Subject: Putting the LSST DRM document together; input from SWG needed!

From: Michael Strauss

Submitted: Tue, 16 Sep 2003 15:18:12 -0400

Message number: 171 (previous: 170, next: 172 up: Index)

Hello all,
This is a long message, but I would like the SWG members to read it
carefully; I ask a number of specific questions for which I need
responses.

I am working on stitching together the various contributions I've
received thus far into a single document, a Design Reference Mission,
for the LSST. Please see
http://astro.princeton.edu/~dss/LSST/lsst-general/msg.131.html for the
outline from which I am working. I received no comments from all of
you on this outline, so I am sticking with it. What exists currently
(47 pages long!) is far from a first draft, and includes things that
people have sent me that they explicitly indicated were not final; I
apologize for that. Anyone who wants to dive in can find it all at:
ftp://astro.princeton.edu/strauss/LSST
It is all written in LaTeX (sorry, Al!); the main file is DRM.tex,
with each section separated out as a separate file. With the
exception of Zeljko, no-one has sent me any figures; the document
looks rather dull without them.

Again, this is not even a real first draft; it is too early, for
example, to point out typos. But it is not too early to point out
redundancies, missing sections, and wildly incorrect or impolitic
statements.

I would dearly like to have close to final versions of each section
done two weeks from today (September 30); if that seems a short time,
please remember that I first called for contributions from people at
the Tucson meeting in March... Once these are in place, we can all
look over the full document, beat it into a form we're happy with, and
submit it.

Here I describe what stage each section of the document is in at the
moment, and ask for feedback on all of it, and volunteers to write
missing sections or modify existing sections. If I had my act together,
I would put all this under CVS; without that at the moment, I will ask
anyone who wants to modify what already exists to pick up the current
draft at the anonymous ftp site above, and let me know which section
you're working on.

Introduction: Written by me. This summarizes the scientific and
technological developments that have made deep wide-field imaging such
a hot topic, and describes the three decadal surveys that call for the
LSST. It briefly lists the main science drivers which will be covered
in the document, and emphasizes that this document is non-partisan in
the single-aperture vs. distributed aperture debate.

************************************************************************
Science Justification: This is the largest section of the document,
of course. After brief generic remarks, it consists of the
following:

************************************************************************
-Potentially hazardous asteroids. Al Harris has sent me a good
first draft, but it needs further fleshing out. In particular, it
needs:
-Further discussion of the risks, including a version of the
figure showing the averaged deaths per year as a function of size
of the impactor.
-Some further discussion of the controversy of the dangers of
tsunamis, run-up and all that.
-Given that the document does not explore the full question of
optimal cadence for the survey, there needs to be a paragraph or
two describing the work that Harris and Bowell have done to date,
and what remains to be done to make this work definitive.
-There needs to be something about requirements on the
telescope/data/etc.
We should also consider writing at least a brief response to the
conclusion of the NASA committee that a large etendue is not
really needed for this job. I've asked Zeljko to think about
this.

************************************************************************
-Kuiper Belt Objects. This has been written by Gary Bernstein,
(http://astro.princeton.edu/~dss/LSST/lsst-general/msg.167.html)
with input from a variety of you. This is in very good shape;
the main thing it needs is some graphics to spiff it up a bit.

************************************************************************
-The variable universe. I have contributions from Fiona
Harrison, Mike Shara, and Zeljko Ivezic; I am currently trying to
merge the three. Fiona indicated to me that she plans further
modifications of what she sent me, so I am waiting for that. My
plan was to use Fiona's section serve as a generic introduction
to the discussion of what LSST could do for variability studies,
incorporating Zeljko's writeup of the current state-of-the-art.
I would then use Mike's discussion of using classical novae as a
specific example of scientific return from variability studies.

************************************************************************
-Galactic and Stellar astronomy. Here I am working from the
writeup that Dave Monet, Dennis Zaritsky, and Knut Olsen have
produced
(http://astro.princeton.edu/~dss/LSST/lsst-general/msg.154.html).
This needs some work in setting context; in particular, some
introductory words need to be in place about the astrometric
abilities of LSST, on which much of the science discussion
rests. I.e., how good are we actually going to be able to
measure proper motions? Parallaxes?
I also plan to incorporate some of the galactic astronomy stuff
that Zeljko has written.

