dark energy and the lsst

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



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



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



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



• 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…



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.



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



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



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



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



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)



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



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



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



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



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



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



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’



Passbands and System Sensitivity



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?



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



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)


282010 DOE Site Visit Stubbs et al., ApJ in press



LSST Calibration Screen Optics - Ms. Amali Vaz



Accelerometers on LSST calibration telescope



Atmospheric Transmission

Stubbs et al., PASP 119, 1163, 2007.



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



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



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



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



Refining supernova light curve analysis:

LSST won’t have supernova spectroscopy

Host extinctionredshift extractionIb, Ic contamination…



Is the accelerating expansion the same in different directions? A. Diercks’ PhD thesis, UCSB, 1999Cook & Lynden-Bell, MNRAS 401, 1409 (2009), and references therein



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.

dark energy and the lsst

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