Day 1019

Tuesday.


1512.01249
Evaluating the effect of stellar multiplicity on the PSF of space-based weak lensing surveys
Kuntzer, Courbin, Meylan

The next generation of space-based telescopes used for WL surveys will require exquisite PSF determination.  Previously negligible effects may become important in the reconstruction of the PSF, in part because of the improved spatial resolution.  In this paper, show that unresolved multiple star systems can affect the ellipticity and size of the PSF an that this effect is not canceled even when using many stars in the reconstruction process.  Estimate the error in the reconstruction of the PSF due to the binaries in the star sample both analytically and with image simulations for different PSFs and stellar populations.  The simulations support the analytical finding that the error on the size of the PSF is a function of the multiple stars distribution and of the intrinsic value of the size of the PSF, i.e. if all stars were single.  Similarly, the modification of each of the complex ellipticity components (e1,e2) depends on the distribution of multiple stars and on the intrinsic complex ellipticity.  Using image simulations, also show that the predicted error in the PSF shape is a theoretical limit that can be reached only if large number of stars (up to thousands) are used together to build the PSF at any desired spatial position.  For a lower number of stars, the PSF reconstruction is worse. Finally, compute the effect of binary for different stellar magnitudes and show that bright stars alter the PSF size and ellipticity more than faint stars.  This may affect the design of PSF calibration strategies and the choice of the related calibration fields.


1512.01570
The impact off nterpixel capacitance on WFIRST PSFs
Kannawadi, Shapiro, Mandelbaum, Hirata, Kruk, Rhodes

Unlike optical CCDs, NIR detectors, which are based on CMOS hybrid readout technology, typically suffer from electrical crosstalk between the pixels.  The inter pixel capacitance (IPC) responsible for the crosstalk affects the PSF of the telescope, increasing the size and modifying the shape of all objects in the images while correlating the poisson noise.  Upcoming WL surveys that use these detectors, such as WFIRST, place stringent requirements on the PSF size and shape (and the level at which these are known), which in turn must be translated into requirements on IPC.  To facilitate this process, present a first study of the effect of IPC on WFIRST PSF sizes and shapes.  Realistic PSFs are forward-simulated from physical principles for each WFIRST band pass.  Explore how the PSF size and shape depends on the range of IPC coupling with pixels that are connected along an edge or corner; for the expected level of IPC in WFIRST, IPC increases the PSF slides by ~5%.  Present a linear fitting formula that describes the uncertainty in the PSF size or shape due to spatial variation of IPC across the detector.  Also study the effect of a small anisotropy in the IPC, which further modifies the PSF shapes.  The results are a first, critical step in determining the hardwired and characterization requirements for the detectors used in the WFIRST survey.