Here are some specific questions, which perhaps one of the
authors of this section could address:
End of Section A.1, there is a sentence I simply don't
understand, or is out of context; I am currently planning to
drop it(but maybe it is saying something important and should be included):
"Even with SDSS, the structures that are being
found are the ones we can point to the overheads..."

Section A.2.1 makes reference to the full 3-D velocities of
stars in the local neighborhood. LSST is not going to measure
radial velocities, so this sounds like something we will not be
able to do.

Section A.2.3, another sentence I simply don't understand:
" The ambiguities in the interpretation that can be
introduced deviating from a standard halo can be seen in
the study by Geza, Evans, & Gates (1998)."

Section B.1: "LSST offers the opportunity to measure the
parallax of every object in its field of view... LSST will... measure
the positions for an estimated 1e10 stars several times per year, and
the pipeline will produce measurements and uncertainty estimators for
the position, parallax, and proper motion of every star it observes."

This is a funny way to say it; only a tiny fraction of the stars
LSST sees will have a parallax measurably different from zero;
that should be made clear. The comparison in this paragraph to
the state of art *before* Hipparchos is also a bit strange; here
we need to emphasize what we can do that Hipparchos didn't do
(i.e., go *much* fainter). In this context, somewhere we need a
discussion of GAIA, no?

************************************************************************
Supernovae. At the moment, we have *nothing* in this document
about supernovae. Peter sent me a draft rough document some time
ago, describing the use of supernovae to measure w, but it
requires very intensive spectroscopic follow-up; I am not sure how
strongly we wish to advocate this. At the March meeting, there
was an informal consensus that most of the "obvious" SN science
would be mostly done by on-going projects before the end of the
decade. It was suggested that discovery of supernovae being
strongly gravitationally lensed is something LSST could do very
well (these objects being rare enough that only a survey with a
huge etendue could find them); this needs a writeup. My
suggestion for the moment is that we not make this a main driver,
but include it in the concluding subsection of the science
justification, "Other Science LSST will accomplish." Please give
me your feedback on this.

************************************************************************
Weak lensing. Daniel and Tony have written a first draft, which
at the moment is very qualitative. I believe they are actively
working on fleshing this out. Tony has written extensively on the
drivers weak lensing puts on LSST optics,
etc. (http://astro.princeton.edu/~dss/LSST/lsst-general/msg.24.html,
http://astro.princeton.edu/~dss/LSST/lsst-general/msg.46.html
)

Tony, are you willing to put your thoughts on this matter into a
form appropriate for the present document? And Tony and Daniel,
what is the next stage in putting some numbers and equations into
the writeup?

************************************************************************
"Everything else". I intend to write a brief description of some
of the other science that LSST may be able to accomplish. The
emphasis here is that LSST data will have use for a huge range of
different scientific goals, many (most?) of which we can't
anticipate at this point. I will therefore restrict myself to a
few examples:
-Main-belt asteroid studies.
-Complete samples of quasars from variability
-Cross-correlation of ISW
-Strong lensing and clusters of galaxies
-LSST and large-scale structure at high redshift
(Further suggestions and, even better, contributed paragraphs
are most welcome!).

************************************************************************
Discussion of how this all fits together:
Discussion of cadences (already written by Zeljko)
Discussion of the distinction between studies of the static and
variable sky
Discussion of filters (Andy, your thoughts on this would be most valuable)
Except for Zeljko's contribution, none of this is written. I will
take a first stab at it.

************************************************************************
A summary of requirements on the telescope system. At the moment,
there is, or will be, a discussion of requirements that each of the
science drivers ask for as part of the discussion of the science
itself, so I intend this section to be a brief summary.
I will write this.

************************************************************************
Concerns: This will again be brief: a list of the issues we didn't
discuss (or come to a proper conclusion on), and the issues we saw as
difficult (such as software, operational models for astrometric and
photometric calibration, and so on).

************************************************************************
Finally, there will be three appendices:

A few-page description of the monolithic-mirror concept
(DMT). Tony, we could use your article for the SPIE meeting
last year, or you could write something from scratch; your
choice.

A few-page description of the multiple-mirror concept
(Pan-STARRS). Nick, we could use your article for the SPIE meeting
last year, or you could write something from scratch; your
choice.

A list of all of us. (Already written; that was easy!).

-Michael Strauss

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