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Transcript of 1 MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014 Name of...
1MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014Name of Meeting • Location • Date - Change in Slide Master
LSST Reprocessed Co-adds of SDSS Stripe 82Yusra AlSayyad University of Washington
MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE82MARCH 17, 2014
Andrew Becker, Andrew Connolly, Željko Ivezić,Simon Krughoff,Russell Owen,(U. Washington)
Jim Bosch, Robert Lupton, Paul Price, (Princeton),Mario Jurićand the LSST Data Management Team
3MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Outline
− How do we aggregate information from multi-epoch surveys, with the goal of extracting highest S/N possible. • Detect on co-add• Measure on single-epoch exposures (forced photometry)
− Summer 2013 co-add construction details• Co-addition process• Datasets produced• Preliminary quality assessment
4MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Three ways combine info from multi-epoch surveys
1. Catalog co-add: Detect and measure on single-epoch exposures and take a weighted mean or median of the measurements.
5MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Light-curves derived from detecting on single-epoch images misses information
Time
Flux
5σ detectionlimit
MeasuredMean Flux
6MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Three ways combine info from multi-epoch surveys
1. Catalog Co-add: Detect and measure on single-epoch exposures and take a weighted mean or median of the measurements.
2. Image Co-add: Detect and measure on co-added image
Lose measurements under detection threshold
7MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Measurement on Co-adds misses information
1. Poor-seeing and bright-sky images do not increase your co-add SNR.
2. Co-add PSFs are hard to characterize. 3. Impossible to distinguish between galaxies and high proper
motion stars.
PSF 3P
SF
2Psf 1
Image 2Image 1 Image 3COADD
Lang+ 09
Individual exposures: objects are undetected or marginally detected
Moving point-source and galaxy models are indistinguishable on the coadd
Solved by PSF-Matching: (Kaiser 04) (Huff+11)
8MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Three ways combine info from multi-epoch surveys
1. Catalog Co-add: Detect and measure on single-epoch images and take a weighted mean or median of the measurements.
2. Image Co-add: Detect and measure on co-added image
3. Detect on co-added image. Measure on single-epoch exposures.
Misses measurements under detection threshold
Requires PSF-matching. Can’t characterize objects.
9MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Summer 2013 Stripe 82 Co-addition
10MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Summer 2013 Stripe 82 Co-add Process
ucoadd
gcoadd
rcoadd
icoadd
zcoadd
Catalog
catalog
catalog
catalog40M rows
catalog
Detect and Measure
Detect and Measure
Detect and Measure
Detect and Measure
Detect and Measure
Detect and Measure with: • StackFit/CoaddPSF• Deblender• 3σ detection threshold
• Measure flux at positions in i-band co-added catalog
Details next
Forced Photometry
Catalog15 B rows
~80 epochs per band
Force photometry at positions
11MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Steps to make a deep co-add
− Define the co-add projection and geometry
For each run:1. Resample to defined output geometry2. Scale to co-add zeropoint
12MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
2. Scale to a co-add zeropoint
− Zeropoint varies spatially and temporally
− Photometric self-calibration calculated before co-adds are generated
− Used 1-D model of zeropoint (per camcol) as multiplicative scale factor. Figure: Realization of a 0.5 mag cloud based on a structure
function of observed clouds and some realistic assumptions about cloud-size and velocity. (image credit: Lynne Jones)
RA & time
Dec
13MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Steps to make a deep co-add
− Define the co-add projection and geometry
For each run:1. Resample to defined output geometry2. Scale to co-add zeropoint 3. Match sky-levels/backgrounds
14MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Background-subtracted coadd Single-epoch visit
5 arcmin
15MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Background-subtracted coadd Background-matched coadd
5 arcmin
16MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
3. Match Backgrounds
− Goal: Estimate the difference in sky level between successive runs• Leave in common-mode (astrophysical) background
- Wings of galaxies, diffuse nebulosity • Remove time-dependent backgrounds
- Atmospheric: changes in sky, airglow, scattered moonlight
− One realization of the sky survives, but we can subtract this at higher S/N
− (see Huff+ 11)
17MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
3. Match Backgrounds
− Start with a reference image. • Locks the sky-level of a co-add patch to
that of its neighbors• Ensures the co-add will be seamless at
patch boundaries• Use a run with low background variation
as a reference image
Reference Image for example patch
20MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Steps to make a deep co-add
− Define the coadd projection and geometry
For each run:1. Resample to defined output geometry2. Scale to co-add zeropoint 3. Match sky-levels/backgrounds
For ensemble of resampled & scaled visits:4. Stack co-add
- Weight whole image by inverse variance and stack with 5σ-clipped mean for eliminating:• moving objects, transients, satellite trails• Small-scale instrumental: glints
Figure: 5 sq. deg. background-matched coadd composite
(g,r,i)~55 epochs
Region: AqrGalactic lat = -35.0
Figure: 5 sq. deg. background-matched coadd composite
(g,r,i)~55 epochs
Region: AqrGalactic lat = -35.0
23MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Summer 2013 Stripe 82 Co-add Process
ucoadd
gcoadd
rcoadd
icoadd
zcoadd
Catalog
catalog
catalog
catalog40M rows
catalog
Detect and Measure
Detect and Measure
Detect and Measure
Detect and Measure
Detect and Measure
Detect and Measure with: • StackFit/CoaddPSF• Deblender• 3σ detection threshold
• Measure flux at positions in i-band co-added catalog
Details next
Forced Photometry
Catalog15 B rows
~80 epochs per band
Force photometry at positions
24MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Preliminary Quality Assessment
25MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Median zeropoint is stable
W
X
Zeropoints calibrated using the Ivezic+ 07 star catalog. (See talk on Wednesday)
Ivezic+04
Point sources
26MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
RMS approaches intrinsic width of w ~ 0.01
r mag
Median PSF flux in epochs
27MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Forced phot. adds 0.5 mag to SNR=5 depth
28MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
29MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Dataset is publicly available. Access?
