HST/WFC3 In-Orbit Grism Performance

The Wide Field Camera 3 (WFC3) is fitted with three grisms for slitless spectroscopy. In the UVIS channel there is one grism, G280, for the near-UV to visible range (200 400nm; 1.4nm/pix). The IR channel has two grisms: G102 for the shorter (800-1150nm; 2.45nm/pix) and G141 for the longer (1100-1700nm; 4.65nm/pix) NIR wavelengths. Using SMOV and Cycle 17 calibration data taken on WR stars, planetary nebulae and flux standard stars, we have assessed the performance of the grisms. We have measured the field-dependent trace locations and dispersion solutions and determined the throughputs. The trace and wavelength solutions for the IR grisms were found to be linear functions, varying smoothly across the field-of-view. The UVIS grism exhibits a highly bent trace and significantly non-linear dispersion solutions. The maximum throughputs for the G102 and G141 grisms, including the telescope optics, are 41% at 1100 nm and 48% at 1450 nm, respectively. Limiting magnitudes at S/N=5 and a 1h exposure are JAB=22.6 and HAB=22.9 for the G102 and G141 grisms, respectively. The results are published as sensitivity and configuration files that can be used with the dedicated extraction software aXe to reduce WFC3 slitless data.