Looking for the genuine tiny red beasts in the Milky Way


 

There is a special group of tiny red beasts wandering across the Milky Way galaxy. They are red subdwarf stars that are aborigines of the Milky Way and considered to be born in the galactic halo and thick disk.


Prof. Luo Ali from National Astronomical Observatories of Chinese Academy of Sciences (NAOC). Prof. Luo's team has been making in-depth research on M subdwarfs said, learning more about these M subdwarfs can help us know the history of our galaxy. They are indeed quite rare in the solar neighborhood, but people usually mixed them with some metal-poor, disk-born red dwarfs.


The research team studied the properties of thousands of subdwarfs to understand the intrinsic difference between these scarce M subdwarfs and the normal M dwarfs which are the most numerous stellar members in the Milky Way. Their study was published in The Astrophysical Journal.


Zhang Shuo, the first author of the study said, we have revised the spectroscopic classification system and measured the atmospheric parameters of all the dwarf/subdwarf samples. The results show that the new system behaves better on finding the tiny red beasts, which are the genuine subdwarfs.


The researchers studied the effects of the revision in the classification system that was applied to the spectroscopic subdwarf samples selected from LAMOST and SDSS. They found that the genuine subdwarfs identified by luminosity and motion are the ones with the lowest metal abundances, and also have the highest gravity, which was not considered a characteristic feature of subdwarf stars.


Zhang Shuo said, for decades, people have collectively referred to the real subdwarfs and a group of metal-poor dwarfs as subdwarfs based on some specific spectral features, but these misclassified stellar objects behave like classical disk dwarfs on all aspects. We found that gravity value is a great criterion to separate them from the genuine subdwarfs.


Prof. Luo said, the largest sample of M subdwarf stars we built ever had helped us to make this important discovery. More importantly, kinematic and chemical analysis shows that the sample contains a mix of objects belonging to various stellar populations and having different origins, which deserves further study.

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