The collections of spectral energy distributions (SEDs) in the \emph{Hubble Space Telescope} (HST) CALSPEC database are augmented by 19 IR SEDs from Wide Field Camera 3 (WFC3) IR grism spectra. Together, the two IR grisms, G102 and G141, cover the 0.8--1.7~\micron\ range with resolutions R=200 and 150, respectively. These new WFC3 SEDs overlap existing CALSPEC Space Telescope Imaging Spectrograph (STIS) standard star flux distributions at 0.8-1~\micron\ with agreement to ≲1\%. Some CALSPEC standards already have near-IR camera and multi-object spectrogragh (NICMOS) SEDs; but in their overlap region at 0.8--1.7~\micron, the WFC3 data have better wavelength accuracy, better spectral resolution, better repeatability, and, consequently, better flux distributions of ∼1\% accuracy in our CALSPEC absolute flux SEDs vs. ∼2\% for NICMOS. With the improved SEDs in the WFC3 range, the modeled extrapolations to 32~\micron\ for JWST flux standards begin to lose precision longward of the 1.7~\micron WFC3 limit, instead of at the 1.0~\micron\ long wavelength limit for STIS. For example, the extrapolated IR flux longward of 1.7~\micron\ for 1808347 increases by ∼1\% for the model fit to the data with WFC3, instead of just to the STIS SED alone.
@article{arxiv.1903.11985,
title = {CALSPEC: WFC3 IR Grism Spectrophotometry},
author = {Ralph C. Bohlin and Susana E. Deustua},
journal= {arXiv preprint arXiv:1903.11985},
year = {2019}
}