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Session 14 - Real Calibrations.
Display session, Monday, June 08
We present the first results of the on-orbit spectroscopic flats for the STIS CCD. The goals of this on-going programme are to: a) obtain flats at each wavelength setting each for the low-resolution G430L and G750L gratings; b) obtain flats at each wavelength setting for each of the G430M and G750M gratings; c) obtain flats at the G430L grating at GAIN=1 and GAIN=4 to monitor any gain dependent effects; and d) to monitor variability of the tungsten lamp over time. The programme will allow us to construct, over the lietime of the proposal, a library of high signal-to- noise ratio (\sim 100) spectroscopic flats from on-orbit data. We have developed a script using pre-existing IRAF/STSDAS tasks that will allow us to flatten our data to better than 0.5%, and which, we anticipate will allow us to obtain flattening to better than 0.1% as more epochs are obtained. The technique uses two independent linear spline fits in an iterative fashion allowing for the masking of hot pixels that are not removed from the data by cosmic ray rejection. We find no gain dependent effects, and a moderate variation in the brightness of the tungsten lamp. The overall shape of the flats stay constant (to better than 2%) on data for which we have more than one epoch. As each of these are flats constructed, they will be delivered to the calibration archive and used for routine pipeline calibrations, replacing the current ground-based flats.
Program listing for Monday