Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The uBVI Photometric System. I. Motivation, Implementation, and
  Calibration   This paper describes the design principles for a CCD-based photometric system
that is highly optimized for ground-based measurement of the size of the Balmer
jump in stellar energy distributions. It is shown that, among ultraviolet
filters in common use, the Thuan-Gunn u filter is the most efficient for this
purpose. This filter is combined with the standard Johnson-Kron-Cousins B, V,
and I bandpasses to constitute the uBVI photometric system.
  Model stellar atmospheres are used to calibrate color-color diagrams for the
uBVI system in terms of the fundamental stellar parameters of effective
temperature, surface gravity, and metallicity. The u-B index is very sensitive
to log g, but also to [Fe/H]. It is shown that an analog of the Str\"omgren c_1
index, defined as (u-B)-(B-V), is much less metallicity dependent, but still
sensitive to log g. The effect of interstellar reddening on u-B is determined
through synthetic photometric calculations, and practical advice is given on
dealing with flat fields, atmospheric extinction, the red leak in the u filter,
and photometric reductions.
  The uBVI system offers a wide range of applicability in detecting stars of
high luminosity in both young (yellow supergiants) and old (post-AGB stars)
populations, using stars of both types as standard candles to measure
extragalactic distances with high efficiency, and in exploring the horizontal
branch in globular clusters. In many stellar applications, it can profitably
replace the classical uBVI system.
  Paper II in this series will present a network of well-calibrated standard
stars for the uBVI system.

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The categories of this paper are: hep-th
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th