The Calán/Tololo Supernova Survey Mark M. Phillips Carnegie Observatories.
LSST Image Quality and Effects Seen Through the …...Cerro Tololo observations. These atmospheric...
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( ) ( ) iyy ixx iyy ixx e + − = 1 ( ) ( ) iyy ixx ixy e + = 2 2 2 2 2 1 e e e + = Ellipticity definition from 2 nd intensity moments ABSTRACT The 8.4m Large Synoptic Survey Telescope (LSST) is a new 3.5 degree field of view facility for the purpose of studying the nature of dark energy and matter along with the time varying nature of the optical universe. These science missions require precise knowledge and control of both the size and shape of the point spread function (PSF) delivered by the LSST. Here, we present analyses of three areas of image quality that are critical to the LSST: 1) the stability and angular correlation of the stellar PSF second moments as seen through a turbulent atmosphere typical of a high quality observing site and the baseline LSST optical design, 2) the ability to recover a synthetically induced gravitational shear signal on Hubble Deep Field data modified to mimic seeing and telescope aberrations, and 3) the effects of chromatic atmospheric refraction through the LSST filters on image shape and field registration. For the stability, angular correlation and chromatic refraction studies we compare our simulations with data obtained on modern new technology telescopes. LSST Image Quality and Effects Seen LSST Image Quality and Effects Seen Through the Atmosphere Through the Atmosphere C. F. Claver (NOAO), S. Asztalos (LLNL), A. Becker (U. Washington), J. G. Jernigan (LBL), S. M. Kahn, J. R. Peterson (SLAC), L. Rosenberg (LLNL), V. Margoniner (UC Davis), J. A. Tyson (UC Davis), D. Wittman (UC Davis) 1) PSF Ellipticity Angular Correlation : Turbulent OPD Point Spread Function 0.000 0.025 0.150 … … … Time (seconds) Fourier Transform ∑ = sec 10 0 t On Axis Image Off Axis Image Difference Image 10" separation 120" separation 3.2 arcsec 10 second integration E E1 E2 Ellipticity Residual versus Angular Separation -0.004 -0.002 0.000 0.002 0.004 0 20 40 60 80 100 120 140 E2 Residual Separation (arcseconds) 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0 20 40 60 80 100 120 140 E1 Residual Separation (arcseconds) 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0 20 40 60 80 100 120 140 Ellipticity Residual Separation (arcseconds) Subaru 10sec exposures show ellipticity residual amplitudes (colored points) consistent with model results (black points). Raw de-trailed PSF corrected 1 3 a r c m i n <shear> <shear> = 0.07 = 0.07 <shear> <shear> = 0.000013 = 0.000013 2) High Fidelity Simulation Development 3) Ellipticity from Atmospheric Refraction Synthetic Galaxies Cosmology (108.14, .15, .16, .17, .18, .20, .27) Atmosphere Validate atmosphere Camera (poster 108.05) Control system Operations Simulator (poster 108.09) Synthetic data set Telescope (poster 108.04) Modeling Process Flow Atmosphere Model Validation with Arroyo Telescope Raytrace + Residual Optical Aberration Spectrum Field Dependent PSFs Synthetic Data Set + Atmosphere Phase Screen Synthetic Sky (Galaxies+Stars) + + = Arroyo Simulation Summary •FOV – 70” •Integration time – 1 sec •Image Size – 4” •Image Pixel Size – 1006x1006 •Image Separation – 10” •Wind speed at 10 km – 30 m/s •Sky model from Ellerbroeck et. al. 2002 JOSA A19 1803 •Phase screen pixelation – 0.02 m, r_0 = 0.25 m The three panel diagram above shows ellipticity vectors from Subaru prime focus images. These data demonstrate that modern technology telescopes meet the demanding LSST PSF shape requirements. Note the high angular correlation over several arcminutes in the center panel after the data have corrected for image trailing. The corresponding 6-Layer phase screens for the 1-sec exposure 4” 10” Altitude (m) T (C) P (mm Hg) H 2 0 (mm Hg) 1000 10 670 8 2000 7 600 8 3000 5 520 8 filter lambda1 lambda2 g 400 559 r 545 703 i 689 862 z 845 946 Y 946 1040 Refraction calculation based on description in Filippenko, 1982, PASP, v94, p715: Filter Passband Definitions Atmosphere Parameters Semi-minor axis: Semi-major axis: ( ) FWHM Seeing ixx 2 1 = ( ) 2 2 2 1 DAR FWHM Seeing iyy + = 0 5000 1 10 4 1.5 10 4 2 10 4 2.5 10 4 3 10 4 3.5 10 4 4 10 4 0 10 20 30 40 50 60 70 80 90 Area of Sky Available (square degrees) Zenith Angle Limit (degrees) Goal Requirement |Lat.