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We have discovered with XMM-Newton an X-ray source in the core of the globular cluster M13, whose X-ray spectral properties suggest that it is a quiescent neutron star X-ray binary. The spectrum can be well fitted with a pure hydrogen atmosphere model, with T=76 +/- 3 eV, R=12.8 +/- 0.4 km and an X-ray luminosity of 7.3 +/- 0.6 x 10^{32} erg/s. In the light of this result, we have discovered a strong correlation between the stellar encounter rate and the number of quiescent neutron stars found in the ten globular clusters observed so far by either XMM-Newton or Chandra. This result lends strong support to the idea that these systems are primarily produced by stellar encounters in the core of globular clusters.
X-ray spectra of quiescent low-mass X-ray binaries containing neutron stars can be fit with atmosphere models to constrain the mass and the radius. Mass-radius constraints can be used to place limits on the equation of state of dense matter. We perfo
Using deep Chandra observations of the globular cluster M28, we study the quiescent X-ray emission of a neutron star in a low-mass X-ray binary in order to constrain the chemical composition of the neutron star atmosphere and the equation of state of
This paper reports the search for quiescent low-mass X-ray binaries (qLMXBs) in the globular cluster (GC) NGC 6553 using an XMM-Newton observation designed specifically for that purpose. We spectrally identify one candidate qLMXB in the core of the c
We report on the discovery of the companion star to the millisecond pulsar J1631+3627F in the globular cluster M13. By means of a combination of optical and near-UV high-resolution observations obtained with the Hubble Space Telescope, we identified
We have analyzed FUSE, COS, GHRS, and Keck HIRES spectra of the UV-bright star Barnard 29 in M13 (NGC 6205). By comparing the photospheric abundances derived from multiple ionization states of C, N, O, Si, and S, we infer an effective temperature T_e