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Can Neutron Star Masses and Radii be Determined using Spectroscopy?

Presentation #502.05 in the session Stellar/Compact IV.

Published onMay 03, 2024
Can Neutron Star Masses and Radii be Determined using Spectroscopy?

One of the outstanding challenges in neutron star astrophysics is accurate determination of masses and radii. Improved values of mass and radius would not only allow us to learn about fundamental neutron star parameters, but also constrain the equation of state of the interior. We propose a novel method of accomplishing this feat: fitting measured spectral lines with model spectra that include accurate pressure broadening. A 400-ksec exposure of the compact object in Puppis A with Chandra showed evidence of atomic spectral lines and the viability of this method. With the recent launch of XRISM and the proposed telescope ARCUS, more high-resolution spectra are on the horizon. There are various line broadening mechanisms in neutron star atmospheres. Some of these are competing effects. First, there is the effect of the magnetic field, which can broaden the spectral lines through the Zeeman effect and the motional Stark effect. Second, density-dependent plasma perturbations will further broaden the lines. The motional Stark effect will make the spectral line widths insensitive to density. Spectral lines will be sensitive to gravity if the density effects exceed the magnetic field effects. The sensitivity of the spectral lines to these different mechanisms will be examined to evaluate whether a gravity determination is possible.

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