To: 3.5m users From: Jon Holtzman, Jon Morse Re: SDSS z filter for NIC-FPS camera As most of you know, CU is building a near-IR camera (+ Fabry-Perot) for the 3.5m. A relatively small amount of 3.5m CIF funds have been set aside to provide some "enhancements" to the baseline instrument. At the Seattle AAS, significant interest was expressed to obtain a SDSS z filter for the new camera, and CU would like to proceed with the purchase of such a filter. (NIC-FPS filters are 65mm round and operate at 77K. CU already has in its possession Mauna Kea consortium J, H, and Ks filters.) However, some choices are required about the details of such a filter. In the SDSS survey, the long-wavelength end of the z filter is defined by the CCD response, which gradually tails off from 0.9-1.1 microns; the short-wavelength end is relatively sharp and defined by the filter. In a near-IR camera, the filter must provide the long-wavelength cutoff. At the short wavelength end, the bandpass will be defined either by the filter or by the short wavelength cutoff of the IR detector; the quoted short cutoff response of the Rockwell detector appears to match the short wavelength cutoff of the SDSS z filter rather well. This leads to a choice: 1. Try to construct a filter that mimics the response dropoff of the SDSS CCDs as well as possible in an attempt to match the SDSS bandpass. Advantages: potentially allow NIC-FPS z measurements to be accurately transformed to the SDSS system, although how accurately this can be done is still somewhat questionable Disadvantages: expensive (preliminary quote from Barr of ~$20k), likely difficult to closely match SDSS to within a few percent, gradual slope of long wavelength cutoff results in lower throughput 2. Construct a simpler (square) filter with a sharper long-wavelength cutoff. Advantages: cheaper (~$11k), provides "cleaner" bandpass, e.g. for use in photometric redshifts, higher throughput (depending on choice of long wavelength cutoff Disadvantages: likely to be difficult to obtain good transformations to standard SDSS z, especially for objects with non-standard colors Please note that this is a SDSS z filter in a near-IR camera that might be used when extending studies into the near-IR; a SDSS z filter already exists for use in SPICAM, which is likely to be a reasonable match to the SDSS z bandpass. We solicit input about this decision; please send any comments you have to both holtz@nmsu.edu and morsey@casa.colorado.edu APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 663 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO