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

2. Solar
Analogs

4. HST/IRAC
Fluxes

5. SUMMARY One 4σ WD deviation: Model or photometry error?
2. Results of ~2% lower than the Reach et al calibration are understood to 1% for the A and G stars.
3. Rieke et al 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?

6. Current Status. A and G star papers are published
Current Status A and G star papers are published Draft of Spitzer cal paper is complete 13 STIS orbits approved for cycle Nicmos orbits for faint V= G-star photometry complete for stars in 2-3 filters

7. Future Work 1. Plan sample cal observations for each JWST instrumental mode to see if the dynamic range of standard stars is sufficient 2. 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 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.

8. 1. Primary WDs: G191B2B, GD71, GD1538 2. A type Stars 3. G type Stars
see eg: Bohlin 2007, in ASP Conf. Ser. 364, 315; also Astro-Ph
Supplemented by LDS749B - Bohlin, & Koester 2008, AJ, 135, 1092
2. A type Stars
6 IRAC Standards (Reach et al. 2005) observed by NICMOS from mic 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), 2M (L3.5), & 2M (T5). A collaborator for modeling with the micron flux prediction would be nice.

9. WDs

10. A-stars

11. Vega