Keplerian frequency of uniformly rotating neutron stars and strange stars
Keplerian frequency of uniformly rotating neutron stars and strange stars
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DOI：
10.1051/0004-6361/200811605
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发表时间：
2009-01
影响因子：
6.5
通讯作者：
P. Haensel;J. Zdunik;M. Bejger;J. Lattimer
中科院分区：
文献类型：
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作者：
P. Haensel;J. Zdunik;M. Bejger;J. Lattimer
目标。我们计算开普勒（质量脱落）配置的刚性旋转中子星和奇怪的星壳。我们检验了由Lattimer和Prakash提出的开普勒频率的经验公式fK的有效性，fK（M）= C（M/M）1/2（R/10 km）-3/2，其中M是开普勒位形的（引力）质量，R是相同引力质量的非旋转位形的（圆周）半径，C = 1.04 kHz。方法.数值计算使用精确的二维代码的基础上的多域谱方法。我们使用一组有代表性的状态方程（EOSs）的中子星和夸克星。结果我们表明，对于具有真实EOS的中子星，f K（M）的经验公式在百分之几以内成立，假设0.5 M φ < M < 0.9 M stat max，其中M stat max）是EOS非旋转中子星的最大允许质量，C = C NS = 1.08 kHz。对于0.5 M x < M < 0.9 M的奇异星，也可以获得类似的精度。对于最大地壳质量，我们得到C ss = 1.15 kHz，并且C ss的值对地壳质量不是很敏感。我们所有的Cs都明显大于相对论Roche模型的分析值，C Roche = 1.00 kHz。对于0.5 M φ < M < 0.9 M stat max，质量为M的开普勒组态的赤道半径R K（M），在一个非常好的近似下，与相同质量的非旋转星星的半径R K（M）= a R（M）成正比，α NS 1.44。α ss的值与奇异星星的地壳质量的依赖性很弱。这两个α值都小于相对论Roche模型的解析值α Roche = 1.5。
Aims. We calculate Keplerian (mass shedding) configurations of rigidly rotating neutron stars and strange stars with crusts. We check the validity of the empirical formula for Keplerian frequency, f K , proposed by Lattimer & Prakash, f K (M) = C (M/M ⊙ ) 1/2 (R/10 km) -3/2 , where M is the (gravitational) mass of the Keplerian configuration, R is the (circumferential) radius of the non-rotating configuration of the same gravitational mass, and C = 1.04 kHz. Methods. Numerical calculations are performed using precise 2D codes based on the multi-domain spectral methods. We use a representative set of equations of state (EOSs) of neutron stars and quark stars. Results. We show that the empirical formula for f K (M) holds within a few percent for neutron stars with realistic EOSs, provided 0.5 M ⊙ < M < 0.9 M stat max , where M stat max ) is the maximum allowable mass of non-rotating neutron stars for an EOS, and C = C NS = 1.08 kHz. Similar precision is obtained for strange stars with 0.5 M ⊙ < M < 0.9 M stat max . For maximal crust masses we obtain C ss = 1.15 kHz, and the value of C ss is not very sensitive to the crust mass. All our Cs are significantly larger than the analytic value from the relativistic Roche model, C Roche = 1.00 kHz. For 0.5 M ⊙ < M < 0.9 M stat max , the equatorial radius of the Keplerian configuration of mass M, R K (M), is, to a very good approximation, proportional to the radius of the non-rotating star of the same mass, R K (M) = a R(M), with α NS ≈ α ss ≈ 1.44. The value of α ss is very weakly dependent on the mass of the crust of the strange star. Both a values are smaller than the analytic value α Roche = 1.5 from the relativistic Roche model.