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

Attendees: Darren DePoy, Pat Osmer, Paul Byard, Chris Morgan, Tom O'Brien, Mark Derwent, Dan Papallardo, Chris Morgan, Jerry Mason, Bruce Atwood, and Rick Pogge.

Optics

BK7 tests with the lab CCD showed that the beta-decay electron effect is bad, bad enough (~3x over background) that BK7 is unacceptable as a red camera dewar window/field-flattener material. We therefore are switching to NZK7, but are having problems getting a piece in the size and characteristics we need from Schott.

Ohara has an equivalent glass (like Schott FK51) that has the same error function as NZK7 (very symmetric). It is a fluoride glass, but Steve Miller tells us that it tends to be fragile and hard to work. Further study of this issue suggests that it is a generic problem with this glass, and so it is likely unsuitable for use in this optic. We will explore our options and reach a final decision later this month.

AGW Specification

Darren has circulated a draft specification for the AGW performance for MODS to help us understand what kinds of cameras will be acceptable. This document is only being circulated internally now. Darren will be going to Tucson in a couple of weeks for a long observing run and will talk to the Steward people about their cameras as one option. In the meantime, Chris Morgan has been tasked with exploring various commercial TEC-cooled CCD camera options, and working with Rick to simulate centroiding performance.

Mechanical Design & Fabrication

Tom has finished designing the AGW stages, up to the point where further design requires we have the specifications of the cameras decided upon, and their optics specs. The real-estate in the instrument is well-defined in terms of what we need to have the mechanisms avoid hitting. Above the slit is very clean and presents no particular problems and has a lot of vertical volume available in which to package cameras. Below the slit is very tight and presents us with challenges.

Calibration System

Paul has designed the calibration system optics using an integrating sphere with a 100mm port and mask and a lens that is positioned in front of the focal plane to deliver a pseudo-pupil image to the grating. Working with Tom, they have a preliminary mechanical design in which the integrating sphere is mounted "side looking", and calibration light is fed to the focal plane via an insertable pickoff mirror mounted on a 2-position stage. The calibration mirror insertion mechanism doubles as the instrument entrance cover, so that calibration light from this system will not spill out of MODS while in use.