Michael Strauss suggests that we use the 3.5-m, plus DSC, to measure the colors of about 100 QSOs in the SDSS passbands. Let me try to work out the amount of time we'd need to do that... One problem is that the filters must be changed by hand, at least, until we get a filterwheel. In that case, let's say that the best way to work is to take images of a set of, say, 10 QSOs in the same filter, then switch filters and go back over the same set of 10, then switch filters, etc. How long would this take? Let's assume we can: - slew from one object to another in 1 minute - don't need to take acquisition pictures - use the DSC in "stare mode", to avoid ramp-up and -down - take 120-second exposures, and can transfer the image to the computer while slewing to the next object - switch filters in 5 minutes Then, in order to acquire ugriz images of a set of 10 QSOs, we must allow 10 x 2 minutes for exposures in each band 10 x 1 minute for slewing to next object, each band ----------------- 30 minutes for set of 10 images in each band x 5 passbands ----------------- 150 minutes for ugriz measurements of 10 QSOs In addition, we really must take ugriz measurements of, let us say, one field of standards in each passband at the start and end of each passband; that is, we would follow a sequence like this: switch to next filter take image of standard field take images of 10 QSOs take image of standard field switch to next filter ... That adds 6 minutes per passband to the above numbers: 150 minutes for ugriz measurements of 10 QSOs 30 minutes for ugriz measurements of 1 standard field ---------------- 180 minutes for complete set of observations At 3 hours for a set of 10 QSOs, it would take 30 hours to complete a study of 100 QSOs. I suspect that this is a larger amount of time than people would be willing to devote to the project. Or is this important enough that we want to do it? Michael Richmond APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 5 in the apo35-general archive. You can find APO the archive in /u/strauss/apo/mailer/apo35-general on astro.princeton.edu 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