| Autor: |
Castro Segura, N, Knigge, C, Matthews, J H, Vincentelli, F M, Charles, P, Long, K S, Altamirano, D, Buckley, D A H, Modiano, D, Torres, M A P, Buisson, D J K, Fijma, S, Alabarta, K, Degenaar, N, Georganti, M, Baglio, M C |
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| Zdroj: |
Monthly Notices of the Royal Astronomical Society; 1/15/2024, Vol. 527 Issue 2, p2508-2522, 15p |
| Abstrakt: |
The evolution of accreting X-ray binary systems is closely coupled to the properties of their donor stars. Consequently, we can constrain the evolutionary track a system is by establishing the nature of its donor. Here, we present far-ultraviolet (far-UV) spectroscopy of the transient neutron-star low-mass X-ray binary J1858 in different accretion states (low-hard, high-hard, and soft). All of these spectra exhibit anomalous N v , C iv , Si iv , and He ii lines, suggesting that its donor star has undergone CNO processing. We also determine the donor's effective temperature, Td ≃ 5700 K, and radius, Rd ≃ 1.7 R⊙, based on photometric observations obtained during quiescence. Lastly, we leverage the transient nature of the system to set an upper limit of |$\dot{M}_{\rm acc} \lesssim 10^{-8.5}~{\rm M}_{\odot }~\mathrm{ yr}^{-1}$| on the present-day mass-transfer rate. Combining these with the orbital period of the system, P orb = 21.3 h, we search for viable evolution paths. The initial donor masses in the allowed solutions span the range 1 M⊙ ≲ Md,i ≲ 3.5 M⊙. 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⊙ ≲ M d ,obs ≲ 1.3 M⊙, higher than suggested by eclipse modelling. Since P orb is close to the so-called bifurcation period, both converging and diverging binary tracks are permitted. If the former is confirmed, J1858 will end its life as an ultracompact system with a substellar donor. [ABSTRACT FROM AUTHOR] |
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