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Dark Energy Camera Observing Strategy James Annis Experimental Astrophysics Group Fermilab

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Footprint Extinction Map Centered SGP Also Alt-Az at midnight, Halloween, CTIO Red circles Gal latitude/ Elevation Offset red circles Equatorial coords SPT visibility region: green Strawman survey area: blue 5000 sq-degrees total 3100 sq-deg South 1600 sq-deg overhead 200 sq-deg SDSS stripe 82

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis DEC and SDSS Footprints

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Visbility RA: 22 hrs to 6 hrs 22 hrs: overhead at midnight Sept 15 6 hrs: overhead at midnight Jan 15 Optimal: October, November, December, January

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Weather October 5.5 hrs/night photometric 1.7 hrs/night cirrus 0.66 fraction time at airmass < 1.5 0.85” median site seeing November 6.0 hrs/night photometric 1.2 hrs/night cirrus 1.00 fraction time at airmass < 1.5 0.65” median site seeing December 6.6 hrs/night photometric 0.7 hrs/night cirrus 1.00 fraction time at airmass < 1.5 0.65” median site seeing January 6.7 hrs/night photometric 1.0 hrs/night cirrus 0.66 fraction time at airmass < 1.5 0.60” median site seeing Totals 630 hours/year of photometric time

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Work in Gray/Bright Time? Doug Tucker SDSS PT z band No effect i band < 0.2 mag for > 60 degree separation

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Size of Camera Field Footprint: 5000 sq-degrees Available time: 3000 hours Exposure time: 1.6 hrs/field 5000 sq-degrees in 3000 hours = 1.67 sq-degree/hour Field of View 1.67 sq-deg * 1.6 hrs/field = 2.6 sq deg/field Exposure time split over ~5 separate images

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Circles Tessellate The geometric meaning of the word tessellate is "to cover the plane with a pattern in such a way as to leave no region uncovered." The overlap doesn’t count towards the five.

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Equilateral Triangle Square Hexagon 3 Regular Polygons Tile To tile is to tessellate is without overlaps Only 3 regular polygons can tile the plane. Others violate the rule that the angles of a vertex must add to 360.

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Hexagons Tile Optimally Theorem (Honeycomb conjecture) Any partition of the plane into regions of equal area has perimeter at least that of the regular hexagonal honeycomb tiling. (Hales 1999) Hexagons maximize the unique area

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis The Relevant Area is the Hexagon E2V devices LBL devices

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Sky Map 2500 hexagons 50x50 Image to the right is 13x13 Use the hexs to count the 5 exposures

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Large Survey Photometry I Unique Properties: Single stable instrument Huge homogeneous photometric data set System defined by 10 8 magnitudes of the survey Survey Systems: System defined by detailed response of survey camera Zeropoints set by observations of standard stars Goals: Change brightness of object and move it 10s of degrees Effect is –only- that of -2.5 log( flux) Given a calibrated spectrum and detailed response curves, one can accurately predict measured magnitudes

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Large Survey Photometry II Equations are of form: i = -2.5 log(Counts) – zp – k i (t) X Where zp is zeropoint X is airmass k i (t) is the extinction coefficent No cross terms Neglect of 2 nd order color/airmass term limits precision to 1% For a given night, 1 filter Maximizes numbers of standards/filter/night Keep airmass the same. k g = 0.15 k r = 0.11 k i = 0.10 k z = 0.05 If airmass changes from 1.2 to 1.4, then change in g is 0.02%

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Large Survey Strategy I 2 hour stripes Roughly same airmass Same filter ~ 40 hexagons Maximizes photometric uniformity of 40 hex stripe Then go observe a standard Tile the plane Then, tile the plane with hex offset half hex over and up This gives 30% overlap with three hexagons Repeat

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Large Survey Strategy II Tie the hex stripes together using these offset tilings. Maximize rigidity by using one hex tiling taking stripes vertical, across all hex stripes. This breaks the constant airmass, but eliminates large scale non- uniformities. Then zeropoint the rigid map. Dither pattern is thus a large scale Y shape ¼ -> ½ hex scale But dither is tied intimately to photometric calibration scheme. Akin to the ground based CMB mapping strategies

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Summary Southern Galactic Cap Use Oct, Nov, Dec, Jan Observe i,z during moony times Hexagons form the best map to count unique observations Need 2.1 o diameter corrector for a 2.6 degree 2 hexagon camera Use 1 filter/night, taking long connected swaths Aim to make photometrically rigid map by maximially interconnecting observations. Then zeropoint the rigid map Footprint Tiling Calibration / Dithering

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis The South Galactic Cap Midnight, Nov 16 SGP

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis Area on Sphere Area (sq-degrees) = (sin dec 1 – sin dec 2 ) * RA * 41,000 ------------------------ 2*360

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis

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Dec 5+6 2003 FermilabDark Energy Camera Workshop Jim Annis

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