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Paper: Hydrogen or Helium atmospheres for quiescent accreting neutron stars in globular clusters?
Volume: 470, 370 Years of Astronomy in Utrecht
Page: 181
Authors: Servillat, M.
Abstract: Through the study of the quiescent X-ray emission of neutron stars in low-mass X-ray binaries it is possible to constrain the chemical composition of the neutron star atmosphere and the possible equation of state of dense matter. Using deep Chandra observations, I report the spectral analysis of a neutron star in the globular cluster M28. For the first time for this kind of object, different atmosphere models composed of hydrogen, helium or carbon are used. The carbon model can be ruled out, and the derived mass and radius are clearly distinct depending on the composition of the atmosphere. The hydrogen model gives masses/radii consistent with the canonical values of 1.4 M and 10 km, and would allow for the presence of exotic matter inside neutron stars. On the other hand, the helium model provides solutions with higher masses/radii, consistent with the stiffest equations of state. Measurements of neutron star masses/radii by spectral fitting should consider the possibility of heavier element atmospheres, which produce larger masses/radii for the same data, unless the composition of the accretor is known independently.
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