Narrow Atomic Features from Rapidly Spinning Neutron Stars. (arXiv:1209.0768v1 [astro-ph.HE])

Narrow Atomic Features from Rapidly Spinning Neutron Stars. (arXiv:1209.0768v1 [astro-ph.HE]):
Neutron stars spinning at moderate rates (~300-600Hz) become oblate in shape
and acquire a nonzero quadrupole moment. In this paper, we calculate profiles
of atomic features from such neutron stars using a ray-tracing algorithm in the
Hartle-Thorne approximation. We show that line profiles acquire cores that are
much narrower than the widths expected from pure Doppler effects for a large
range of observer inclinations. As a result, the effects of both the oblateness
and the quadrupole moments of neutron stars need to be taken into account when
aiming to measure neutron star radii from rotationally broadened lines.
Moreover, the presence of these narrow cores substantially increases the
likelihood of detecting atomic lines from rapidly spinning neutron stars.