWST ABSOLUTE FLUX STANDARDS

JWST ABSOLUTE FLUX STANDARDS. 2010 July 23. Accuracy Goal: 1% at 0.8-30µm. Three types: WD, A, G. Tlusty NLTE for WDs. Fit models to STIS and NICMOS fluxes for A & G stars. Solar Analogs. HST/IRAC Fluxes. SUMMARY One 4σ WD deviation: Model or photometry error?

dorothy-williamson
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JWST ABSOLUTE FLUX STANDARDS

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  1. JWST ABSOLUTE FLUX STANDARDS 2010 July 23 Accuracy Goal: 1% at 0.8-30µm. Three types: WD, A, G. Tlusty NLTE for WDs. Fit models to STIS and NICMOS fluxes for A & G stars.

  2. Solar Analogs

  3. HST/IRAC Fluxes

  4. SUMMARY • One 4σ WD deviation: Model or photometry error? • 2. Results of ~2% lower than the Reach et al. 2005 calibration are understood to 1% for the A and G stars. • 3. Rieke et al. 2008 suggest a 1.5% higher IRAC calibration. • 4. Better grids of models are needed, especially for A stars. • --MARCS goes only to 20µm and to 8000K • --CK04 grid has coarse sampling, especially in the IR and • does not match the Kurucz special solar model to 1% • --NextGen-Phoenix lines are too strong by up to ~20x • 5. Can the observations be matched to ~1% in regions of heavy line-blanketing?

  5. Current Status A and G star papers are published Draft of Spitzer cal paper is complete13 STIS orbits approved for cycle 174 Nicmos orbits for faint V=17-18 G-star photometry complete for 12 stars in 2-3 filters

  6. Future Work1. Plan sample cal observations for each JWST instrumental mode to see if the dynamic range of standard stars is sufficient2. Refine the model fitting and expand the CALSPEC database of flux standards: a) Collect sets of better models for G and A types and try to understand differences at the 1% level. b) Add the Spitzer 3.6-24 micron photometry as constraints to the fitted models. c) Investigate the new Bergeron NLTE WD models for pure hydrogen and precise physics of line profiles.

  7. 1. Primary WDs: G191B2B, GD71, GD1538 see eg: Bohlin 2007, in ASP Conf. Ser. 364, 315; also Astro-Ph 0608715 Supplemented by LDS749B - Bohlin, & Koester 2008, AJ, 135, 1092 2. A type Stars 6 IRAC Standards (Reach et al. 2005) observed by NICMOS from 0.8-2.5mic are modeled, and the Cohen SEDs are refined in Bohlin, R. C., & Cohen, M. 2008, AJ, 136, 1171, NICMOS Spectrophotometry and Models for A-Stars ---STIS (0.3-1mic) approved for HST Cycle 17 3. G type Stars 4 Bright (P041C, P177D, P330E, & HD209458) and 3 faint stars already observed by STIS & NICMOS. Bohlin, R. C. 2010, AJ, 139, 1515, HST Spectrophotometry and Models for Solar Analogs 4. Cool Stars STIS + NICMOS SED exist for KF06T2 (K1.5III),VB-8 (M7), 2M0036+18 (L3.5), & 2M0559-14 (T5). A collaborator for modeling with the 2.5-30micron flux prediction would be nice.

  8. WDs

  9. A-stars

  10. Vega

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