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arXiv 2310.03397astro-ph.HEastro-ph.SR
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利用远紫外光研究中子星低质量X射线双星Swift J1858.6-0814的供体星与演化状态

Shedding far-ultraviolet light on the donor star and evolutionary state of the neutron-star LMXB Swift J1858.6-0814

N. Castro Segura, C. Knigge, J. H. Matthews, F. M. Vincentelli, P. Charles, K. S. Long, D. Altamirano, D. A. H. Buckley, D. Modiano, M. A. P. Torres, D. J. K. B… 展开作者

N. Castro Segura, C. Knigge, J. H. Matthews, F. M. Vincentelli, P. Charles, K. S. Long, D. Altamirano, D. A. H. Buckley, D. Modiano, M. A. P. Torres, D. J. K. Buisson, S. Fijma, K. Alabarta, N. Degenaar, M. Georganti, M. C. Baglio

AI总结:

本研究通过远紫外光谱等观测,分析了暂现中子星低质量X射线双星Swift J1858的供体星性质,约束了其演化路径与质量参数,明确了其可能的演化结局。

摘要:

吸积X射线双星系统的演化与其供体星的性质紧密相关。因此,我们可以通过确定供体星的本质来约束系统所处的演化轨迹。本文中,我们呈现了暂现中子星低质量X射线双星Swift J1858在三种不同吸积状态(低硬态、高硬态和软态)下的远紫外光谱。所有这些光谱均显示出反常的N V、C IV、Si IV和He II谱线,表明其供体星经历了CNO循环过程。我们还基于宁静期获得的测光观测结果,测定了供体星的有效温度$T_{d} \backsimeq 5700$ K,以及半径$R_d \backsimeq 1.7~R_{\bigodot}$。最后,我们利用该系统的暂现特性,给出了当前质量转移率的上限$\rm \dot{M}_{acc} \lesssim 10^{-8.5}~M_{\bigodot}~yr^{-1}$。将所有这些结果与系统的轨道周期$P_{\rm orb}=21.3$小时相结合,我们搜寻了可行的演化路径。允许解中的初始供体质量范围为$1~M_{\bigodot} \lesssim M_{d,i} \lesssim 3.5~M_{\bigodot}$。该范围内除最低质量外的所有解,都与紫外谱线比中强烈的CNO循环特征一致。允许轨迹中的当前供体质量为$0.5~M_{\bigodot}\lesssim M_{d,obs} \lesssim 1.3~M_{\bigodot}$,高于近期食模型给出的结果。由于$P_{\rm orb}$接近所谓的分岔周期,收敛和发散的双星轨迹均是允许的。如果Swift J1858处于收敛轨迹上,它最终将形成带有亚恒星供体星的超致密系统。

英文摘要:

The evolution of accreting X-ray binary systems is closely coupled to the properties of their donor stars. As a result, we can constrain the evolutionary track a system is by establishing the nature of its donor. Here, we present far-UV spectroscopy of the transient neutron-star low-mass X-ray binary Swift J1858 in three different accretion states (low-hard, high-hard and soft). All of these spectra exhibit anomalous N\,{\sc v}, C\,{\sc iv}, Si\,{\sc iv} and He\,{\sc ii} lines, suggesting that its donor star has undergone CNO processing. We also determine the donor's effective temperature, $T_{d} \simeq 5700$~K, and radius, $R_d \simeq 1.7~R_{\odot}$, based on photometric observations obtained during quiescence. Lastly, we leverage the transient nature of the system to set an upper limit of $\dot{M}_{\rm acc} \lesssim 10^{-8.5}~M_{\odot}~yr^{-1}$ on the present-day mass-transfer rate. Combining all these with the orbital period of the system, $P_{\rm orb} = 21.3$~hrs, we search for viable evolution paths. The initial donor masses in the allowed solutions span the range $1~M_{\odot} \lesssim M_{d,i} \lesssim 3.5~M_{\odot}$. All but the lowest masses in this range are consistent with the strong CNO-processing signature in the UV line ratios. The present-day donor mass in the permitted tracks are $0.5~M_{\odot}\lesssim M_{d,obs} \lesssim 1.3~M_{\odot}$, higher than suggested by recent eclipse modelling. Since $P_{\rm orb}$ is close to the so-called bifurcation period, both converging and diverging binary tracks are permitted. If Swift J1858 is on a converging track, it will end its life as an ultra-compact system with a sub-stellar donor star.

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