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

Attendees: Darren DePoy, Bruce Atwood, Dan Papallardo, Paul Martini, Jen Marshall, Ray Gonzalez, Paul Byard, Jerry Mason & Rick Pogge. Tom and Mark are at Indian Creek checking out progress on the MODS2 structure.

MODS Optics

Paul presented a progress report on the MODS blue camera corrector lenses that he received from Steve Miller at SOML. So far they have profilometry across the optic (18-point radial scans at 10-degree intervals using a pick-point method), which they combine to contruct 2D profiles to be fit with a 15th order Zernicke polynomial. From these they derive an estimate of the overall figure and attempt to construct a structure function. Two problems with this at present is that they don't have much resolution on the smaller scales of interest, and they haven't beaten down the errors to the point that optical testing can become effective. In the last 3 months they have halved the peak-to-peak errors from 10-13microns to 5-6microns. The surface errors will need to be more like 1-3microns before optical testing can proceed with the null lens and interferometer. If past performance is a guide (and is linear) this should require another 3 months, then perhaps another 2-3 months of work finishing and then turning over the optic to grind/polish the other side and do the final acceptance tests before cutting the parts from the parent.

This means we are looking at a minimum of 5-6 months before we can expect delivery of the blue camera corrector lenses (i.e., not until late-winter/early-spring 2006). Jerry Mason has been tasked with putting this new estimate into the schedule to assess the impact. We still do not have estimates of the interval between delivery of the blue correctors and completion/delivery of the red correctors. Hopefully lessons learned from the blue correctors will speed that process.

In other things, Paul has been working on the R=8000 grating design. The new ruling he has been exploring is a single grating that will work in 1st- and 2nd-order in the red, and 3rd-order in the blue. Paul showed us efficiency curves (including the dichroic and CCD QE curves). He has been asked to make a second set of plots showing the grating-only efficiencies so we can compare the orders w/o confusion with the combined dichroic and CCD efficiencies. So far, the 2nd-order red and 3rd-order blue look reasonably good, but we sacrifice thruput in the far blue because of the narrower 3rd-order blaze function (dies rapidly from ~40% at 400nm to <10% at 350nm). We need to assess the science impact of this compared to other grating options, but given what Richardson refused to bid on earlier, getting high efficiency and R=8000 in the far blue may be very difficult/impossible. More later...

CCD Dewars

Bruce reported briefly on discussions with one of the candidate dewar vendors, and discussions with recent customers of that vendor. It looks like of the 3 bids we received, we have two very good prospective vendors, and Tom, Bruce, and Darren are tasked with making a decision and getting an order out his week.

New ISL Positions

After numerous administrative delays at the college/university level, we are now free to advertise for two new position in the instrument group:

1. Electronics Technician/Junior Engineer
2. Optical Engineer