Membership of the Lsst Science Working Group

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Membership of the Lsst Science Working Group

The LSST Science Working Group was convened by Jeremy Mould, Director of the National Optical Astronomy Observatory. The membership of the group is as follows, together with their principal areas of scientific and technical expertise.

Gary Bernstein, University of Pennsylvania, (weak lensing, KBOs, wide-field imaging)

Andy Connolly, University of Pittsburgh, (Photometric redshifts, galaxy clustering, data systems)

Kem Cook, Lawrence Livermore National Laboratory, (wide-field imaging; microlensing)

Daniel Eisenstein, University of Arizona, (galaxy evolution, cosmology, photometric calibration)

Peter Garnavich, University of Notre Dame, (supernovae)

Alan Harris, Space Science Institute, (NEOs and asteroid science)

Fiona Harrison, California Institute of Technology, (the variable sky)

Zeljko Ivezić, Princeton University/University of Washington, (asteroids, surveys, image processing, Galactic structure, the variable Universe)

Dave Jewitt, University of Hawaii, (KBOs and asteroid science)

Nick Kaiser, University of Hawaii, (weak lensing, cosmology, wide-field imaging, image processing, Pan-STARRS Project Scientist)

Steve Larson, University of Arizona/Lunar and Planetary Lab, (asteroid science)

Dave Monet, U.S. Naval Observatory/Flagstaff, (stellar science; astrometry)

David Morrison, NASA Ames, (NEOs and asteroid science)

Mike Shara, American Museum of Natural History, (stellar science, the variable Universe, public outreach)

Alan Stern, Southwest Research Institute, (KBOs, solar system science)

Michael Strauss (Chair), Princeton University, (quasars, large-scale structure, surveys)

Chris Stubbs, Harvard University, Stubbs@Physics.Harvard.Edu (weak lensing, wide-field imagers, supernovae and variable objects, data processing)

Tony Tyson, University of California, Davis, (weak lensing, wide-field imagers, image processing, 8.4-m LSST director)

Dennis Zaritsky, University of Arizona/Steward Observatory, (galaxy properties and photometry, wide-field imaging)

While the LSST SWG included no membership from the scientific staff of NOAO, we benefited greatly from input from a variety of people, including, but not restricted to: Sidney Wolff, Jeremy Mould, Abi Saha, Knut Olsen, Chuck Claver, Richard Green, Beatrice Müller, and Chris Smith, as well as Philip Pinto of the Department of Physics at the University of Arizona.

Towards a Design Reference Mission

for the Large Synoptic Survey Telescope (Lsst)

