LAMOST found candidates for 734 failed evolutionary stars

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Brown dwarf art figure (Image: scienceabc)

Recently, using the 7th batch of low-resolution spectral data (LAMOST DR7) released by the Guo Shoujing telescope, Dr. Wang Youfen of the National Astronomical Observatory of the Chinese Academy of Sciences and researcher Luo Ali and others found 734 extremely cold dwarf stars, which are candidates for brown dwarfs. The research results were published in Astronomy and Astrophysics.

Extremely cold dwarfs, especially brown dwarfs, are substellar objects with no stable nuclear fusion in the core, or a star that has failed to evolve, and are also the frontier research field that has emerged in recent decades, they are small in mass, red in color, dark in brightness, very difficult to observe, and extremely high requirements for observation equipment.

“The sample we found is the largest sample of an extremely cold dwarf currently available with uniform spectral data and complete parametric information.” Wang Youfen told China Science Daily, “This result demonstrates LAMOST’s observation capabilities at the dark end to a certain extent, confirming the possibility of the large-aperture spectral survey telescope studying extremely cold dwarfs.” ”

Early on , in stellar spectroscopic classification systems , M-type stars were the coldest stars. Later, after M-type stars, astronomers worked on and defined new classifications of spectral types L, T, and Y to describe the spectral types of extremely cold dwarfs. Extremely cold dwarfs are collective terms for spectral late M ( M7 – M9 ) and L , T , and Y dwarfs whose absolute magnitude is very faint and are located at the lower right of the color-absolute magnitude map ( figurine ) .

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The position of the extremely cold dwarf sample on the color-absolute magnitude chart, with black being the extremely cold dwarf sample data and cyan being the contrast data. (Courtesy of the interviewee)

In terms of spectroscopy, the extremely cold dwarfs of the late M and early L may be either brown dwarfs or ordinary low-mass stars, depending on their own mass. Extremely cold dwarfs after the middle and late L type (L3) are brown dwarfs if they have masses between 13 and 75 times the mass of Jupiter.

Wang Youfen introduced that brown dwarfs are bridges linking stars and planets, and play a very important role in the formation history of the Milky Way, the initial mass function, and the study of hot planetary atmospheres. Extremely cold dwarfs are important in studying the chemical reactions and physical processes inside the stars at the junction of stars and brown dwarfs because they are so dim that they are easier to observe and find very small-mass terrestrial planets around them, so they are also ideal candidates for the search for terrestrial planets (rocky planets).

The research team screened more than 10,000 late M-type stars from more than 700,000 M-type stars in the LAMOST DR7 data, and then manually examined and compared them to select 734 extremely cold dwarfs with kinematic age of about 300 million years and kinematic characteristics and metal abundance similar to those of the Milky Way Disc Star.

“The spectral information of two-thirds of the extremely cold dwarfs in this sample is obtained for the first time, and the spectral data is well consistent, so this is a very rare large sample of extremely cold dwarfs with complete parameter information up to now.” Wang Youfen said, “These extremely cold dwarfs are very close to us, 80% of the member stars are within 300 light years, the farthest is only 1174 light years; their observations are the darkest magnitude of 19.2, the average is 16.2 magnitudes; the effective temperature distribution is between 2600K and 3300K.” These extremely cold dwarfs are all candidates for brown dwarfs, of which 77 poles have obvious lithium absorption lines, and the possibility that they are brown dwarfs is very high. ”

The researchers also found in the sample that 6 of the wide-ranging binary stars were discovered for the first time, and their companions could theoretically be less massive, so their companions are most likely brown dwarfs.

“This sample has important scientific application value for the properties and evolution of extremely cold dwarfs, especially brown dwarfs, which are very difficult to observe.” “In the near future, with the accumulation of LAMOST spectral data and the launch of the Chinese Space Telescope (CSST), we may be able to detect more distant brown dwarfs, bringing more opportunities for the study of the relatively vacant brown dwarf formation mechanism and internal properties in the field of stellar physics research,” Luo said. (Source: China Science Daily Shen Chunlei)

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