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NOAO Newsletter - CTIO Operations - March 2000 - Number 61


The First Semester of the NOAO MOSAIC II Camera at CTIO

R.A.Schommer (rschommer@noao.edu), R.C. Smith (csmith@noao.edu), A. Walker (awalker@noao.edu), and K. Olsen (kolsen@noao.edu) for the Mosaic II Team

The Mosaic II camera was successfully commissioned at CTIO in July 1999. Shared-risk observing starting in August produced useful images from the first night, and observers have taken home some excellent data over the past five months. Guided images in red bandpassses have been obtained with FWHM < 0.7" over > 600 sec.


Caption: Photo credit: M. Shara (Am. Mus. of Nat. History), D. Zurek (STScI), and R. Schommer (NOAO)

In summary, the Mosaic II offers a 36" x 36" field, with 0.27"/pixel in an 8K x 8K mosaic of SITe 2K x 4K CCDs, and is a clone of the Mosaic I camera, which has been in use at KPNO for 2.5 yrs.

Please check the web pages for details and updates (http://www.ctio.noao.edu/mosaic). The camera is currently in our La Serena labs for upgrades and maintenance between semesters, and is scheduled to be reinstalled at the Blanco prime focus at the end of February 2000. We hope to have dual-channel readout working at that time, so that 16 amplifiers will allow complete image readout and delivery time of less than 100 sec, about 1.5x faster than currently available.

Our experience with data reductions is still somewhat limited, but the advice is to get more disk space and a faster computer. Typical raw images from one night fill 5-10 gigabytes. Processing is very CPU and disk intensive (each image is, of course, 16x bigger than that of a 2K chip), so even overscan subtraction and median processes run at coffee-break rates. We have generally found that dome flats are useable to about 1-1.5% for large-scale flattening --- to do much better probably requires careful creation of superflats from multiple sky exposures. CCD reductions and experience indicate that standards should be taken on every chip for careful (< 1%) photometric reductions, as the chips have their own individual properties, such as slightly different sensitivities and color terms. Check our web pages and those of the KPNO mosaic for more comments about data reductions and camera characteristics.

We are collecting an image gallery for public viewing and access, so observers who have processed images should send us their final images if suitable. We currently are featuring multicolor images of Sculptor group galaxies (NGC 247 and NGC 300) as part of Cepheid and globular cluster searches, some deep R and I band imaging of high redshift SNe (z = 0.45-1.0) as part of a cosmology program, and a spectacular U-band image of an LMC field, showing some SNe remnants (OII emission), and giving 1" FWHM images in about 1 hour of stacked integration time (see attached figure, courtesy of Mike Shara, Am. Mus. of Nat. History and David Zurek, STScI).


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