Report of the Science Working Group

August 2004

Table of Contents

Membership of the LSST Science Working Group i

executive summary vi

1 introduction 1

The Science Justification, 5

2 Potentially Hazardous Asteroids 6

The Impact Hazard, 6

The Hazard of Sub-kilometer Impacts, 9

Status of Current Surveys and Next Generation Goals, 11

Requirements for an Effective PHA Survey, 12

Summary of Requirements, 15

References Cited, 16

3 Kuiper Belt Objects 17

Kuiper Belt Science Goals for LSST, 17

Required Signal-to-Noise for KBO Science, 19

The “Shallow” LSST Sample, 19

A Deep KBO Survey, 21

Occultation Searches, 22

Required Technical Specifications, 23

Open Questions, 24

References Cited, 24

4 The Variable Universe: Explosive Transients,

the High Energy Sky, and Variable Stars 25

Gamma-ray Burst Afterglows: Orphans and Light Curves, 25

Binary Mergers – Gravitational Astrophysics, 26

The High-Energy Sky – Teaming with GLAST and EXIST, 27

Variability and Stellar Astrophysics, 28

LSST Requirements, 29

References Cited, 32

5 stellar populations and the structure

of the milky way 33

Introduction, 33

The Structure and Accretion History of the Milky Way, 33

Tracing the Luminous Halo, 34

Tracing the Dark Halo, 36

Inter-galactic Tramp Stars and Classical Novae, 37

A Complete Sample of Stars within 200 Parsecs, 38

Astrometry, 38

The Parallax Survey, 39

The Wiggle Survey, 39

Summary of Requirements, 40

References Cited, 42

6 Gravitational lensing, weak and strong 43

Introduction, 43

Weak Lensing and Dark Energy, 43

Cluster Counting via Weak Lens Tomography, 45

Power Spectrum and Bispectrum Tomography, 46

Shear Cosmography, 48

Accuracy of Derived Parameters, 49

Gravitational Lensing and the Nature of Dark Matter, 49

Dark Matter in Cluster Cores, 49

Galaxy-scale Dark Matter, 50

Image Quality and Weak Lensing Analyses, 51

The Effects of Seeing, 51

Targets for Systematic Error Levels, 52

Controlling Shear Systematic Error, 53

Diagnosing Systematic-Error Contamination, 53

Photometric Redshift Errors, 54

Turning Science Goals into Requirements, 54

Shear Measurement, 55

Photometric Redshifts, 55

Cluster dN/dz, 56

General Instrument Specifications, 56

Where Will WL Cosmology Be in Ten Years?, 58

Comparison of Facilities, 59

The Work Ahead, 60

References Cited, 60

7 SUPERNOVAE and the LSST 61

Moderate Redshift Type Ia Supernovae, 61

Constraining the Dark Matter Equation of State, 61

Supernovae and Gravitational Lensing, 62

The Physics of Supernovae, 63

Moderate Redshift Type II Supernovae, 63

High Redshift Supernovae, 64

Requirements, 65

References Cited, 68

8 other science topics 69

Main-belt Asteroids, 69

Quasars and Active Galactic Nuclei, 71

LSST and Large-Scale Structure, 72

References Cited, 72

9 Realizing The LSST Multi-plex Advantage 73

10 Lsst Data Access: A Recommendation 76

11 What Lies Ahead 79

Photometric Calibration, 79

Astrometric Calibration, 79

Observatory Location, 80

Exposure Time for Individual Exposures, 80

Filters and Cadences, 81

Data Systems and Data Distribution, 82

Comparing Missions, and the Scientific Landscape in 2012, 83

References Cited, 84


A A Possible Universal Cadence 87

The Constraints on Time Interval between Two Revisits, 87

A Single Night Strategy, 88

Night-to-Night Strategy, 89

Multi-band Strategy, 90

The Sampling of Different Time Scales, 90

B The 8.4-m Lsst System Reference Design 91

The 8.4-m Telescope, 91

Optical Design, 91

Telescope Design, 92

The Camera and Focal Plane Assembly, 93

Camera Design, 93

Detector Arrays, 94

8.4-m LSST Data System, 94

8.4-m LSST Data Flow, 95

8.4-m LSST Software Architecture, 96

Operations Simulations: An 8.4-m LSST Design Reference Mission, 96

C PAN-STARRS: Overview and project status 100

Pan-STARRS System Design, 100

Telescopes, 100

Detectors, 102

Fast Guiding, 102

Surveys and Operation Modes, 103

Data Pipeline, 103

Moving Object Pipeline, 104

Basic Data Products, 104

Performance Metrics, 105

Image Quality Analysis, 105

Read Noise and Read/Slew Times, 107

Collision Hazard Reduction, 107

Pan-STARRS Project History, 109

Executive Summary

Three nationally endorsed decadal surveys have stated that a high priority for U.S. planetary science, astronomy, and physics over the next decade should be a dedicated wide-field imaging telescope with an effective aperture of 6-8 meters. Such an instrument, in dedicated survey mode, could catalog 90% of the asteroids whose orbits cross that of Earth with size greater than 200-300 meters, revolutionize our understanding of the Kuiper Belt with orbits of over 105 objects beyond the orbit of Neptune, allow unprecedented mapping both of the distant Galactic halo and the local solar neighborhood, explore the optically faint variable Universe, obtain huge samples of supernovae to redshifts of unity, and yield insights into the dark energy by measuring the gravitational lens signal with high accuracy. This document expands upon this scientific case and concludes that building such a facility is indeed in the best interest of the U.S. scientific community. We briefly discuss two different approaches that have been suggested to implement this goal: a single monolithic telescope with an 8.4-m primary and a 3-3.5 field-of-view, and an array of 1.8-m telescopes, each with a large field of view and a separate imaging camera. Deciding the superiority of either approach is left for future work.

