@article{21997,
  abstract     = {The massive binary common envelope (CE) phase plays a pivotal role in the formation of close black hole (BH)/neutron star binaries, yet significant uncertainties remain in our understanding of this process. In this study, we aim to constrain the massive binary CE phase by systematically reconstructing three observed BH X-ray binaries (BHXBs): GRO J1655-40, SAX J1819.3-2525, and 4U 1543-47. Through comprehensive binary evolution simulations and parametric supernova modeling, we establish lower limits for the CE efficiency parameters under different energy considerations within the standard energy formalism. Specifically, we derive minimum values for three cases: α0.5U and αU, representing CE efficiencies with half and all of the internal energy contributing to the envelope ejection, respectively, and αH, accounting for the envelope’s enthalpy. Our analysis reveals that the self-consistent formation of these three BHXBs requires CE efficiency parameters satisfying α0.5U ≳ 6.7, αU ≳ 4.2, and αH ≳ 1.7. Notably, we find no viable solutions with CE efficiency values below unity, even when considering the most extreme scenarios, in which the envelope binding energy is significantly reduced through enthalpy inclusion. Our results strongly imply that either additional energy sources are required or the formalism itself must be revised. Furthermore, we quantitatively assess the impact of BH natal kicks on our results. A key finding is that 4U 1543-47’s formation requires substantial natal kicks (≳50 km s−1), as lower kick velocities are incompatible with isolated binary evolution.},
  author       = {Li, Zhenwei and Wei, Dandan and Jia, Shi and Chen, Hailiang and Ge, Hongwei and Chen, Zhuo and Zhang, Yangyang and Chen, Xuefei and Han, Zhanwen},
  issn         = {1538-4357},
  journal      = {The Astrophysical Journal},
  number       = {1},
  publisher    = {IOP Publishing},
  title        = {{A path to constraints on common envelope ejection in massive binaries: Full evolutionary reconstruction of three Black Hole X-ray binaries}},
  doi          = {10.3847/1538-4357/ae66fd},
  volume       = {1004},
  year         = {2026},
}

@article{21714,
  abstract     = {Be stars are rapidly rotating main-sequence stars that play a crucial role in understanding stellar evolution and binary interactions. In this Letter, we propose a new formation scenario for black hole (BH) + Be star binaries (hereafter BHBe binaries), where the Be star is produced through the wind Roche lobe overflow (WRLOF) mechanism. Our analysis is based on numerical simulations of the WRLOF process in massive binaries, building on recent theoretical work. We demonstrate that the WRLOF model can efficiently form BHBe binaries under reasonable assumptions on stellar wind velocities. Using rapid binary population synthesis, we estimate the population of such systems in the Milky Way, predicting ∼1800−3200 currently existing BHBe binaries originating from the WRLOF channel. These systems are characterized by high eccentricities and exceptionally wide orbits, with typical orbital periods exceeding 1000 days and a peak distribution around ∼10,000 days. Due to their long orbital separations, these BHBe binaries are promising targets for future detection via astrometric and interferometric observations.},
  author       = {Li, Zhenwei and Jia, Shi and Wei, Dandan and Ge, Hongwei and Chen, Hailiang and Zhang, Yangyang and Chen, Xuefei and Han, Zhanwen},
  issn         = {2041-8213},
  journal      = {The Astrophysical Journal Letters},
  number       = {2},
  publisher    = {IOP Publishing},
  title        = {{Formation of Be stars via wind accretion: Case study on Black Hole + Be star binaries}},
  doi          = {10.3847/2041-8213/ae3008},
  volume       = {996},
  year         = {2026},
}