Two instrument changes at WIYN will enhance its scientific capability. In Semester 2000A, the "Mini-Mosaic" will become the standard imager and DENSEPAK will be available at all lunar phases.
We are currently commissioning the "Mini-Mosaic" camera for the Imaging Nasmyth Focus at WIYN (see June issue, p 22). This camera utilizes two 2K × 4K SITE chips set side by side to make a 4K × 4K image. The CCDs are nominally identical to the ones used in the MOSAIC camera. The 15 µm pixels project to ~ 0.14" on the sky, so that the not uncommon seeing of 0.5" at WIYN is adequately sampled. We will present performance evaluations in the next Newsletter.
Data taken thus far confirms that these chips, which are flatter than S2KB, provide excellent images across the entire field (9.6' on a side). At 0.5" seeing, changes in the point-spread-function with field position are not significant. The blue and UV throughput is also higher relative to S2KB. The commissioning efforts are now concentrating on a rigorous examination of the photometric performance of this new device. Barring any serious problems, it is expected to be used on a shared risk basis later in 1999B, and will be the standard imaging device on WIYN in Semester 2000A, replacing the S2KB entirely.
"DENSEPAK," the integral field unit (IFU) fiber feed to the WIYN bench spectrograph, has been available only in bright time. The rationale was that since it mounts on and occupies the imaging port, while its other end occupies the bench spectrograph, installing it precludes use of HYDRA as well as direct imaging. Queue observing thrives on a multiplicity of options, selecting the `best' observations to execute, based on proposal priority matched with available conditions. On the other hand, we worry that we may be shutting out pressing projects that require an IFU in dark skies. Thus, in Semester 2000A, DENSEPAK will be available for all lunar phases.
Abi Saha