260 research outputs found
Wavelength Dependent PSFs and their impact on Weak Lensing Measurements
We measure and model the wavelength dependence of the PSF in the Hyper
Suprime-Cam (HSC) Subaru Strategic Program (SSP) survey. We find that PSF
chromaticity is present in that redder stars appear smaller than bluer stars in
the and -bands at the 1-2 per cent level and in the and
-bands at the 0.1-0.2 per cent level. From the color dependence of the PSF,
we fit a model between the monochromatic PSF trace radius, , and wavelength
of the form . We find values of between -0.2
and -0.5, depending on the epoch and filter. This is consistent with the
expectations of a turbulent atmosphere with an outer scale length of m, indicating that the atmosphere is dominating the chromaticity. We
find evidence in the best seeing data that the optical system and detector also
contribute some wavelength dependence. Meyers and Burchat (2015) showed that
must be measured to an accuracy of not to dominate the
systematic error budget of the Large Synoptic Survey Telescope (LSST) weak
lensing (WL) survey. Using simple image simulations, we find that can be
inferred with this accuracy in the and -bands for all positions in the
LSST field of view, assuming a stellar density of 1 star arcmin and that
the optical PSF can be accurately modeled. Therefore, it is possible to correct
for most, if not all, of the bias that the wavelength-dependent PSF will
introduce into an LSST-like WL survey.Comment: 14 pages, 10 figures. Submitted to MNRAS. Comments welcom
Prompt Detection of Fast Optical Bursts with the Vera C. Rubin Observatory
The transient optical sky has remained largely unexplored on very short
timescales. While there have been some experiments searching for optical
transients from minutes to years, none have had the capability to distinguish
millisecond Fast Optical Bursts (FOB). Such very fast transients could be the
optical counterparts of Fast Radio Bursts (FRB), the prompt emission from
-Ray Bursts (GRB), or other previously unknown phenomena. Here, we
investigate a novel approach to the serendipitous detection of FOBs, which
relies on searching for anomalous spatial images. In particular, due to their
short duration, the seeing distorted images of FOBs should look
characteristically different than those of steady sources in a standard optical
exposure of finite duration. We apply this idea to simulated observations with
the Vera C. Rubin Observatory, produced by tracing individual photons through a
turbulent atmosphere, and down through the optics and camera of the Rubin
telescope. We compare these simulated images to steady-source star simulations
in 15 s integrations, the nominal Rubin exposure time. We report the
classification accuracy results of a Neural Network classifier for
distinguishing FOBs from steady sources. From this classifier, we derive
constraints in duration-intensity parameter space for unambiguously identifying
FOBs in Rubin observations. We conclude with estimates of the total number of
detections of FOB counterparts to FRBs expected during the 10-year Rubin Legacy
Survey of Space and Time (LSST).Comment: 7 pages, 4 figures, submitted to the Astrophysical Journa
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