From novak@belmont.astro.nwu.edu Sat Jul 1 00:24:01 2000 Date: Tue, 20 Jun 2000 11:42:34 -0500 (CDT) From: Giles NovakTo: "Griffin, Greg -- Greg Griffin" Cc: David T. Chuss Subject: grid test guidelines Greg, Thought you might appreciate a bit of guidance on how long we need to integrate when doing the grid tests. of course it depends on the weather. Let me give you some guidelines that can help you to decide. (1) for the wires at 45 degrees to the vertical, we want polarimetric signal-to-noise of about 10:1. That's pretty much the same as photometric signal-to-noise of 14:1. So make a guess as to how long it would take for you to detect the peak at a signal to noise of 14:1 and spend about that much total time on the polarimetry. In tau=2 weather I'm guessing it will take you ten minutes or so (one scan). Do three scans to be safe, perhaps. In tau=3 weather I'm guessing it will take you four hours of observations - if you can even find the source ! But if you get a week-long stretch of tau=3 you will get bored and will want to start doing grid tests just to get them out of the way. (2) for the wires horizontal (or did you say vertical? - it doesn't matter which as long as you write it in the log when you do it) we need only 5:1 polarimetric signal-to-noise as this is just a crude check that things move the right way in the polarization signal. So one ten-minute scan in tau=2 weather should be plenty. Or an hour or two in tau=3. The most important thing for the grid test is you write in the log exactly how the wires appeared to you when viewed from a specific perspective, etc. thanks, Giles