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Title: Properties of Ellipticity Correlation with Atmospheric Structure From Gemini South

Abstract

Cosmic shear holds great promise for a precision independent measurement of {Omega}{sub m}, the mass density of the universe relative to the critical density. The signal is expected to be weak, so a thorough understanding of systematic effects is crucial. An important systematic effect is the atmosphere: shear power introduced by the atmosphere is larger than the expected signal. Algorithms exist to extract the cosmic shear from the atmospheric component, though a measure of their success applied to a range of seeing conditions is lacking. To gain insight into atmospheric shear, Gemini South imaging in conjunction with ground condition and satellite wind data were obtained. We find that under good seeing conditions Point-Spread-Function (PSF) correlations persist well beyond the separation typical of high-latitude stars. Under these conditions, ellipticity residuals based on a simple PSF interpolation can be reduced to within a factor of a few of the shot-noise induced ellipticity floor. We also find that the ellipticity residuals are highly correlated with wind direction. Finally, we correct stellar shapes using a more sophisticated procedure and generate shear statistics from stars. Under all seeing conditions in our data set the residual correlations lie everywhere below the target signal level. For goodmore » seeing we find that the systematic error attributable to atmospheric turbulence is comparable in magnitude to the statistical error (shape noise) over angular scales relevant to present lensing surveys.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
897735
Report Number(s):
SLAC-PUB-12297
astro-ph/0701157; TRN: US200705%%314
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Submitted to Astrophys.J.
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ACCURACY; ALGORITHMS; INTERPOLATION; SATELLITES; SHAPE; SHEAR; STARS; STATISTICS; TARGETS; TURBULENCE; UNIVERSE; Astrophysics,ASTRO