| = 20deg 30 40 40 30 20 +/-20deg Galactic plane exclusion 30.9 34.4 41.6 44.7 51.8 0 0.1 0.2 0.3 0.4 0.5 0 20 40 60 80 Ellipticity ZD g r i z Y Zenith seeing = 0.6" Weak Lensing Requirement 3000m Alt.=1000m 2000m 0.0 1.0 2.0 3.0 4.0 5.0 0 10 20 30 40 50 60 70 80 90 Dispersion in FIlter (arcseconds) Zenith Angle g r i z Y Altitude = 2000m Pressure = 600mm Hg Temperature = 7C Water Vapor = 8mm Hg Arroyo: a software package developed for the TMT. It's highly flexible: e.g., atmospheric parameters can be taken from a file of Cerro Tololo observations. These atmospheric parameters then predict well the observed width of the PSF. The present storage requirements of the atmospheric phase screens limit the field-of-view to 10' X 10' (about the size of a single LSST CCD chip) for reasonable atmospheric parameters. A program is underway to parallelize the program operation to allow complete atmospheric simulation of the full 3.5degree X 3.5degree LSST field of view. The LSST requires the raw PSF ellipticity not exceed 0.1. The effects of atmospheric dispersion limits the angle away from zenith where this requirement can be met. The figure at right shows the available sky area for three observatory latitudes with (dotted) and without (solid) exclusion for source crowding in the galactic plane. The vertical drop lines indicates the zenith angle needed to meet the LSST area coverage requirements and goals. In the figure below the PSF ellipticity from atmospheric dispersion is shown for each of the 5 spectral bands the LSST will likely use. For each spectral band three observatory altitudes are plotted. The information combined from this plot and the one above show that with the exception of the g band the LSST ellipticity and sky coverage requirements can be met without any atmospheric dispersion correction. This greatly simplifies the camera design (see poster 108.05)
Transcript of LSST Image Quality and Effects Seen Through the …...Cerro Tololo observations. These atmospheric...
( )( )iyyixx
iyyixxe+−
=1 ( )( )iyyixx
ixye+
=22
22 21 eee +=
Ellipticity definition from2nd intensity moments
ABSTRACTThe 8.4m Large Synoptic Survey Telescope (LSST) is a new 3.5 degree field of view facility for the purpose of studying the nature of dark energy and matter along with the time varying nature of the optical universe. These science missions require precise knowledge and control of both the size and shape of the point spread function (PSF) delivered by the LSST. Here, we present analyses of three areas of image quality that are critical to the LSST: 1) the stability and angular correlation of the stellar PSF second moments as seen through a turbulent atmosphere typical of a high quality observing site and the baseline LSST optical design, 2) the ability to recover a synthetically induced gravitational shear signal on Hubble Deep Field data modified to mimic seeing and telescope aberrations, and 3) the effects of chromatic atmospheric refraction through the LSST filters on image shape and field registration. For the stability, angular correlation and chromatic refraction studies we compare our simulations with data obtained on modern new technology telescopes.
LSST Image Quality and Effects Seen LSST Image Quality and Effects Seen Through the AtmosphereThrough the Atmosphere
C. F. Claver (NOAO), S. Asztalos (LLNL), A. Becker (U. Washington), J. G. Jernigan (LBL),S. M. Kahn, J. R. Peterson (SLAC), L. Rosenberg (LLNL),
V. Margoniner (UC Davis), J. A. Tyson (UC Davis), D. Wittman (UC Davis)
1) PSF Ellipticity Angular Correlation:Turbulent OPD
Point Spread Function
0.000 0.025 0.150… ……
Time (seconds)FourierTransform ∑
=
sec10
0t
On AxisImage
Off AxisImage
DifferenceImage
10" separation
120" separation
3.2 arcsec10 second integration
E E1 E2Ellipticity Residual versus Angular Separation
-0.004
-0.002
0.000
0.002
0.004
0 20 40 60 80 100 120 140
E2 R
esid
ual
Separation(arcseconds)
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0 20 40 60 80 100 120 140
E1 R
esid
ual
Separation(arcseconds)
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0 20 40 60 80 100 120 140
Ellip
ticity
Res
idua
l
Separation(arcseconds)
Subaru 10sec exposures show ellipticity residual amplitudes (colored points) consistent with model results (black points).
