12 massive mass transfer binary stars have been found in the Andromeda galaxy

Recently, Li Fuxing, a doctoral student of the Binary and Variable Star Research Group of the Yunnan Astronomical Observatory of the Chinese Academy of Sciences, and Qian Shengbang, a researcher, have made new progress in the research of double stars in the Andromeda Galaxy (M31). The work used international sky survey data to systematically analyze the massive binary stars in the Andromeda galaxy for the first time, and found 12 secondary stars (small-mass stars) with Roche lobes from 437 binary system, revealing the transfer of matter from the secondary star to the massive host star in these systems, and also indicating that the evolution process of the binary stars in the Andromeda galaxy is similar to that in the Milky Way. The results were published online on April 8 in The Astronomical Journal, an international astronomical journal.

M31 is the closest spiral galaxy to the Milky Way and the largest galaxy in the home group. Its structural characteristics and metal abundance are very close to those of the Milky Way. The International Sky Survey has found a batch of binary stars in M31. Because M31 is relatively far away from humans (about 2.45 million light-years), most of the binary stars found on these surveys are massive binary stars, and only a small number of binary stars have undergone de-orbit analysis to determine the distance of M31. Other binary stars have hardly been analyzed or studied. Are there semi-contiguous and contiguous binary stars in M31 that are similar to those in the Milky Way? Are their structural characteristics and evolutionary states the same as those of massive binary stars in the Milky Way? These issues need to be further studied.

Figure 1 Light curve (luminance change curve over time) of some semi-contiguous binary stars in M31. In the figure, the pink square represents the V band, the black circle represents the B band, and the blue line and the red line represent the theoretically calculated two-color light change curve. The observed and theoretically calculated residuals are shown in a small box below the light curve.

The work used the sky survey observation data of the 2.5-meter telescope on the island of La Palma in Spain to analyze 437 binary star systems, and to study the metering and de-orbiting of some high-precision light curves (as shown in Figure 1), and to find their basic metering parameters. The researchers found that the secondary stars of the 12 binary stars were filled with Roche lobes, and the primary stars were separated from the Roche lobes, revealing that they were massive semi-contiguous binary stars, and that there was a transfer of material from the secondary star to the massive primary star in the system. The researchers also found that there may be a correlation between the host fullness of these binary stars and the mass ratio of the system, further supporting that they have undergone a mass ratio reversal and are in a slow stage of material exchange evolution. In addition , the temperature distribution of the primary and secondary stars of these binary systems is similar to that of semi-contiguous binary stars in the Milky Way. These findings reveal similarities in the evolution of binary stars in the Andromeda Galaxy to those in the Milky Way, and are of great value for exploring the evolution of material exchanges between massive binary stars.

This work has been funded by the National Natural Science Foundation of China. (Source: Yunnan Astronomical Observatory, Chinese Academy of Sciences)

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