Subject: Any interest in using the 3.5m for a photometric survey of known QSO's?

From: Michael Strauss

Submitted: Fri, 28 Jul 1995 13:36:10 -0400

Message number: 3 (previous: 2, next: 4 up: Index)

				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
			Michael Strauss

APO APO APO APO APO  Apache Point Observatory 3.5m  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
APO  To join/leave the list, send mail to
APO  To post a message, mail it to