Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: HZ Her: Stellar Radius from X-ray Eclipse Observations, Evolutionary
  State and a New Distance   Observations of HZ Her/Her X-1 by the Rossi X-ray Timing Explorer (RXTE)
covering high state eclipses of the neutron star are analyzed here. Models of
the eclipse are used to measure the radius and atmospheric scale height of HZ
Her, the stellar companion to the neutron star. The radius is 2.58 to 3.01
$\times10^{11}$ cm, depending on system inclination and mass ratio(q), with
accuracy of $\sim$1 part in 1000 for given inclination and $q$. We fit Kurucz
model stellar atmosphere models to archival optical observations. The resulting
effective temperature ($T_{eff}$) of the unheated face of HZ Her is determined
to be in the 2$\sigma$ range 7720K to 7865K, and metallicity
($log(Z/Z_{\odot})$) in the range -0.27 to +.03. The model atmosphere surface
flux and new radius yield a new distance to HZ Her/ Her X-1, depending on
system inclination and $q$: a best-fit value of 6.1 kpc with upper and lower
limits of 5.7 kpc and 7.0 kpc. We calculate stellar evolution models for the
range of allowed masses (from orbital parameters), and allowed metallicities
(from optical spectrum fits). The stellar models agree with $T_{eff}$ and
radius of HZ Her for two narrow ranges of mass: 2.15 to 2.20 $M_{\odot}$ and
2.35 to 2.45 $M_{\odot}$ This lower mass range implies a low neutron star mass
(1.3 $M_{\odot}$), whereas the higher mass range implies a high neutron star
mass (1.5-1.7 $M_{\odot}$).

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The categories of this paper are: mtrl-th
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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: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio
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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: funct-an
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The categories of this paper are: cs
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The categories of this paper are: q-alg
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The categories of this paper are: dg-ga
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The categories of this paper are: math
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The categories of this paper are: adap-org
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ph