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 ~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

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 The science goal

Science-driven instrumentation 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

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 Crew

Telescope basics 9.6 degree 2 field of view (Keck ~ 0.2) Etendue = collecting area * sky coverage ~ 320 m 2 degree 2 (Keck ~ 4) Three mirror Paul-Baker: –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 degree 2 )

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 1.6 * 1.6 * 3 m 3, 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 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

Where is this going? Removing instrument signature from weak lensing data Understand the limit of weak lensing using LSST Set specs on CCD manufacture

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 – Let the movie begin… Conclusion

Reference camera-to-the-stars (LSST official website) LSST: FROM SCIENCE DRIVERS TO REFERENCE DESIGN AND ANTICIPATED DATA PRODUCTS (LSST overview paper)

THANKS