The Ohio State University College of Mathematical & Physical Sciences Department of Astronomy

Attendees: Pat Osmer, Bruce Atwood, Paul Byard, Tom O'Brien, Mark Derwent, Darren DePoy, Jen Marshall & Rick Pogge,

Optics

Paul reported results of calculations of the amount of slit curvature we can expect on the CCD in the R=8000 and R=2000 spectral modes. These calculations focussed on the blue camera, but apply analogously to the red camera. The R=8000 grating parameters are based on a straw-man design we are working up for a potential new ruling, whereas the R=2000 parameters were based on an available Thermo/RGL stock ruling we will use for MODS.

As expected, the amount of slit curvature (how a monochromatic image of the long slit maps onto the CCD) varies with dispersion, and amounts to 225-microns of center-to-edge curvature on the CCD (the edge is 3-arcminutes from the center on the sky). This amounts to 15-pixels of bowing of the slit. It is slightly more at one end of the R=8000 free spectra range than another. From experience (e.g., Rick and Pat), this is not outrageous and could be taken out in the reduction, though care will be required. The software/procedures required already exist in current reduction packages (IRAF/MIDAS/XVista), so no new development is required, but during commissioning how the cope with it will be part of the delivered data reduction manual/guidelines.

As expected, at R=2000 the effect is less, and well within what could be dealt with in software.

The next meeting will be in October, time to be determined. Note also that OSU hosts the LBT Board Meeting on October 21.

R. Pogge, 2001 September 26