Subject: Comments on SWG document, from Tony Tyson

From: Michael Strauss

Submitted: Wed, 9 Jun 2004 08:36:31 -0400

Message number: 213 (previous: 212, next: 214 up: Index)

Comments on LSST SWG report - T. Tyson 6/6/04

Michael,
Good job. Here are some comments, starting on page 1.


Abstract: `an array1.8m telescopes.' ->
`an array of four 1.8m telescopes.'


Introduction:

Give bands and limiting mags of SDSS.

Etendue includes effects of obscuration. My records give SDSS as 5.7 
Worth checking.

Last sentence before bullets: `Among these are (in order of increasing 
redshift):'

p3: National Academies of the Sciences -National Academy of Sciences

p4: `of order 200-250' -`of order 200-400'

[the current 8.4m LSST point design has 10 sq.deg FOV and etendue of 370]

p5: 5 sigma? Better to go with 10 sigma.


PHAs:

We should check with Al Harris, but I think he said at the science 
requirements meeting that the sharp break at 1.2km has gone away

p12: Table 1. For what FWHM PSF and airmass and moon? 10 sigma better.
Photometry with 5 sigma is ratty.

KBOs:
p21: missing Bernstein etal. 2003 reference.


Variable Universe:
p23: relative to QUEST, LSST will also have far better delivered PSF


Stellar populations:

p31: re QSOs found by color, discovery by fluctuation is less prone to 
contamination.

p36: Bullock, etal 2001 reference missing


Gravitational lensing:

p45, 2nd paragraph in section 7.4:
`reduce systematic errors by 10-100' ->
`reduce systematic errors by 3-10'

p46, 2nd parag in sec 7.4.1:
add: `The mean FWHM of galaxies as a function of redshift is larger than 
0.6 arcsec. A large telescope aperture enables low surface brightness, a 
requirement for

resolving high redshift galaxies.'

p46, 3rd parag in sec 7.4.2:
`20 galaxies per arcmin^2' -`35 galaxies per arcmin^2'

p47, omit last sentence in sec 7.4.3 and join previous sentence to 
preceding paragraph.

p51, 2nd parag in sec 7.6:
`75medium' [missing words here] should be:
`At leat 75\% of the time is to be used for large scale surveys. They 
envisage deep, medium, and wide surveys (probably carried out in time of 
poorest seeing) each

addressing different science goals.'


Supernovae:

p54, sec 8.1.1, 1st parag:
`three or filters' -`three or four filters'

p55, sec 8.1.2:
could someone please explain what the last sentence means?

Sec 8.1.3, 2nd parag:
`where it is known that the cosmic where star formation' words missing

p56, sec 8.2: 8-meter -8-10 meter

p61, last sentence: dark matter -dark energy


Other science:

p65, sec 9.3, 1st sentence:
`hundreds of millions' -`billions'
(a little over 3 billion actually)

Multiplex:

p67, sec 10, last parag:
`in the considering' -`in considering'

p68, last parag: after 1st sentence, add;
`This is made much easier if the etendue is above 300'

What lies ahead:

p69, sec 11, photometric calibration:
add last comment:
`A fresh approach to precision calibration is needed.'

General comment re photometric and astromentric calibration:
`Overlapping fields and revisit dithering will help significantly in 
tying together photometric and astrometric transfer.'

p71: add after 4th bullet:
`Warping onto standard projection'

7th bullet: `these information' -`this information'


A Possible Universal Cadence:

p75, sec A5, 3rd parag:
`LSST exposure time calculator developed by A. Saha (http: ..).' ->
`LSST operations simulator developed by A. Saha.'


8.4m LSST System Reference Design:

I think I sent you a plot of 80% encircled energy vs field angle and filter.
Do you want it again?

I’m not sure how to handle this: the project has settled on a 3.5 deg FOV
(10 sq.deg) baseline design with etendue of 370. Maybe just say so at 
the end.
The reason is that a design with excellent imaging was achieved with 
moderate increase in aspericity, and the science drivers push us up 
above 300.

p84, Fig 28, `8.4-m 8.4m' -`8.4m'

add to end of figure caption:
`The 8.4m LSST design with etendue 260 was used in this simulation. A 
ten square degree design with etendue 370 is the current baseline design.'



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