Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the Photometric Consequences of Charge-Transfer Inefficiency in WFPC2   Charge-transfer effects in photometry with Wide Field Planetary Camera 2
aboard the Hubble Space Telescope are investigated by a comparison of WFPC2
observations with groundbased photometry for the Galactic globular clusters
omega Centauri and NGC 2419. Simple numerical formulae describing the fraction
of lost signal as functions of position on the detector, stellar brightness,
and the diffuse sky brightness recorded in an image are presented, and the
resulting corrections are compared to those previously derived by Whitmore &
Heyer (1997, Instrument Science Report WFPC2 97-08). Significant lost-charge
effects are seen that are proportional to both the Y coordinate (i.e., the
number of shifts along the parallel register during readout) and the X
coordinate (number of shifts along the serial register). The percentage of
charge lost decreases as the star brightness or the diffuse sky brightness
increases. Charge losses during the brief period when WFPC2 was operated at a
temperature of -76 degrees C were approximately 85% greater, but apart from
that no significant change in the charge transfer losses with time during the
first 3.5 years of WFPC2's mission is evident, except possibly a weak effect
for the very faintest star images. These results are quite similar to those of
Whitmore & Heyer, which were based on a much smaller data set, but there are
some differences in detail. Even with the present set of corrections,
additional sources of calibration uncertainty which I am unable identify or
characterize with the available data probably limit the external accuracy of
photometry from WFPC2 to of order 1-2%.

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The categories of this paper are: hep-ex
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The categories of this paper are: stat
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The categories of this paper are: solv-int
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The categories of this paper are: cond-mat
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The categories of this paper are: physics
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn