dark energy and the lsst
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Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
12010 DOE Site Visit
Dark Energy and the LSSTChristopher Stubbs John Oliver Peter DohertyNathan FeltMeghna KundoorGautham NarayanAmali Vaz
DOE Site VisitSept 20, 2010
Harvard University Laboratory for Particle Physics and Cosmology
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
22010 DOE Site Visit
Introduction to the Dark Energy Crisis, and LSST
LSST Camera electronics development
LSST Detector testing and optimization
Improved Precision for Dark Energy Characterization
Addressing the Challenges of LSST Exploitation
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
32010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
42010 DOE Site Visit
Emergence of a Standard Cosmology
Our geometrically flat Universe started in a hot big bang Our geometrically flat Universe started in a hot big bang 13.7 billion yrs ago. It has been expanding ever since.13.7 billion yrs ago. It has been expanding ever since.
The evolution of the Universe is increasingly dominated by The evolution of the Universe is increasingly dominated by the phenomenology of the vacuum, the “Dark Energy”. the phenomenology of the vacuum, the “Dark Energy”.
““Dark matter”: what is it? Dark matter”: what is it?
Ordinary matter is a minor component.Ordinary matter is a minor component.
Luminous matter comprises a Luminous matter comprises a veryvery small fraction of the mass of the small fraction of the mass of the Universe. Universe.
preposterouspreposterous
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
52010 DOE Site Visit
Large Synoptic Survey TelescopeTop ranked ground-based project in 2010 Decadal SurveyTop ranked ground-based project in 2010 Decadal Survey
Optimized for time domainOptimized for time domain
scan modescan mode
deep modedeep mode
10 square degree field10 square degree field
6.5m effective aperture6.5m effective aperture
24th mag in 20 sec24th mag in 20 sec
>20 Tbyte/night>20 Tbyte/night
Real-time analysisReal-time analysis
Engineered to minimize systematics for Dark EnergyEngineered to minimize systematics for Dark Energy
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
62010 DOE Site Visit
• Stubbs has long-standing engagement and leadership role in LSST:– Past member of LSST Board of Directors– Original LSST Project Scientist– Current member of LSST Science Council– Coordinator for DOE efforts on SN cosmology– Likely head of system commissioning team– Co-author on LSST Science Book– Laid intellectual foundation for calibration scheme
– Adopted by LSST, by Dark Energy Survey… and others
Our efforts on LSST…
And the 12 ft diameter LSST secondary mirror is sitting in our lab…
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
72010 DOE Site Visit
LSST Camera system: – electronics development, – back end modules
LSST Detector Test and Characterization: – Detector test system is here– Responsibility for device testing and optimization
LSST Calibration system:– Conceptual development and refinement– Laboratory development of projector system– Same philosophy being adopted for DES.
Preparing for LSST Data Analysis:– Optimal data reduction techniques and analysis– Supernova observations as a probe of dark energy– Minimizing system uncertainty budget for supernova cosmo.
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
82010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
92010 DOE Site Visit
Cryostat Assembly21 “Science Rafts” 4 special purpose
“Corner Rafts” for guiding and
wavefront sensing 16 Mpixel CCD image sensors
~3.2 Gpixels total
LSST Focal Plane Overview
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
102010 DOE Site Visit
Large focal plane ~ 3.2 GPixels Rapid exposures back to back 15 second (cosmic ray rejection) Low dead time 2 second readout Low read noise 6 e rms (limited by sky shot noise) Read time and noise specs can only be met by highly segmented sensors and highly parallel readout.
1 readout channel per megapixel 3,200 readout channels
High density ASIC based readout system “a la hep”.
Requirements
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
112010 DOE Site Visit
9 Sensor Raft – 144 Readout channels
Raft
FEE
BEEHarvard
Deliverable
Raft Tower Assembly
Electronics must live in “shadow” of raft
• 6 Back End Boards• 24x 18 bit video ADCs/Board• “Slo-controls”, thermal control, etc
• 1 “Raft Control Module”• Readout state machine (sequencer)• Data collection + fiber optic to DAQ• Slow control processing
LSST Raft Tower Electronics
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
122010 DOE Site Visit
Back End Electronics – Harvard deliverable Status• All boards in 2nd or greater version• Current version supports 144 readout channels, fiber optics, etc. • Under test – ADC performance measured• Integration with FEE and DAQ Ongoing• Raft Control Crate fully designed. Multiple copies will be made available for testing in collaboration. • Firmware development continuing for BEB & RCM
Full system status• 2nd generation ASICs tested • 3rd and final generations in design• 2nd generation FEB completed. Under test. U. Penn• 2nd generation BEB under test in Raft Control Crate – Harvard• Vertical Slice testing – In progress, will continue through CD1 and beyond• Additional Raft Control Crates under construction for collaboration use
LSST Electronics Status
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
132010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
142010 DOE Site Visit
LSST Detector Test Overview• Multiple Test Facilities (BNL, LPPC, etc.)• Multiple Detector Vendors (E2V, ITL, others?)• Stringent Requirements (flatness, PSF, QE)• Comprehensive Testing and Characterization• Repeatability, Reproducibility, Consistency• 189 Sensors in LSST Focal Plane!• Led By Paul O’Connor (BNL)
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
152010 DOE Site Visit
LSST Detector Testing at LPPCCurrent LPPC Efforts :
– Detector Test Stand Hardware Management– Preparation and Validation of Test Hardware– Electro-Optical Testing of Candidate Detectors– Development of Test Software– Establishing Detector Test Standards
LPPC Strengths:Decades of Experience in CCD Image Sensor Test
A Rapidly Growing Role for LPPC in LSST Detector Test
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
162010 DOE Site Visit
Detector Test Stand Hardware Management
Managing the acquisition and distribution of detector test electronics to all test sites:
Brookhaven National LaboratoryHarvard LPPCL'Institut National de Physique Nucléaire
et de Physique des Particules (IN2P3) SLAC/UC DavisPurdue University
Managing the Standardization of Test Facilities
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
172010 DOE Site Visit
Validation of Test Hardware
Currently finishing assembly and validation of BNL cryostat for testing E2V candidate sensors in Oct/Nov 2010 timeframe
Preparing for integration and test of ITL candidate sensors at LPPC in Nov/Dec 2010 timeframe
Working with IN2P3 to finalize detector test facility in Paris
Coordinating development of a new test facility at Institute of Physics, Academy of Sciences, Prague
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
182010 DOE Site Visit
Electro-Optical Testing of Candidate DetectorsLPPC has a long-established detector test facility
that has been used on multiple projects: PISCO, Pan-STARRS, LSST, etc.
LPPC is constructing a new detector test facility specifically for LSST image sensors (lab space courtesy of Dr. Franklin)
LPPC has more experience in the testing of CCD image sensors than any other institution in the LSST collaboration
Working in close collaboration with LSST partner institutions to support device testing at multiple locations
STA/ITL Prototype Imager
E2V Prototype Imager
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
192010 DOE Site Visit
Development of Detector Test SoftwareMultiple test facilities require the ability to reduce image data with consistent
results
Currently multiple sites use diverse software toolsets– Good for development phase (diverse ideas, techniques, etc)– Bad for the long term (consistency, coherence, etc)
LPPC will assist existing developers to standardize on a set of software tools for use across the collaboration
LPPC will draw on tools in use both at LSST partner sites, industry standard tools, and its own extensive library of CCD test data reduction code
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
202010 DOE Site Visit
Establishing Detector Test StandardsLPPC is• Leading the effort to standardize the image data set required
for device characterization• Working to formalize image header keywords for consistency
across facilities• Coordinating the effort to standardize the software tools used
to reduce detector test data• Helping create a standard detector test report for use at all
facilities engaged in LSST image sensor testing
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
212010 DOE Site Visit
Near-Term LPPC Detector Test Goals
• Delivery of detector test cryostat to BNL for E2V detector test (10/2010)• Characterization and optimization of ITL detector prior to NSF PDR and
DOE CD-1 (11-12/2010)• Completion of new test facility (12/2010)• Definition of standardized image file header keywords (12/2010)• Preparing to integrate detector test and Raft Tower Electronics for
‘Vertical Slice Test’
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
222010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
232010 DOE Site Visit
Passbands and System Sensitivity
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
242010 DOE Site Visit
Pushing to Better Precision• LSST promises considerable advances over current capabilities
• The requisite flux precision for pushing to the next level of characterization of the Dark Energy is < 1%
• Supernova distance measurements• Photometric redshifts for weak lensing measurements, and BAO analysis.
