16559

Monitor sensitivity of each MAMA grating mode to detect any change due to contamination or other causes. Also monitor the STIS focus in a spectroscopic and an imaging mode. Obtain exposures in each of the 2 low-resolution MAMA spectroscopic modes every 4 months comma in each of the 2 medium-resolution modes once a year comma and in each of the 5 echelle modes every 3 months comma using unique calibration standards for each mode comma and ratio the results to the first observations to detect any trends. In addition comma each L-mode sequence will be preceeded by a CCD-F28X50OII image comma two spectroscopic ACQ-PEAKs with the CCD-G230LB and crossed linear patterns comma and two CCD-G230LB spectra comma with the purpose of measuring the focus (PSF across the dispersion as a function of UV wavelength) and each M-mode sequence will be preceded by a CCD-F28X50OII direct image also to monitor the focus. Beginning in Cycle 27 comma WFC3 parallel observations have been added to all echelle visits to monitor focus contemporaneously.