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

Attendees: Darren DePoy, Paul Byard, Jen Marshall, Pat Osmer, Chris Morgan, Mark Derwent, Jerry Mason, and Rick Pogge.

Cost and Schedule

After getting turned down by TSIP (see 2003 May 28), Darren has been doing a detailed analysis to understand how much money we need to complete a minimal baseline MODS2 on our own. The basic number, subject to refinement, is US$700K, including about $100K of outside machining costs, but not including such items for which we do not have good quotes like optical coatings. Darren will be working to refine this number over the next few months.

Pat and Rick spoke with Todd Boroson at NOAO last Friday to get a formal debriefing for our TSIP proposal. Pat will be traveling to Washington DC to speak with Wayne van Citters and Craig Foltz at NSF (with Todd included via telephone) about this in two weeks.

We do not expect a reversal of the TSIP decision, but we do hope to get a better understanding of what the real conditions of the TSIP program are, and how me might better be able to move ahead with getting funding to complete both MODS spectrographs.

Optics

Paul Byard presented a report on an interesting concept for getting a reasonable very-low-resolution "survey" mode for MODS using an 8-degree double-pass prism in place of a grating. With an 8-degree prism angle and a reflective backside, we can get an effective 30-degree beam out of the DP prism, which allows us to use it like a grating in the existing grating turret without having to introduce any other optics into the system.

The actual performance is limited by the available prism materials. Using Silica in the blue part of the spectrum would deliver resolving powers of 70-300 from 330-730nm wavelengths. The choice of glass for the red part of the spectrum are less obvious: the issues are how to find the best balance of the dispersion and absorption properties of the glasses. Paul is still exploring options (one important proviso is identifying glasses that can be made into prisms of this size with the homogeneity specs we require).

An attraction of this design is that the throughput is much higher than with a grating (as much as 80%), and the cost is relatively low, roughly $15K for materials + working for a Fused Silica prism (or about $30K to make 2 such prisms for both MODS: compare this to $135K for two copies of a replica grating, or $250K for a new master ruling and 2 replicas for each modes).

Paul will continue to explore this design.

Mechanical Design

Tom is out of town. Mark Derwent is working on the bid package for the top structure fabrication (including handling fixtures). He will report back once he hears from the vendor. Negotiations, however, are proceeding very well.