Subject: LSST Astrometric Survey

From: Michael Strauss

Submitted: Wed, 9 Oct 2002 11:13:18 -0400 (EDT)

Message number: 8 (previous: 7, next: 9 up: Index)

Hello all,
  Let me second Dave's suggestion that astrometry be raised to a
primary scientific driver of the LSST.  In addition to the parallax
survey he mentions, proper motion studies over the timeline of the
LSST will be of tremendous scientific import.  And all the asteroid
studies will benefit greatly from accurate relative astrometry. 

  Having said this, I would like to hear more about the rationale
behind Dave's number of 30-50 mas absolute astrometry on a single
observation.  In the 8.4m design, the exposure time is 10 seconds,
which is short enough that atmospheric refraction effects completely
dominate the astrometric residuals.  With SDSS (55 second exposure
time), and using the UCAC dense network of standards, it was my
understanding that the residuals are roughly 60 mas per coordinate,
rms.  I don't know how this number will increase with a 1/5-as-long
exposure time, but it will certainly be higher. 

			   Thanks,  Michael

				  

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