Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Massive White Dwarfs in the Galactic Center: A Chandra X-ray
  Spectroscopy of Cataclysmic Variables   Previous X-ray observations toward the Nuclear Star Cluster (NSC) at the
Galactic center have discovered thousands of point sources, most of which were
believed to be cataclysmic variables (CVs), i.e., a white dwarf (WD) accreting
from a low-mass companion. However, the population properties of these CVs
remain unclear, which otherwise contain important information about the
evolutionary history of the NSC. In this work we utilize ultradeep archival
\textit{Chandra} observations to study the spectral properties of the NSC CVs,
in close comparison with those in the Solar vicinity. We find that the NSC CVs
have strong Fe XXV and Fe XXVI lines (both of which show equivalent widths
$\sim200-300$ eV), indicating metal-rich companions. Moreover, their Fe XXVI to
Fe XXV line flux ratio is used to diagnose the characteristic white dwarf mass
($M_{\rm WD}$) of NSC CVs. The results show that the CVs with $L_{\rm 2-10
keV}>6\times10^{31}$ erg s$^{-1}$ have a mean $M_{\rm WD}$ of
$\sim0.6/1.0\,M_{\odot}$ if they are magnetic/non-magnetic CVs; while those
with $L_{\rm 2-10 keV}$ between $1-6\times10^{31}$ erg s$^{-1}$ have a mean
$M_{\rm WD}$ of $\sim0.8/1.2\,M_{\odot}$ if they are magnetic/non-magnetic CVs.
All these \textit{Chandra}-detected CVs collectively contribute $\sim$30-50\%
of the unresolved 20-40 keV X-ray emission from the NSC. The CV population with
massive (i.e., $M_{\rm WD}\sim1.2M_{\odot}$) WDs have not been observed in the
Solar vicinity or the Galactic bulge, and they might have been formed via
dynamical encounters in the NSC.

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The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
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: chem-ph
3
The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc