Day 1089

Tuesday.

1604.07795
Consequences of CCD imperfections for cosmology determined by weak lensing surveys: from laboratory measurements to cosmological parameter bias
Okra, Petri, May, Plazas, Tamagawa

WL causes subtle changes in the apparent shapes of galaxies dues to the bending of light by the gravity of FG masses.  By measuring the shapes of large numbers of galaxies (millions own recent surveys, up to tens of billions in future surveys), can infer the parameters that determine cosmology.  Imperfections in the detectors used to record images of the sky can introduce changes in the apparent shape of galaxies, which in turn can bias the inferred cosmo parameters.  In this paper, consider the effect of two widely discussed sensor imperfections: tree-rings, due to impurity gradient which cause transverse E fields in the CCD, and pixel-size variation, due to periodic CCD fabrication errors.  These imperfections can be observed when the detectors are subject to uniform illumination (flat field images).  Develop methods to determine the spurious shear and convergence (due to the imperfections) from the flat-field images.  Calculate how the spurious shear when added to the lensing shear will bias the determination of cosmo parameters.  Apply the methods to candidate sensors of the LSST as a timely and important example, analyzing flat field images recorded with LSST prototype CCDs in the lab.  Find that tree rings and periodic pixel-size variation present in the LSST CCDs will introduce negligible bias to cosmological parameters determined from the lensing power spectrum, specifically, w, Omega_m and sigma8.


1604.08360
Constraints on LISA pathfinder's self-gravity: design requirements, estimates and testing procedures
Ferroni

LISA pathfinder satellite has been launched on 3rd December 2015 toward the Sun-Earth L1 point where the LISA Technology Package (LTP), which is the main scene payload, will be tested.  With its cutting-edge technology, the LTP will provide the ability to achieve unprecedented geodesic motion residual acceleration measurements down to the order of 3e-14 m/s^2/Hz^1/2 within the 1-30mHz frequency band.  The presence of the spacecraft itself is responsible of the local gravitational field which will interact with the two proof test-masses.  Potentially, such a force interaction might prevent to achieve the targeted free-fall level originating a significant source of noise.  Balance this gravitational force with sub nm/s^2 accuracy, guided by a protocol based on measurements of the position and the mass of all parts that constitute the satellite, via finite element calculation tool estimates.  In the following, introduce requirements, design and foreseen on-orbit testing procedures.


1605.00555
Testing LSST dither strategies for survey uniformity and large-scale structure systematics
Awan, Gawiser, et al

Analyze LSST survey depth for several geometric patterns of dithers (random, hexagonal lattice, spiral) with amplitude as large as the radius of the LSST field-of-view implemented on different timescales (per season, per night, per visit).  Results illustrate that per night and per visit dither assignments are more effective than per season.  Also find that some dither geometries (e.g. hexagonal lattice) are particularly sensitive to the timescale on which the dieters are implemented, while others like random dithers perform well on all timescales.  Then model the propagation of depth variations to artificial fluctuations in galaxy counts, which are a systematic for large-scale structure studies.  Calculate the bias in galaxy counts induced due to the observing strategy, accounting for photometric calibration uncertainties, dust extinction, and magnitude cuts; uncertainties in this bias limit the ability to account for structure induced by the survey strategy.  Find that after 10 years of the LSST survey, the best observing strategies lead to uncertainties in the bias smaller than the minimum statistical floor for a galaxy catalog as deep as r<27.5; of these, a few bring the uncertainties close to the floor for r<25.7 after only one year of survey.