1 Introduction

Many of the dramatic advances in astronomy have come about via massive surveys of the sky in wavebands from gamma rays to radio. The ability to carry out these surveys, in turn, has been driven by technological advances: in telescope design, detector technology, and software and processing power. For decades, the state of the art in wide-field imaging in the visible part of the spectrum was the photographic Palomar Observatory Sky Survey (POSS) and its southern counterpart, which was carried out in Australia. However, with the advent of large-format CCDs and the electronics to build cameras with substantial numbers of these devices, it has been possible to build wide-field imaging cameras using these much more sensitive detectors. As of this writing, many of the 4-8 meter class telescopes around the world have CCD mosaic imaging cameras with fields of view from 20 arcminutes to over a degree, and many more are planned. Moreover, these instruments are increasingly being used for massive surveys of the sky—such as the NOAO Deep Wide Field Survey (http://www., which covers 18 deg2 in BRIJHK; the Deep Lens Survey ( ), which will cover 24 deg2 in four bands; and the planned Legacy survey on the Canada-France-Hawaii Telescope (CFHT; http://www.cfht., which will cover 1300 deg2 in three bands. In addition, smaller telescopes are being used to carry out dedicated variability surveys, such as the Optical Gravitational Lens Experiment (OGLE;, which uses a 1.3-m telescope and an imaging camera 35 arcmin on a side to obtain light curves for literally millions of stars in the Galactic Bulge and the Magellanic Clouds; and the Lincoln Near Earth Asteroid Research survey (LINEAR; which uses a pair of 1-m telescopes with 2 deg2 fields of view to search for asteroids, especially those whose orbits may take them close to the Earth.

The current state of the art survey for wide-field optical imaging is the Sloan Digital Sky Survey (SDSS;; York et al. 2000), which uses a dedicated 2.5–m telescope with a 3 diameter field of view to obtain photometry to rAB ~22.5 in five photometric bands (u,g,r,i,z). As of this writing, it has imaged roughly 7000 unique square degrees of mostly high-latitude sky in four years of operations. Its principal scientific drivers are related to the large-scale distribution of galaxies, but the scientific results that have come from these data range from studies of the colors of main-belt asteroids (Ivezić et al. 2003) to galaxy-galaxy gravitational lensing (McKay et al. 2001), to the discovery of the highest-redshift quasars (Fan et al. 2003). The lesson to take away from this is that wide-field survey data, even if focused on a specific scientific goal, will find wide applicability to a very large range of astronomical topics.

A useful measure of the surveying capability of an imager on a given telescope is its étendue, the product of the solid angle  subtended by the camera and the collecting area A of the telescope. The SDSS has an étendue of A = 5.6 m2deg2; for comparison, the wide-field Suprime-Cam on the 8-m Subaru telescope has A = 13.5 2 deg2. Such étendues, impressive though they are, are simply not adequate to address some of the most pressing scientific questions that face us. Among these, in order of characteristic distance from the Earth, are:

  • The Population of Near-Earth Asteroids

Ever since the realization in the late 1970s that the great extinction of the dinosaurs at the Cretaceous-Tertiary boundary 65 million years ago was probably caused by an asteroid or cometary impact, the dangers of future impacts have been studied intensely. There does exist a population of asteroids whose orbits take them close to Earth; a collision with one as small as one kilometer could be devastating to life on Earth, and even one as small as 200–300 meters would cause widespread death and destruction. The U.S. Congress has mandated that at least 90% of the Near-Earth Asteroids with diameters greater than one kilometer be discovered and orbits determined for them by the year 2008. It is now uncertain whether this goal will be met (Jedicke et al. 2003), even with the best efforts of surveys like LINEAR. The enhanced goal of discovering and tracking most of the asteroids above 200 meters will clearly take a telescope with much larger collecting area.

  • The Study of Kuiper Belt Objects

These are asteroids with orbits beyond that of Neptune. The first of these was discovered only a decade ago (Jewitt & Luu 1992); roughly 800 examples of this major new component of the solar system are known now. Much larger samples, which will require massive deep surveys of large areas of sky, would have much to teach us about the dynamical history of the solar system, the origins of comets, and formation mechanisms of planets.

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