Pan-STARRS Seminar: IPPEugene Magnier Pan-STARRS Image Processing Pipeline Astrometry and Photometry IFA Pan-STARRS Seminar 735 October 14, 2004

Pan-STARRS Seminar: IPPEugene Magnier ● Astrometry and Photometry Precision Requirements ● Summary of the AP Survey ● Achieving the Photometry Goals ● Achieving the Astrometry Goals Summary of Topics

Pan-STARRS Seminar: IPPEugene Magnier Precision Requirements for Pan-STARRS (PS-4): ● 30 milliarcsec relative astrometry ● 100 milliarcsec absolute astrometry ● 5 millimag relative photometry ● 10 millimag absolute photometry (internal system) These goals can only be efficiently met after we have produced a Pan-STARRS Astrometric and Photometric reference catalog

Pan-STARRS Seminar: IPPEugene Magnier PS-1 AP Survey Parameters: ● gizy : bright sweep, 1 x 5 seconds, 2 x 30 seconds ● r : bright sweep, 1 x 5 seconds, 6 x 30 seconds (over 6 months) ● 1 % photometry ~ 19.5 magnitudes (~ 1 x 10 9 stars) ● saturation: 14 magnitude (5 seconds), 8 magnitude (sweep) ● 50% overlap dither pattern ● 2% of survey time to calibrations: ● 12 standards observations per night per filter (40 min)

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Science Motivations ● galactic stellar populations ● galaxy cluster evolution ● rare object searches ● high-z QSOs ● extremely red galaxies ● low-mass objects (L & T dwarfs) ● YSOs

Pan-STARRS Seminar: IPPEugene Magnier

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Analysis Overview ● linearize detector flux ● apply shutter correction ● flatten images ● photometer objects ● apply image zero point, color correction, airmass correction

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Detector Linearization ● stable light source + variable exposure time? ● calibrated light source?

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Shutter Correction ● measure shutter fly-over times: dt(x,y) ● apply to flat-field or science images ● probably small for 30 second exposures (0.1% = 30 ms jitter ● may be significant for 5 second exposures...

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Flat-Fielding Issues : Illumination Source Options ● twilight-flat ● pros: continuum source, spatially uniform (usually), bright ● cons: very blue, limited availability, cirrus issues ● dome-flat ● pros: continuum source, available anytime, repeatable (?) ● cons: spatial structures, low count rates, emission line dangers ● night-sky flat ● pros: obtained 'automatically' ● cons: low count rates, stellar contaminations, spatial structures unknown, emission line source

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Flat-Fielding Issues : Flat-field Corrections ● correct for geometrical distortion & scattered light ● stability time scale?

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Color Corrections ● chip-to-chip color terms (possibly linear, small) ● internal system vs external system ● external transformations are often ambiguous M g inst = -2.5 log (counts / sec) M g sys = M g inst + C g + K g (1-z) + F g (color) M g cal = M g sys + Q g (color)

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Absolute Photometry ● use relative photometry with reference overlaps ● measure zero points & atmospheric corrections, apply ● combination method (relphot + uniphot) ref 1 ref 2 ref 1 ref 2

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Zero-point Stability (long-term trends) ● system zero-points vary ~0.1 mag on timescales ~ 100 days

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Atmospheric Stability (short-term trends) ● variations in time : C f (t) ● variations in space : C f (ra,dec) ● these variations are NOT strongly correlated

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Atmospheric Stability (short-term trends)

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Atmospheric Stability conclusions: ● photometric conditions exist at <1% level ● sometimes there is haze : C f (t) ● sometimes there is thin cirrus : C f (x,y) ● haze is apparently more common... ● make use of external indicators of transparency conditions: ● SkyProbe ● NIR Camera

Pan-STARRS Seminar: IPPEugene Magnier Photometry: Bright Stars & Flux Calibrations ● OTA guide stars tie 30 sec exposures to 10 msec exposures ● OTA 'sweep' can yield survey of stars mag ● Bright stars provide flux calibration (spectrophotometric standards) ● SkyProbe A will provide atm transmission function

Pan-STARRS Seminar: IPPEugene Magnier Astrometry: Science Motivations ● proper motions / baseline ● high-quality grid for weak-lensing (starting point) ● stellar matching in crowded fields

Pan-STARRS Seminar: IPPEugene Magnier Astrometry: Basic Concepts ● RA,DEC X,Y ● linear fit ● RA = RA o + X*dRdX + Y*dRdY, etc ● arcsec FOV ● projection + fit ● RA,DEC -> P,Q ● P,Q = f(X,Y) P,Q R,D

Pan-STARRS Seminar: IPPEugene Magnier P,Q R,D L,M projection optical distortion L,M X,Y chip locations Astrometry: Mosaic Astrometry ● boresite + projection (RA o, DEC o, ) ● distortion: N th order polynomial L,M = f(P,Q) ● chip coordinates: X o, Y o, ● watch for stability issues

Pan-STARRS Seminar: IPPEugene Magnier Astrometry: Mosaic Astrometry Stability ● chip coordinates & distortion are fairly degenerate ● direct fitting is a large, multiparameter, non-linear problem ● use local gradients instead: ● fit L,M assuming no distortion ● fit chip parameters from L,M ● measure L,M residuals (L, M) ● measure local gradients (dL/dP, dL/dQ, dM/dP, dM/dQ) ● fit local gradients to N th order polynomial ● resulting terms are coefficients of L,M vs P,Q (N+1) th order fit ● fit is insensitive to chip positions, boresite center

Pan-STARRS Seminar: IPPEugene Magnier Astrometry: Example from MegaPrime ● chips are probably NOT flat!

Pan-STARRS Seminar: IPPEugene Magnier Astrometry: Example from MegaPrime ● chips are probably NOT flat!

Pan-STARRS Seminar: IPPEugene Magnier Astrometry: Calibrating the AP Survey ● what is stability of model components? ● boresite: changes with every exposure ● optical distortion: long-term stability expected ● chip warps: short-term stability? temperature dependence? ● chip positions: gravity vector dependence? ● regularly measure model components & track changes ● tie to ICRS with Guide Stars (Tycho) ● atmosphere may introduce 50 mas scatter: model in overlaps USNO-B: deep, dense (~20 mag), mas scatter, large-scale errors UCAC: modest (16 mag), 20 mas scatter + proper motion Tycho: shallow (11.5 mag), 10 mas scatter + proper motion Hipparchos: very shallow (7.3 mag), 1 mas scatter + proper motion