Subject: Brief Astrometric Update

From: Dave Monet

Submitted: Fri, 8 Nov 2002 10:25:08 -0700

Message number: 20 (previous: 19, next: 21 up: Index)

Michael's mailbox appears to be too empty, so I am sending the following,
mostly astrometric update to the whole SWG.  I hope that a better mechanism
will be created for astrometric working group discussions.

  1) Next week (Nov 11-16) is the Pan-STARRS Data and Science working
     group meeting in Honolulu.  Obviously, most of their astrometric
     issues are of direct interest to the LSST science case, and I am
     going with the intention of contributing and learning.  Presumably,
     Kaiser et al. will be submitting a summary to LSST after most
     of the blood has been cleaned up.

  2) The single most important issue for planning LSST astrometry is
     understanding what the uncertainty of a single observation will be.
     My hope is to cut some sort of a deal with various IfA/Pan-STARRS
     folks who have access to large aperture telescopes and wide
     field cameras to get some engineering data from short exposures.
     I think that I understand the theory of seeing well enough by now,
     but I think that some observations will add credibility to the
     science case.  Indeed, there may be big differences between the
     Pan-STARRS ~60 sec integrations and the LSST's ~6 sec integrations.

  3) I am still trying to figure out how to get astrometric engineering
     data from the various sensors that might go into LSST.  It would
     be nice to collaborate with folks who have OTCCD, high resistivity
     CCD, and/or CMOS hybrid sensors.  I would be glad to do the scut
     work if folks have or can connect me with such data.

  4) Geoff Marcy reminded me that Pan-STARRS/LSST data mining for
     astrometric wiggles ought to be very exciting.  I have tried to
     flesh out estimated counts, but binary star astrometry is yet
     more arcane than positional astrometry.  So far as I can tell,
     there are 5 known systems with a>0.7 arcsec with P<20 years,
     and there are about 1200 systems with P<20 years that have
     any sort of known astrometric wiggle.  The really exciting
     prospect that Pan-STARRS/LSST will get astrometric data on
     all stars, so a wiggle-based study of late M, L, and T-dwarfs
     (just to name a few) can be done in a well-defined manner.
     Pan-STARRS (and LSST given how things are going) might provide
     important targets for the SIM mission.

I encourage all (and not just the astrometry folks) to send me astrometric
cares and concerns.  If nothing else, I can act as a clearing house for
needs, observations, and simulations.  My current Rules of Engagement start
with nailing down (with any luck to better than a factor of 2) the mean
error of unit weight for local and global astrometric accuracy for something
like LSST's detector and cadence.  This is the rock upon which we will
build the astrometric science case.

-Dave Monet is dgm@nofs.navy.mil

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