Subject: Pre-telcon Astrometry

From: Dave Monet

Submitted: Thu, 24 Apr 2003 09:29:37 -0700

Message number: 116 (previous: 115, next: 117 up: Index)

Let me start this effort (intended to keep Michael happy) with a comment,
and then pass on to the Astrometry input to the cadence, etc.

  Comment:  If we insist fixing on the LSST cadence 8 years before
            we use the telescope, I think that we are making a
            big mistake.  Maybe my brain has turned to mush with all the
            discussions (good, bad, indifferent), but it seems that the
            costed proposal, due 18 months from now, does not require
            that this issue be settled.  Rather, the proposal should
            identify the various cadences of interest, and show that the
            proposed system can operate efficiently using them.

And now on to what I think Michael is requesting.

   Survey Cadence:
            1 visit per lunation per color.  This is driven by
                 the need to monitor all of the stars for astrometric
                 wiggles as a function of color so that we can attempt
                 to resolve the stars involved.

            2 visits per lunation in one survey color during the first
                 year.  This is driven by the desire to get an inventory
                 of the stars within 10pc during the first year, and
                 deliver this as a product to the user community.

            Observations must be taken with |HA| < 1h, at least during
                 the first year.  This is driven by the need to fit and
                 remove the effects of DCR.  With luck (and hard work),
                 we might be able to "save" observations farther off
                 the meridian and/or taken with wider passbands once
                 we develop a calibration.  A wider, solar system filter
                 would be useful, but its astrometric utility might be
                 compromised by the solar system cadence and DCR.

   Survey Filters:
            Proposed Sloan g', r', i', z' is fine, and adding Y' would
                 be better.  Extended red sensitivity enables looking
                 for intrinsically cooler objects.

            ND filter.  I hate to raise this to the level of a Requirement,
                 but I think that we must consider LSST in the fabric of
                 catalogs and systems available to the community.  It
                 would be unfortunate if the stars fainter than 18
                 had mas-class astrometry and 2% photometry when the stars
                 from 12 to 17 did not.  Maybe this will go away if
                 Pan-STARRS or other projects succeed, but LSST should
                 not forget this issue.

   First Year:
            1 visit per field in extended set of filters.  This is
                 driven by the need to use multicolor photometry to
                 isolate various stellar populations (once) so that
                 the survey astrometry can provide better input to
                 Galactic structure studies.

            10 (+/-) visits per field in one survey color using an
                 ND=5 (or other magnitude compensation).  This is
                 driven by the need to tie the survey astrometry to
                 the system of bright stars defined by Hipparcos.
                 Note: this need may go away if the required astrometric
                 catalogs are provided to LSST by some TBD program.

As I have noted several times in the past, the Astrometry needs are
satisfied by almost all of the proposed cadences, filter sets, and
telescope designs.  I did not insert a requirement on image quality
of phtometricity (is this even a word?) since I think that Astrometry
would be happy with any of the proposed designs.

I have deliberately not passed this by the Astrometry working group
before spamming lsst-general.  If people complain or have any sort of
comment, I think that these should be sent to the entire group.  As
Michael noted, lsst-general is in Lone Ranger mode: it too quiet, Kimosabe!

-Dave Monet is dgm@nofs.navy.mil

LSST LSST LSST LSST LSST    Mailing List Server   LSST LSST LSST LSST LSST LSST
LSST
LSST  This is message 116 in the lsst-general archive, URL
LSST         http://www.astro.princeton.edu/~dss/LSST/lsst-general/msg.116.html
LSST         http://www.astro.princeton.edu/cgi-bin/LSSTmailinglists.pl/show_subscription?list=lsst-general
LSST  The index is at http://www.astro.princeton.edu/~dss/LSST/lsst-general/INDEX.html
LSST  To join/leave the list, send mail to lsst-request@astro.princeton.edu
LSST  To post a message, mail it to lsst-general@astro.princeton.edu
LSST
LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST