Recently, a series of studies about massive binaries were published in Monthly Notices of the Royal Astronomical Society (MNRAS) and The Astrophysical Journal (ApJ). In these works, PhD student LI Fuxing, Prof. QIAN Shengbang, et al., from Yunnan Observatories, investigate the formation and evolution of the massive binaries in the Milky Way and Andromeda Galaxy (M31) respectively.

Massive binary contains at least an early-type star whose spectral type is O, B-type. These binaries have high-energy radiation such as X-rays, and they perhaps create neutron stars or black holes. This proves a valuable chance to study the special astrophysical phenomenon.The progenitors of these semidetached binaries are the detached binaries where the original more massive components evolve faster and fill their critical Roche lobes first, and then transfer mass to their companions with the case A evolution.It is significant to study twin binaries and to reveal the formation and evolution of massive binaries.

During this process, the orbital period of the system will be decreased and the mass ratio will be increased. When the system evolves to the critical state where the mass ratio is equal to 1 (twin binaries), this binary has the shortest orbital period. Then the mass ratio of binary will be reversed with mass transfer from the less-massive component to the more-massive one after this special stage.

The work in MNRAS studies the evolution stage of V375 Cassiopeia (V375 Cas), which is a massive binary and contains two components of B-type. Researchers analyzed the light curves of V375 Cas again with the high-precision continuous data from Transiting Exoplanet Survey Satellite (TESS). They performed the orbital period changes for the first time by the O-C diagram with the eclipse minima spanning 122 yr, the data from DASCH (the surveys of the Digital Access to a Sky Century at Harvard), KWS (the Kamogata/Kiso/Kyoto Wide-field Survey) and TESS et al. They found that V375 Cas should undergo a late case A mass transfer from the less-massive component to the more-massive one.

Meanwhile, according to the statistics, those massive semidetached binaries have a third body with different periods in the paper. From the H-R diagram, it was found that the components of the massive binaries almost are the main-sequence stars, and the evolutionary age of the secondary component is larger than that of the primary for V375 Cas. Researchers also found that V375 Cas is a hierarchical triple system where a massive main-sequence star accompanies a massive semidetached mass-transfer binary based on the estimation of the third light.

The work in ApJ discovers 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, its structure and metallicity are very close to that of the Milky Way. The light curves were observed by the 2.5 m Issac Newton Telescope in Spain and obtained from the DIRECT survey project. The photometric solutions are performed with the W-D method from 437 eclipsing binaries, and two twin binaries have been found. One system is contact binary with a mass ratio of 0.974, and the other system is semidetached binary with a mass ratio of 0.924. This result hints the massive twin binaries are rare in M31.

Based on the study of the orbital period changes by the O-C diagrams and configurations of binaries, researchers found that these two massive twin binaries are at different evolutionary stages with similar mass ratios (close to unity). The twin contact binary is about to enter the critical evolutionary stage of the shortest period with rapid mass transfer. The semidetached binary has experienced that evolution stage and fails to form a contact binary during the orbit decreasing phase with case A mass transfer.

These two works indicate that the evolution of massive binaries is possible same in the Milky Way and M31, and these binaries at a special stage create an ideal testbed of evolutionary models of massive binaries.

Contact:
LI Fuxing,
Yunnan Observatories, CAS
Email: lfx@ynao.ac.cn