16439

We aim to measure the time dependent sensitivity loss for WFC3-IR using spatial scans of the open cluster M35. We use spatial scanning as the SNR achieved from scanning is higher than conventional staring observations. The spatial scans build on the F140W observations performed in HST program 14020 and the F140W and F098M observations performed in HST program 16031. The observations are performed over two identical visits virgul3 months apart and the observation structure in each visit is also identical with that executed in program 16031. The proposed data will extend the existing baseine by virgul1 year and the short interval between the visits will provide additional sampling for the short-term repeatability analysis.