中子星表面的原子谱线不仅要受到磁场的影响，还会受到因旋转导致的多普勒效应，还有狭义和广义相对论效应。对于弱磁场的种子星，磁场的影响甚至 可以忽略。
The Astrophysical Journal, 644:1085–1089, 2006 June 20
THE SHAPES OF ATOMIC LINES FROM THE SURFACES
OF WEAKLY MAGNETIC ROTATING NEUTRON STARS AND THEIR IMPLICATIONS
Sudip Bhattacharyya,1 M. Coleman Miller,1, 2 and Frederick K. Lamb3, 4
Received 2004 December 6; accepted 2006 March 3
ABSTRACT
Motivated by the report by Cottam et al. of iron resonance scattering lines in the spectra of thermonuclear bursts
from EXO 0748676, we have investigated the information about neutron star structure and the geometry of the
emission region that can be obtained by analyzing the profiles of atomic lines formed at the surface of the star. We
have calculated the detailed profiles of such lines, taking into account the star’s spin and the full effects of special and
general relativity, including light bending and frame dragging. We discuss the line shapes produced by rotational
Doppler broadening and magnetic splitting of atomic lines for the spin rates and magnetic fields expected in neutron
stars in low-mass X-ray binary systems.We show that narrow lines are possible even for rapidly spinning stars if the
emission region or the line of sight are close to the spin axis. For most neutron stars in low-mass systems, magnetic
splitting is too small to obscure the effects of special and general relativity.We show that the ratio of the star’s mass to
its equatorial radius can be determined to within 5% using atomic line profiles, even if the lines are broad and skewed.
This is the precision required to constrain strongly the equation of state of neutron star matter.We show further that if
the radius and latitude of emission are known to 5%–10% accuracy, then frame dragging has a potentially detectable
effect on the profiles of atomic lines formed at the stellar surface.
Subject headinggs: equation of state — line: profiles — relativity — stars: neutron — stars: rotation —
X-rays: stars
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