Subject: Towards an LSST Design Reference Mission

From: strauss@astro.princeton.edu

Submitted: Tue, 1 Jul 2003 14:03:56 -0400 (EDT)

Message number: 131 (previous: 130, next: 132 up: Index)

Hello all,
  Traffic on lsst-general, and discussions by the LSST working group,
have been rather sparse lately.  It is time to get things moving
again.  There have been several relevant recent developments.  First,
as you know, there is a similar Science Working Group for the GSMT,
chaired by Rolf Kudritzki; Jeremy Mould tells me that they have just
submitted a document outlining the science case for GSMT to the NSF.
Jeremy, if this document is public, can you point us to it?  Second,
you may have already heard the news that Mike Turner has been
appointed Assistant Director for Mathematical and Physical Sciences at
NSF.  As Mike was chair of the committee that produced the "Quarks to
the Cosmos" report, that among other things identified LSST as a high
priority, this can only be good news for the LSST project.  Mike
starts his new position on October 1; this gives us a meaningful
deadline by which to get a first draft of our design reference mission
out. 

  With this in mind, I plan to spend much of this summer writing, with
input from all the members of the Science Working Group (and indeed,
anyone else who has something to add).  Below please find a suggested
outline for the document that we would produce.  Please send
suggestions/comments on the outline.  More importantly, please send
offers of work!  As you all remember, we left the March meeting in
Tucson with specific writing assignments, making the cases for the
main science drivers which we've identified.  We have something in
hand already from Gary Bernstein on KBO's (lsst-general #114).  I know
that Al Harris, with input from Ted Bowell and various members of the
SWG, has been working hard on his document for the NEA's: Al, where
does that stand?  Chris Stubbs has been promising for some time a
writeup on the variable universe.  I am a bit unclear on where things
stand on the supernova front: Peter Garnavich has told me that he has
specific thoughts on this, but I have yet to see them.  Tony
Tyson has produced some early writeup on weak lensing (lsst-general
#24); this needs to be expanded to include the insights gained from
the discussions in Tucson.  Finally, Dave Monet has produced a number
of vaaluable contributions on the nuts and bolts of astrometry (cf.,
lsst-general 116), and was planning to write up the science case for
the Galactic Structure/stellar populations following the meeting that
was chaired by Knut Olsen on that subject (cf., lsst-general 103).  

Let me suggest that all text that is produced be done in LaTeX or
plain ASCII; this is much easier (for me!) to deal with in putting it
all together than Word, PDF, or RTF.  Figures can be in postscript or
jpeg.  If you have relevant documents that need to be posted that are
in other than straight ascii format, send them to me; I will put them
on a web page here at Princeton, and then we can send a note to
lsst-general telling people the link.  

  OK, here is the outline.  Please let me know your thoughts.  

		  Cheers,  Michael Strauss


Introduction: Scope of this document; charge to the committee; brief
outline of what is to follow.

Desiderata: Brief discussion of mention of LSST in three decadal
surveys, and the range of science that these surveys would like to
see. 

Discussion of figures of merit, both for the telescope as a whole, and
for a given implementation of an observing plan (being sure to keep
the distinction between the two clear).  Note: Tony Tyson is finishing
up a document on the telescope figures of merits, which he will post
shortly to lsst-general. 

Brief discussion of strawman observing plan, to set the stage for the
science discussions. 

  Science drivers (this will be the bulk of it):
      Near-Earth Asteroids: 
		 Discussion of risks as a function of size.
		 Discussion of where we'll be in 10 years. 
		 Need for a complete sample. 
		 Discussion of search strategies, relation to figures
		    of merit. 
		 Concerns (getting orbits with a background of
		   main-belt asteroids, doing photometry off trailed
		   images, etc.)

     Kuiper Belt Asteroids:
	         Science case: Dynamics, physical properties,
					 binarity, etc. 
		 Where we'll be in 10 years. 			 
		 Need for a large sample.
		 Need for color information, light curves. 
		 Search strategies:
			What we can do to 24th mag. 
			What we can do to 26.5 mag. 
	         
    Galactic structure and stellar populations:
	        The science case: 
		   Structure of the Galactic halo
		   Parallax survey complete to 100 pc.
		   Astrometric wobbles 
		   Microlensing?
		LSST and astrometric calibration.
		LSST and photometric calibration. 

    The variable universe:
                 Exploring phase space; the lack of knowledge of the
		    variable universe at the faint end. 
		 Physical arguments for the timescales and amplitudes
		    of variability? 
		 A few specific science drivers: 
		    Novae a la Mike Shara
		    Gamma-ray burst afterglows.  Orphan afterglows?
		    AGN variability
		 Cadences, timescales, and filters

    Supernovae:
             (The SWG hasn't converged on the extent to which we want
	     this to be a major driver.  Peter?  Chris? 
    
    Weak Lensing:
             The science case:
	        A complete census of clusters from z=0 to z=1.
		Measurements of the shear power spectrum.
                (Connect to 'quarks to cosmos' report). 

	     Science goals as function of:
	         Seeing
		 Image Quality
		 Photometric bands

Putting it all together:
	A strawman Design Reference Mission:
	  Static sky vs. variable sky
	  Choice of filters; discussion of cadences. 


	What will remain compelling in the post-Pan-STARRS timeframe.

	A single monolithic telescope vs. a super Pan-STARRS with the
	  same etendue  (It will be fun getting a consensus on this section!)

How this translates into requirements:
       	  Astrometric and photometric precision needed. 
	  Field of view
	  Depth of photometry
	  PSF FWHM, wings, uniformity
	  Photometricity of site
	  Data products necessary to carry out the science
	  Auxiliary data needed. 
	  Etc., etc. 	  

Major concerns, work for the future: 
        Models for astrometric and photometric calibration.
	Software, software, software!  Especially database issues;
	  stitching all these data together, making it available to the
	  astronomical community.  What needs to be made available in
	  quasi-real time (for synoptic science), and which as a
	  longer lead time? 
	(This report should not address technical concerns about the
	hardware, except to point out requirements, on such things as:
	   -Nature of site (fraction of photometric nights, location
	    relative to ecliptic and Galactic plane, seeing; a
	    distributed site?). 
	   -Slew rate and settling time.
	   -Field of view. 
	   -Filter choice and change rate
	   -Dynamic range needed (i.e., at what magnitude will we saturate?)
         )


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