The formation and evolution of massive binaries may share the same mechanism in the Milky Way and the Andromeda galaxy
A research team led by Professor QIAN Shengbang and PhD student LI Fuxing from the Yunnan Observatories of the Chinese Academy of Sciences has found that the formation and evolution of massive binaries in the Milky Way and Andromeda Galaxy ( M31) could share the same mechanism. .
Their findings have been published in Monthly Notices of the Royal Astronomical Society and The Astrophysical Journal.
The massive binary contains at least one early-type star whose spectral type is O,B type. These binaries have high-energy radiation like X-rays, and they possibly create neutron stars or black holes. The ancestors of these semi-detached binaries are the detached binaries where the more massive original components evolve faster and first fill their critical Roche lobes and then transfer mass to their companions with the evolution of case A.
During this process, the orbital period of the system will be reduced and the mass ratio will be increased. When the system evolves to the critical state where the mass ratio is one (twin binaries), that binary has the shortest orbital period. Then the mass ratio of the binary will reverse with mass transfer from the least massive component to the most massive after this special.
According to the study published in Monthly Notices of the Royal Astronomical Society, the researcher investigated the evolutionary stage of V375 Cassiopeia (V375 Cas), a massive binary and contains two B-type components.
They analyzed the light curves of the V375 Cas and found that the V375 Cas must undergo late mass transfer from the A case from the less massive to the more massive component.
Meanwhile, according to statistics, these massive semi-detached binaries have a third body with different periods. From the HR diagram, the components of the massive binaries are nearly the main sequence stars, and the evolutionary age of the secondary component is greater than that of the primary for V375 Cas. “V375 Cas is a hierarchical triple system where a massive main-sequence star accompanies a massive semi-detached mass transfer binary based on third-light estimation,” LI said.
The researchers also discovered two massive close binaries with twin components in M31. M31 is the closest spiral galaxy to the Milky Way and the largest galaxy in the Local Group, and its structure and metallicity are very close to those of the Milky Way.
The photometric solutions are carried out with the WD method from 437 eclipsing binaries, and two twin binaries have been found. One system is a contact binary with a mass ratio of 0.974, and the other system is a semi-detached binary with a mass ratio of 0.924. This result suggests that massive twin binaries are rare in M31.
Based on the study of the changes in orbital period by the OC diagrams and the configurations of the binaries, the researchers found that these two massive twin binaries are at different evolutionary stages with similar mass ratios (close to unity ). The double-contact binary is about to enter the critical shortest period evolutionary phase with rapid mass transfer. The semi-detached binary has gone through this stage of evolution and fails to form a contact binary during the orbit-decreasing phase with the mass transfer of case A.
These findings were published in The Astrophysical Journal.
These two works indicate that the evolution of massive binaries is equally possible in the Milky Way and M31, and these binaries at a particular stage create an ideal test bed of evolutionary models of massive binaries.