− What’s available?• 5 sq. degree region is indexed and ready to use today.• 235 sq. degree region from previous data challenge available
- g,r,i, no deblending, forced photometry seeded on r-band
− How to access? • LSST Science Collaboration members can request a mysql account and
explore the databases hosted at NCSA• Send me a list of positions (< 10M rows) and I’ll send you an ascii or fits
file with forced photometry and aggregates
− Code is open source. − Caveat (prototype code):
• No forced galaxy photometry. • Deblender not dependable in blends containing stars < 17mag.
30MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Summary
− Stripe 82 has proved to be a great dataset for testing LSST software.
− Result of Summer 2013 production run is deeper than best publicly-available optical Stripe82 catalog.
− Forced Photometry:• Complete light curves for even marginally detected objects • Disentangles extended and moving sources • Includes all epochs (not just the best seeing, lowest background)
31MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
32MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Appendix
34MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
i-band Completeness
35MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Completeness
HST SDSS
36MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
Star galaxy separation
37MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
False galaxies are unresolved blends
38MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
CORE DATA PROCESSING SOFTWARE PLAN REVIEW | SEATTLE, WA | SEPTEMBER 19-20, 2013
False stars are compact
39MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Winter 2013 comparison to previous coadd
We go deeper than Annis et al. (2012) by 0.75 magnitudes at same
equivalent S/N.
SNR
100
10
24 25
40MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 201440
Quasar Luminosity Function at z ~ 4
41MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
42MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Level 2 Data Processing
Data Products Definitions DocumentSection 5.2
43MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
3. Background Matching
− For N input images, find least sq. solution of all N(N-1)/2 difference images (e.g. Huff et al. 2011) (Presented as “NN2”- algorithm by Barris et al. 2009)• Offers better relative offsets in sky-levels, but does not provide an
absolute sky-level • NN2 does not eliminate need for a reference image.
- If you choose the mean you get a patchwork quilt.- If you choose zero, you lose all astrophysical background on scales greater
than a patch• We tested both NN2 and simple ref-image. Preliminary conclusion is that
the gains are not significant. • We will re-examine on the ecliptic where the reference image may be
heavily masked due to asteroids
44MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Level 2 Processing
DRP begins with processing, detection, and measurement on single frames, generating Sources.
These are used to photometrically and astrometrically calibrate the survey.
A series of coadds is built next, where Objects are detected.
Detections on co-adds are deblended and associated to form a master object list.
The objects are simultaneously characterized in all observed epochs (MultiFit).
Time variability is characterized by independent measurement of Forced Sources in individual epochs.
45MULTI-WAVELENGTH, MULTI-EPOCH HERITAGE OF STRIPE 82 | PRINCETON, NJ | MARCH 17, 2014
Types of coadds planned in LSST
Coadd Type
Subset of images Driver Bands Pre-served
Deep All suitable images Detect objects on static sky. Maintaining low surface brightness.
ugrizy + M ✔
Short Period
Binned by year Detect long-timescale or moving objects that would be washed out in full-depth coadds
ugrizy + M ✗
Best-Seeing
Only best seeing images (e.g. top quartile)
Assist deblending ugrizy ✗
PSF-matched
All suitable images Measure well-defined colors of galaxies
ugrizy ✗
Binned by seeing and airmass
Image Differencing Templates ugrizy ✔