• Inadequate corrections for variable atmospheric transmission will be a leading source of systematic error.
• SDSS achieved few-percent precision all-sky, while differential measurements in single frames reach part per thousand levels
• We are nowhere close to the Poisson limits for objects with SNR > 100.
Why?
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
252010 DOE Site Visit
Broadband photometry
Four aspects to the photometry calibration challenge: 1. Relative instrumental throughput calibration (i.e. get the flux ratios right)2. Absolute instrumental calibration (This is far less important)3. Determination of atmospheric transmission4. Determination of Galactic extinction (most stars lie behind the extinction layers).
Historical approach has been to use spectrophotometric sources (known S()) to deduce the instrumental and atmospheric transmission, but this (on its own) is problematic: integral constraints are inadequate, plus we don’t know the sources well enough.
φ(i, j) = S(λ )A(λ )G(λ )T(λ ) dλ∫sources∑
Source Atmosphere Instrumental transmissionSource Atmosphere Instrumental transmission
Galactic scatteringGalactic scattering
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
262010 DOE Site Visit
Our Basic Philosophy for LSST Calibration1. Use precisely calibrated NIST photodiodes as the fundamental
metrology basis for flux measurements.
2. Measure instrumental throughput relative to known photodiode.
3. Measure atmospheric transmission function directly.
4. Deliver, for each photometric measurement, the effective passband through which it was obtained.
Stubbs & Tonry, ApJ 646, 1436 (2006)
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
272010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
282010 DOE Site Visit Stubbs et al., ApJ in press
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
292010 DOE Site Visit
LSST Calibration Screen Optics - Ms. Amali Vaz
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
302010 DOE Site Visit
Accelerometers on LSST calibration telescope
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
312010 DOE Site Visit
Atmospheric Transmission
Stubbs et al., PASP 119, 1163, 2007.
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
322010 DOE Site Visit
So we need to measure (or determine)1. Extinction due to clouds, and transparency variations: This can be
bootstrapped if a given field is observed many times, some in cloud-free conditions. Tougher if only a few visits per band.
2. Aerosols: time variable and tough to measure well.
3. Water vapor: differential photometry or spectroscopy, or precise dual-band GPS?
4. Barometric pressure, for MODTRAN input.
Similar challenges for cosmic ray experiments: Auger, Veritas, et
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
332010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
342010 DOE Site Visit
Differential Narrowband Water Monitor• Simultaneous measurements on-band (940 nm) and off-band (880
nm) using stars to back-light atmosphere.• Proof-of-principle data shows promising results
940 nm940 nm
880 nm880 nm
300 mm f/2.8 1K x 1K deep 300 mm f/2.8 1K x 1K deep depletion CCDdepletion CCD
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
352010 DOE Site Visit
Dual-band Geodetic-Quality GPS Water vapor in
atmosphere produces difference in arrival times for GPS signals at two different wavelengths
(1.575 and 1.228 GHz).
http://www.gpsworld.com/files/gpsworld/nodes/2002/721/chart3.jpg
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
362010 DOE Site Visit
A universal observed stellar locus • Disk M dwarfs with metallicity [Fe/H] > 0.7 all from closer than ~1 kpc so minimal sensitivity to metallicity gradients
• Main sequence disk stars and evolved halo stars
High et al., AJ 138, 110, 2009
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
372010 DOE Site Visit
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
382010 DOE Site Visit
Refining supernova light curve analysis:
LSST won’t have supernova spectroscopy
Host extinctionredshift extractionIb, Ic contamination…
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
392010 DOE Site Visit
Is the accelerating expansion the same in different directions? A. Diercks’ PhD thesis, UCSB, 1999Cook & Lynden-Bell, MNRAS 401, 1409 (2009), and references therein
Harvard UniversityDepartment of PhysicsLaboratory for Particle Physics and Cosmology
402010 DOE Site Visit
LSST: Plans for FY2011• Camera electronics engineering• Detector device testing and characterization• Continue to refine and test innovative
calibration methods• Establish SN dark energy working group, with
LBL and Fermilab, refine light curve fitting• Develop instrument calibration and atmospheric
monitoring apparatus.
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