Raw de-trailed PSF corrected
13 a
rcm
in
<shear> <shear> = 0.07= 0.07
<shear> <shear> = 0.000013= 0.000013
2) High Fidelity Simulation Development
3) Ellipticity from Atmospheric Refraction
Synthetic Galaxies
Cosmology(108.14, .15, .16, .17, .18, .20, .27)
AtmosphereValidateatmosphere
Camera(poster 108.05)
Controlsystem
OperationsSimulator
(poster 108.09)
Syntheticdata set
Telescope(poster 108.04)
Modeling Process Flow
Atmosphere Model Validation with Arroyo
Telescope Raytrace
+
Residual Optical Aberration Spectrum Field Dependent PSFs Synthetic Data Set
+AtmospherePhase Screen
Synthetic Sky(Galaxies+Stars)
+ + =
Arroyo Simulation Summary•FOV – 70”•Integration time – 1 sec•Image Size – 4”•Image Pixel Size – 1006x1006•Image Separation – 10”•Wind speed at 10 km – 30 m/s•Sky model from Ellerbroeck et. al. 2002 JOSA A19 1803•Phase screen pixelation – 0.02 m, r_0 = 0.25 m
The three panel diagram above shows ellipticity vectors from Subaru prime focus images. These data demonstrate that modern technology telescopes meet the demanding LSST PSF shape requirements. Note the high angular correlation over several arcminutes in the center panel after the data have corrected for image trailing.
The corresponding 6-Layer phase screens for the 1-sec exposure
4”
10”
Altitude (m) T (C) P (mm Hg) H20 (mm Hg) 1000 10 670 8 2000 7 600 8 3000 5 520 8
filter lambda1 lambda2 g 400 559 r 545 703 i 689 862 z 845 946 Y 946 1040
Refraction calculation based on description inFilippenko, 1982, PASP, v94, p715:
Filter Passband DefinitionsAtmosphere Parameters Semi-minor axis:
Semi-major axis:
( )FWHMSeeingixx 21=
( ) 222
1 DARFWHMSeeingiyy +=
0
5000
1 104
1.5 104
2 104
2.5 104
3 104
3.5 104
4 104
0 10 20 30 40 50 60 70 80 90
Area
of S
ky A
vaila
ble
(squ
are
degr
ees)
Zenith Angle Limit (degrees)
Goal
Requirement
|Lat.| = 20deg
30
40
40
30
20
+/-20deg Galactic plane exclusion
30.9
34.4
41.6
44.7
51.8
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60 80
Elli
ptic
ity
ZD
g
r
i
z
Y
Zenith seeing = 0.6"
Weak Lensing Requirement
3000m
Alt.=1000m
2000m
0.0
1.0
2.0
3.0
4.0
5.0
0 10 20 30 40 50 60 70 80 90
Dis
pers
ion
in F
Ilter
(arc
seco
nds)
Zenith Angle
g
r
i
z
Y
Altitude = 2000mPressure = 600mm HgTemperature = 7CWater Vapor = 8mm Hg
Arroyo: a software package developed for the TMT. It's highly flexible: e.g., atmospheric parameters can be taken from a file of Cerro Tololo observations. These atmospheric parameters then predict well the observed width of the PSF. The present storagerequirements of the atmospheric phase screens limit the field-of-view to 10' X 10' (about the size of a single LSST CCD chip) for reasonable atmospheric parameters.
A program is underway to parallelize the program operation to allow complete atmospheric simulation of the full 3.5degree X 3.5degree LSST field of view.
The LSST requires the raw PSF ellipticity not exceed 0.1. The effects of atmospheric dispersion limits the angle away from zenith where this requirement can be met. The figure at right shows the available sky area for three observatory latitudes with (dotted) and without (solid) exclusion for source crowding in the galactic plane. The vertical drop lines indicates the zenith angle needed to meet the LSST area coverage requirements and goals.
In the figure below the PSF ellipticity from atmospheric dispersion is shown for each of the 5 spectral bands the LSST
will likely use. For each spectral band three observatory altitudes are plotted. The information combined from this plot and the one above show that with the exception of the g band the LSST ellipticity and sky coverage requirements can be met without any atmospheric dispersion correction. This greatly simplifies the camera design (see poster 108.05)
