LSST Filter Development LSST Conceptual Design Review Tucson, AZ Sept 17-20, 2007 Kirk Gilmore SLAC

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ LSST Filter Design Parameters 1. Beam that is incident on the filter has a focal ratio 1. Beam that is incident on the filter has a focal ratio of f/1.25 with a 61.5% obscuration. of f/1.25 with a 61.5% obscuration. 2. The filter is concentric about the chief ray so that all 2. The filter is concentric about the chief ray so that all portions of the filter see the same angle of portions of the filter see the same angle of incidence range, 14.2º to 23.6º incidence range, 14.2º to 23.6º ______________________________________________

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ Optical Design Parameters

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ Optic Tolerences

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ SDSS Band-pass Transition Half Maximum Transmission Wavelength (nm) Half Maximum Transmission Wavelength (nm) g r i z g r i z Blue side Blue side Red side Red side LSST Band-pass Transition Half Maximum Transmission Wavelength (nm) Half Maximum Transmission Wavelength (nm) u g r i z y1 y2 y3 u g r i z y1 y2 y3 Blue side Blue side Red side Red side G-Balmer OI 557 R-matches SDSS I-red side short of sky Z-red side stop before H 2 O bands Y–options detailed

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ Filter y1 and y3: Wider, redder choices The blue side is just long-ward of H 2 O bands.. CCD response steep slope - absorption coefficient of silicon falling rapidly as wavelength increases. The absorption coefficient is strongly affected by temperature. Temperature control and uniformity will be important for photometric accuracy with this filter. Filter y2: This is the narrower choice. Y2 does not extend as far to the red as the y1 filter. The red side excludes nearly all of the 930 to 960 nm H 2 O bands.. The cutoff makes the response less sensitive to temperature of the CCD. Y1 – 960 to 1030 Y2 – 970 to 1020 (orig) Y3 – 970 to 1050 (open)

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ Filter band-pass is based on a combination of scientific considerations Filter Band Pass Transitions Uniform deposition required at 1% level over entire filter 75 cm dia. Curved surface Filter is concentric about the chief ray so that all portions of the filter see the same angle of incidence range, 14.2º to 23.6º Filter is concentric about the chief ray so that all portions of the filter see the same angle of incidence range, 14.2º to 23.6º Specs

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ LSST system throughput parameters

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ LSST system spectral throughput in the six filter bands Wavelength (nm) System throughput (%) Includes sensor QE, atmospheric attenuation, optical transmission functions

G-Band

=((1/R3)+(1/S3)+(1/T3)+(1/U3)+(1/V3)+(1/W3)-5)^-1 Typical pass-band spreadsheet

U filter specification issues: 1) Where is the optimal blue edge of the u filter? How should this blue edge be defined - by filter or by atmosphere? 2) Where is the optimal red edge of the u filter? 3) What is the permissible out-of-band leakage? 4) What is the permissible in-band variability in the filter bandpass? 5) Is this a spatial variation as well as wavelength variation? G band leak vs. reduced throughput: Reduced throughput in g will have huge effect on solar system object detection ➢ Kirk - calculate throughput and limiting magnitude to reduce red leak to SRD limits ➢ Lynne - with reduced limiting mag calc expected number of NEOs / other SS objects. G band leak may affect photos calculations for galaxies ➢ Lynne - ask Andy Connolly, see if additional test to run for this g band leak. ➢ Zeljko - tell Lynne if there are other issues for g band leak. ➢ Kirk - estimate cost to reduce g band leaks to SRD Tasks - Some ongoing-some answered

Y band filter specification issues: 1) What is the optimal red edge for the Y filter? 2) What is the optimal blue edge for the Y filter? Independent vs. non-independent filter tradeoffs: Red and blue edge of Y filter independent. Interactions with atmosphere, detector efficiency. Location of Red edge: Absolute limit at red edge of Y filter is set by silicon at 1.1micron. If push all the way to 1.1 micron, then must control temperature of chip closely to avoid variations in detector efficiency. ACTIONS: ➢ Kirk - specify what kind of detector variations we might expect (X% variation with a Y change in Temperature?) Atmospheric emission in OH lines occurs near the red edge of the Y filter - variation in these lines through the night will change the sky background ➢ Lynne - see if MODTRAN4 predicts these kinds of variations and what level of variations we could expect. (mag variation of sky background with typical variations in sky). This does not affect sources, but will essentially affect limiting magnitude. How will this affect calibration in Y? We would like to go as far to the red as possible, to measure quasars at the highest possible redshifts. ➢ Lynne - calculate Y2 & Y-1&3 magnitude for quasars at increasing redshift. Interactions with atmosphere: We don't actually know how the sky background varies, or even what the sky background really is in Y band. ACTIONS: ﾘ Lynne - check with calibration & opsim teams on progress of Y band measurement. Add their results to the input on Y filter. Check that measurements are consistent with MODTRAN4 predictions used in analysis for Yband edges.