Citation Formats

Asztalos, Stephen J., /LLNL, Livermore, de Vries, W.H., /UC, Davis /LLNL, Livermore, Rosenberg, L.J, Treadway, T., /LLNL, Livermore, Burke, D., /SLAC, Claver, C., Saha, A., /NOAO, Tucson, Puxley, P., and /Gemini Observ., La Serena. Properties of Ellipticity Correlation with Atmospheric Structure From Gemini South. United States: N. p., 2007. Web. doi:10.1086/512048.
Asztalos, Stephen J., /LLNL, Livermore, de Vries, W.H., /UC, Davis /LLNL, Livermore, Rosenberg, L.J, Treadway, T., /LLNL, Livermore, Burke, D., /SLAC, Claver, C., Saha, A., /NOAO, Tucson, Puxley, P., & /Gemini Observ., La Serena. Properties of Ellipticity Correlation with Atmospheric Structure From Gemini South. United States. doi:10.1086/512048.
Asztalos, Stephen J., /LLNL, Livermore, de Vries, W.H., /UC, Davis /LLNL, Livermore, Rosenberg, L.J, Treadway, T., /LLNL, Livermore, Burke, D., /SLAC, Claver, C., Saha, A., /NOAO, Tucson, Puxley, P., and /Gemini Observ., La Serena. Wed . "Properties of Ellipticity Correlation with Atmospheric Structure From Gemini South". United States. doi:10.1086/512048. https://www.osti.gov/servlets/purl/897735.
@article{osti_897735,
title = {Properties of Ellipticity Correlation with Atmospheric Structure From Gemini South},
author = {Asztalos, Stephen J. and /LLNL, Livermore and de Vries, W.H. and /UC, Davis /LLNL, Livermore and Rosenberg, L.J and Treadway, T. and /LLNL, Livermore and Burke, D. and /SLAC and Claver, C. and Saha, A. and /NOAO, Tucson and Puxley, P. and /Gemini Observ., La Serena},
abstractNote = {Cosmic shear holds great promise for a precision independent measurement of {Omega}{sub m}, the mass density of the universe relative to the critical density. The signal is expected to be weak, so a thorough understanding of systematic effects is crucial. An important systematic effect is the atmosphere: shear power introduced by the atmosphere is larger than the expected signal. Algorithms exist to extract the cosmic shear from the atmospheric component, though a measure of their success applied to a range of seeing conditions is lacking. To gain insight into atmospheric shear, Gemini South imaging in conjunction with ground condition and satellite wind data were obtained. We find that under good seeing conditions Point-Spread-Function (PSF) correlations persist well beyond the separation typical of high-latitude stars. Under these conditions, ellipticity residuals based on a simple PSF interpolation can be reduced to within a factor of a few of the shot-noise induced ellipticity floor. We also find that the ellipticity residuals are highly correlated with wind direction. Finally, we correct stellar shapes using a more sophisticated procedure and generate shear statistics from stars. Under all seeing conditions in our data set the residual correlations lie everywhere below the target signal level. For good seeing we find that the systematic error attributable to atmospheric turbulence is comparable in magnitude to the statistical error (shape noise) over angular scales relevant to present lensing surveys.},
doi = {10.1086/512048},
journal = {Submitted to Astrophys.J.},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 17 00:00:00 EST 2007},
month = {Wed Jan 17 00:00:00 EST 2007}
}
  • Cosmic shear holds great promise for a precision independent measurement of {Omega}{sub m}, the mass density of the universe relative to the critical density. The signal is expected to be weak, so a thorough understanding of systematic effects is crucial. An important systematic effect is the atmosphere: shear power introduced by the atmosphere is larger than the expected signal. Algorithms exist to extract the cosmic shear from the atmospheric component, though a measure of their success applied to a range of seeing conditions is lacking. To gain insight into atmospheric shear, Gemini South imaging in conjunction with ground condition andmore » satellite wind data were obtained. We find that under good seeing conditions Point-Spread-Function (PSF) correlations persist well beyond the separation typical of high-latitude stars. Under these conditions, ellipticity residuals based on a simple PSF interpolation can be reduced to within a factor of a few of the shot-noise induced ellipticity floor. We also find that the ellipticity residuals are highly correlated with wind direction. Finally, we correct stellar shapes using a more sophisticated procedure and generate shear statistics from stars. Under all seeing conditions in our data set the residual correlations lie everywhere below the target signal level. For good seeing we find that the systematic error attributable to atmospheric turbulence is comparable in magnitude to the statistical error (shape noise) over angular scales relevant to present lensing surveys.« less
  • We investigate the ellipticity of the point-spread function (PSF) produced by imaging an unresolved source with a telescope, subject to the effects of atmospheric turbulence. It is important to quantify these effects in order to understand the errors in shape measurements of astronomical objects, such as those used to study weak gravitational lensing of field galaxies. The PSF modeling involves either a Fourier transform of the phase information in the pupil plane or a ray-tracing approach, which has the advantage of requiring fewer computations than the Fourier transform. Using a standard method, involving the Gaussian weighted second moments of intensity,more » we then calculate the ellipticity of the PSF patterns. We find significant ellipticity for the instantaneous patterns (up to more than 10%). Longer exposures, which we approximate by combining multiple (N) images from uncorrelated atmospheric realizations, yield progressively lower ellipticity (as 1/{radical}N). We also verify that the measured ellipticity does not depend on the sampling interval in the pupil plane using the Fourier method. However, we find that the results using the ray-tracing technique do depend on the pupil sampling interval, representing a gradual breakdown of the geometric approximation at high spatial frequencies. Therefore, ray tracing is generally not an accurate method of modeling PSF ellipticity induced by atmospheric turbulence unless some additional procedure is implemented to correctly account for the effects of high spatial frequency aberrations. The Fourier method, however, can be used directly to accurately model PSF ellipticity, which can give insights into errors in the statistics of field galaxy shapes used in studies of weak gravitational lensing.« less
  • The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose self-calibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexitiesmore » on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique.« less
  • A wide range of recent full-disk spectral observations is used to constrain the atmospheric structure and dynamical properties of Neptune; analytical determinations are made of the abundances of such spectrally active gas species as the deep-atmosphere CH4 molar fraction and the mean ortho/para hydrogen ratio in the visible atmosphere, as well as stratospheric and tropospheric aerosol properties. Compared to Uranus, the greater abundance and shorter lifetimes of Neptunian particulates in the stratospheric region irradiated by the solar UV flux indicate that such radiation is the darkening agent of stratospheric aerosols on both planets. 94 refs.