Cygnus X-2, super-Eddington mass transfer, and pulsar binaries

Abstract

We consider the unusual evolutionary state of the secondary star in Cygnus X-2. Spectroscopic data give a low mass ($M_2 \simeq 0.5 - 0.7\msun$) and yet a large radius ($R_2 \simeq 7\rsun$) and high luminosity ($L_2 \simeq 150\lsun$). We show that this star closely resembles a remnant of early massive Case B evolution, during which the neutron star ejected most of the $\sim 3\msun$ transferred from the donor (initial mass $M_{\rm 2i}\sim 3.6\msun$) on its thermal time-scale $\sim 10^6$ yr. As the system is far too wide to result from common-envelope evolution, this strongly supports the idea that a neutron star efficiently ejects the excess inflow during super--Eddington mass transfer. Cygnus X-2 is unusual in having had an initial mass ratio $q_{\mathrm{i}}=M_{2i}/M_1$ in a narrow critical range near $q_{\mathrm{i}}\simeq 2.6$. Smaller $q_{\mathrm{i}}$ lead to long-period systems with the former donor near the Hayashi line, and larger $q_{\mathrm{i}}$ to pulsar binaries with shorter periods and relatively massive white dwarf companions. The latter naturally explain the surprisingly large companion masses in several millisecond pulsar binaries. Systems like Cygnus X-2 may thus be an important channel for forming pulsar binaries.

9 pages, 4 encapsulated figures, LaTeX, revised version with a few typos corrected and an appendix added, accepted by MNRAS

References in corpus (3)

• The Optical Light Curves of Cygnus X-2 (V1341 Cyg) and the Mass of its Neutron Star
• The mass of the neutron star in Cyg X-2 (V1341 Cyg)
• Soft X-Ray Transients in the Hertzsprung Gap

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