July 28, 1995 Hello all, One of the (many) unknowns facing us as we thrash out the selection criteria for QSO candidates for the SDSS is the colors of known quasars in the SDSS color system. There is a program planned for the fall to get colors of known quasars using the Monitor Telescope, but the smallness of this telescope and the lack of guiding ability preclude using it for QSO's much fainter than 16 or 17 (or at least that is my understanding; please correct me if I'm wrong). It has been suggested that we use the Drift Scan Camera on the 3.5m telescope to carry out a similar program, for fainter quasars. Telescope proposals are due (at least in Princeton) in a few days, so it is rather late to bring this up, but I would like to know if people are interested in such a program. In particular: 1. Is this program worth doing in the first place? One could argue that given QSO photometry in UBVRI, say, the transformation to the SDSS system, to the accuracy we need it (which may not be very high, 0.2 mag may be adequate) is straightforward. On the other hand, the number of quasars with good multicolor photometry in the literature may be small. One could also argue that existing models of QSO SED's (as carried out by Don Schneider; he has gone quite a bit further than what is described in the Grey Book) may be adequate. 2. If the answer to this is yes, how many quasars would be useful to do? I believe plans are to do of the order of 30 QSO's with the monitor telescope. I suspect that multi-color photometry of 100 well-chosen QSO's over a range of redshifts would tell us much about where quasars lie in multi-color space. 3. Is the APO 3.5m DSC the best instrument for the job? The answer to this may be that it is the only instrument for the job, being the only telescope (other than the MT) on which there exists an SDSS filter set. This program is clearly impractical until the filter wheel for the DSC is completed; Tim McKay tells me that we can (somewhat optimistically) hope for early October, which is the beginning of the fourth quarter for which we are applying for time now. 4. If the answer to this is yes, are there people who think this is worthwhile enough to give telescope time? I suspect we're talking about a few nights of photometric weather, which need not be dark (unless we start talking seriously about going to very faint QSO candidates, say fainter than 19th). Let us get some discussion going. I apologize that I am bringing this up at this late date, but I hope that there are enough people interested in this program that we can apply for a meaningful chunk of time. Michael Strauss APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 3 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