Transcript may stars be the actors and dark energy direct shoot a movie in the sky Chihway Chang Oct.8 ‘2008

may stars be the actors and dark energy direct
shoot a movie in the sky
Chihway Chang Oct.8 ‘2008
outline
• Why LSST ?
• Science goal and science driven design
• The project system
– Telescope
– Camera
– Data management
• Focal plane problem & weak lensing
• Conclusion
The reason
• What is missing in the astronomy society?
– Traditional operation of telescopes
– Public data available for all science use
– “It will not be possible to answer the great questions in
astronomy and cosmology without a technological
breakthrough. we need something that goes wider,
deeper, and faster than any instrument we have today.” -Anthony Tyson (UCD)
– Large Synoptic Survey Telescope — let’s shoot a movie
in the sky
Cast
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~10 billion galaxies +10 billion stars with redshift
~1 million gravitational lenses
~10,000 asteroids
~1 million supernovae
Gamma ray bursts
New phenomena
 Large and complete 3D sky map
The science goal
• Probing dark energy & dark matter
– Weak lensing on galaxies (WL)
– Baryon acoustic oscillation (BAO)
– Type Ia Supernovae
• Taking an inventory of the solar system
– Near-Earth objects (NEO) survey
• Exploring the transient optical sky
– Active galactic nuclei (AGN)
• Mapping the Milky Way
– Galaxy formation and evolution
Science-driven
instrumentation
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Single visit depth : NEO, variable objects
Total visit depth: extragalatic / galatic
PSF, image quality: WL
Single visit exposure time: moving objects,
atmosphere, readout noise
• Filter components: photometric z
Crew
• Telescope
– Telescope optical and mechanical design,
calibration, building and site
• Camera
– Electronics, filter, shutter, cryostat, controller,
guider, detectors, simulation and calibration
• Data management
– Image processing pipeline, data storing and
public access
Telescope basics
• 9.6 degree2 field of view
(Keck ~ 0.2)
• Etendue =
collecting area * sky coverage
~ 320 m2 degree2
(Keck ~ 4)
• Three mirror Paul-Baker:
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M1 8.4 m primary
M2 3.4 m convex secondary
M3 5.0 m tertiary (monolithic design)
L1 L2 L3 (refractive corrector)
• University of Arizona's Steward Observatory Mirror Lab
Too much data!
• (4 byte per pixel) * (32 billion pixels per exposure)
* (continuous 15 or 1 sec exposures) ~ 1.6 GB/sec
• One pass ~ 20,000 square degrees ~ three nights of
observation ~ 150 TB
• Overtime ~ 31,000 square degrees ~ 5 years of
observation ~ 30 PB (whole sky ~ 41,253 degree2 )
No big deal…
Challenge
• Technology:
high data rate, real-time analysis, later data
exploration
• Computational cost:
PB disk storage system  $1 million
in five years, this price should drop to well
below $100,000
• National Virtual Observatory
A man-size camera
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1.6 * 1.6 * 3 m3, 2800 kg
(64 cm)2 flat focal plane with 3.2G pixels
Focal plane operate at -100 degree C
Six 75cm filters UVBRIY
Filters
• 5 band from SDSS ugriz + y
• Photometric redshift: linear regression fitting
of spectral energy distribution (SED)
templates
• Y band: designed
to probe high z
objects
Photometric redshift
By Anthony Tyson
Cryostat and
contamination test
Focal plane
Focal plane flatness
and weak lensing
Dark energy and
dark matter
• The visible mass and known matter cannot
explain the why the Universe behaves
• How to “see” DM:
– rotational speeds of galaxies
– orbital velocities of galaxies in clusters
– gravitational lensing
• How to “see” DE:
– baryon acoustic oscillation
– SN
Weak lensing basics
• Gravity bends light
• Map of dark matter
• Method:
– Use stars to construct PSF map
– Deconvolve galaxy with this PSF map
– Measure residual ellipticity to infer shear
• Lensing signals are typically WEAK
• Accurate “shape” measurement is crucial
• The misalignment of the optics can easily distort image
shape and mimic shear
• LSST may have more difficulties because the focal plane is
enormous
10 um defocus
The simulator
• John Peterson @ Purdue
• Include science:
– Kolmogorov density screen generator multi-layer frozen
screen atmosphere
– ray-tracing refraction and reflection of mirrors and
lensing
– Zernike distortions on mirror surfaces
– 6 degree of freedom motions for the optical elements
refraction
– photo-electron conversion and diffusion in silicon
– charge saturation and blooming
Basic checks
• Optics
• Background
• PSF changes
Build in
• Potato chip shapes
• Characterize and analyze PSF
0
102
-2
100
98
90
100
96
110
94
Where is this going?
• Removing instrument signature from weak
lensing data
• Understand the limit of weak lensing using
LSST
• Set specs on CCD manufacture
Conclusion
• LSST is based on the concept of “fast, wide, deep”
as opposed to traditional astrophysics projects.
• The instrumentation of LSST require high
technology and complete understanding of the
physics involved.
• Good instrumentation makes doing science easier.
• The data of LSST will be available on line to
anyone who is interested in it.
• 2014 – Let the movie begin…
Reference
• http://discovermagazine.com/2008/may/13-moviecamera-to-the-stars
• http://www.lsst.org/lsst_home.shtml (LSST official
website)
• LSST: FROM SCIENCE DRIVERS TO REFERENCE
DESIGN AND ANTICIPATED DATA PRODUCTS
(LSST overview paper)
THANKS