Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The M4 Core Project with HST -- V. Characterizing the PSFs of WFC3/UVIS
  by Focus   As part of the astrometric Hubble Space Telescope (HST) large program
GO-12911, we conduct an in-depth study to characterize the point spread
function (PSF) of the Uv-VISual channel (UVIS) of the Wide Field Camera 3
(WFC3), as a necessary step to achieve the astrometric goals of the program. We
extracted a PSF from each of the 589 deep exposures taken through the F467M
filter over the course of a year and find that the vast majority of the PSFs
lie along a one-dimensional locus that stretches continuously from one side of
focus, through optimal focus, to the other side of focus. We constructed a
focus-diverse set of PSFs and find that with only five medium-bright stars in
an exposure it is possible to pin down the focus level of that exposure. We
show that the focus-optimized PSF does a considerably better job fitting stars
than the average "library" PSF, especially when the PSF is out of focus. The
fluxes and positions are significantly improved over the "library" PSF
treatment. These results are beneficial for a much broader range of scientific
applications than simply the program at hand, but the immediate use of these
PSFs will enable us to search for astrometric wobble in the bright stars in the
core of the globular cluster M4, which would indicate a dark, high-mass
companion, such as a white dwarf, neutron star, or black hole.

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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
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The categories of this paper are: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: nlin
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The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an