I have put a new copy of the ETC on the LSST website, with the baseline sky magnitudes from the studies I did this Spring. The lunar phase information has also been upgraded based on the CTIO.9m data from Smith and Tucker. This version will now be called ETC This version replaces any beta versions of 4.3 that some of your have been running. I put a warning screen on the sign-on page so that people would realize things have changed.. For a week or so, you will need to click in on the hyperlink "Version 4.3". Here are the adopted solar min, max, and avg values for dark sky, airmass = 1 Values are ugrizy AB magnitudes, at the telescope (not extinction corrected). y = Y2, the y filter. private static double[] solarminMag4_3 = { 22.95, 22.32, 21.43, 20.40,19.22, }; private static double[] solaravgMag4_3 = { 22.80, 22.20, 21.30, 20.30,19.10, }; private static double[] solarmaxMag4_3 = { 22.65, 22.10, 21.13, 20.12,18.92, }; New ETC

Seeing = n source type z Y1 Y2 Y3 400 elliptical-galaxy elliptical-galaxy elliptical-galaxy Seeing = n source type z Y1 Y2 Y3 400 elliptical-galaxy elliptical-galaxy elliptical-galaxy Seeing = n source type z Y1Y2 Y3 400 elliptical-galaxy elliptical-galaxy elliptical-galaxy Seeing = n source type z Y1Y2 Y3 400 elliptical-galaxy elliptical-galaxy elliptical-galaxy S/N Calculations in Y-band By Seeing n source type z Y1Y2 Y3 400 elliptical-galaxy elliptical-galaxy elliptical-galaxy spiral-galaxy spiral-galaxy spiral-galaxy G5V G5V G5V By Source n source type z Y1Y2 Y3 25 elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy elliptical-galaxy By Num of Exposures

From: S.Holland, SPIE 2006 QE for a High-rho vs a thin partially depleted CCD

High-rho study contract device ## (vendor X) measured at BNL LSST requirements: Design Min Measured

LSST Sensor Sensor Thickness Study

OH Emission Source - Bright airglow produced by a chemical reaction of hydrogen and ozone in the Earth’s upper atmosphere Band system is due in part to emission from vibrationally excited OH radicals produced by surface interactions with ground-state oxygen atoms. Emission can vary 10-20% over a 10 minute period Ramsey and Mountain (1992) have reported measurements of the nonthermal emission of the hydroxyl radical and examined the temporal and spatial variability of the emission.

Y Y1 OH Emission at NIR Y2

Wavelength (Å) OH Emission

Comparison of Y1, Y2, and Y3

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ z Y Atmospheric H 2 O Band

Flux Comparison Palomar/Cerro Pachon

G-Band

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ Atmospheric Extinction

LSST Conceptual Design Review September 17-20, 2007 Tucson, AZ M13 in Y-band -no flat -noisy bias/dark -no cosmic ray rejection -no slope-fitting

COATINGS TEST PROGRAM g r i z Y Protected Ag “Aged” bare Al “Fresh” bare Al LLNL Protected Ag

SDSS Primary Mirror Witness Samples

Ghost analysis shows worst case is double-reflection from thinnest spectral filter Relative intensity of ghost image to primary image I = [ S / G] 2 R 1 R 2, S = image diameter = mm G = ghost image diameter = 14 mm R = surface reflectivities = 0.01 I = 2.0 x 10 –10 = ~ 24 visual magnitude difference Ghost halo: 14 mm  Detector plane Double-reflection in filter

________________________________________________ Filter Set Simulations Summary Filter Depth (in 20s) u 22.5 b 24.5 (1/2 g) g 24.3 r 24.2 I 23.4 z 22.4 y 21.5 Input SED’s valid for z<1 photoz relation for I-band: single pass < passes < passes < all S/N=10 Some basic conclusions: 1.u-band reduces the scatter for z < 0.5 sources 2.y-band keeps the scatter tight to z~1.6