标题： 快速恒星自转对从准周期性亮度振荡中得出的状态方程约束的影响 显示英文标题

标题： Effects of Rapid Stellar Rotation on Equation of State Constraints Derived from Quasi-Periodic Brightness Oscillations

摘要： 在低质量X射线双星系统中的十几颗中子星中，已经使用Rossi X射线时变探测器发现了频率约为千赫兹的准周期X射线亮度振荡（QPOs）。有强有力的证据表明，千赫兹振荡的频率是这些恒星周围吸积气体的轨道频率。一些产生千赫兹QPO的恒星可能具有超过400赫兹的自转频率。对于如此高的自转速率，对恒星自转对其结构和时空影响的一阶解析处理是不准确的。在这里，我们利用大量完全相对论的、自洽的数值计算结果，研究了如果观察到不同频率的稳定圆形轨道，可以推导出的这类恒星的性质约束。我们计算了恒星的赤道半径、最内稳定圆形轨道的半径以及最高频率稳定圆形轨道的频率，作为恒星自转速率的函数，对于自转速率达到最大可能值以及几种示例状态方程的情况。我们的计算表明，对于自转频率超过400赫兹的恒星，由给定轨道频率所暗示的中子星物质刚度的上限通常比对于缓慢旋转的恒星要严格得多。 显示英文摘要

摘要： Quasi-periodic X-ray brightness oscillations (QPOs) with frequencies around a kilohertz have now been discovered in more than a dozen neutron stars in low-mass X-ray binary systems using the Rossi X-ray Timing Explorer. There is strong evidence that the frequencies of the kilohertz oscillations are the orbital frequencies of accreting gas in nearly circular orbits around these stars. Some stars that produce kilohertz QPOs may have spin frequencies greater than 400 Hertz. For spin rates this high, first-order analytic treatments of the effects of the star's rotation on its structure and the spacetime are inaccurate. Here we use the results of a large number of fully relativistic, self-consistent numerical calculations of the stellar structure of rapidly rotating neutron stars and the interior and exterior spacetime to investigate the constraints on the properties of such stars that can be derived if stable circular orbits of various frequencies are observed. We have computed the equatorial radius of the star, the radius of the innermost stable circular orbit, and the frequency of the highest-frequency stable circular orbit as functions of the stellar spin rate, for spin rates up to the maximum possible and for several illustrative equations of state. Our calculations show that the upper bounds on the stiffness of neutron star matter implied by a given orbital frequency are typically significantly stricter for stars with spin frequencies more than 400 Hertz than for slowly rotating stars.