Researchers study the statistical properties of early stars derived from LAMOST DR8

Researchers led by Ph.D. Can­di­date Guo Yan­jun from the Yun­nan Obser­va­to­ries of the Chi­nese Acad­e­my of Sci­ences (CAS) have stud­ied the depen­dence of the intrin­sic bina­ry frac­tion on the inferred stel­lar effec­tive tem­per­a­ture, metal­lic­i­ty and pro­ject­ed rota­tion rate.

The study was pub­lished in Astron­o­my & Astro­physics on Novem­ber 4th. It was based on the intrin­sic bina­ry frac­tion of the LAMOST DR8 of mas­sive stars. Researchers used the Medi­um Res­o­lu­tion Spec­tra (MRS) data­base to col­lect opti­cal spec­tra of 886 ear­ly star types, each with more than six observations.

Ear­ly-type stars, with a spec­tral clas­si­fi­ca­tion range from O‑type to A‑type, are mas­sive and have high effec­tive tem­per­a­tures. They con­tribute to the reion­iza­tion of the uni­verse and can enrich metal­lic­i­ty in the galac­tic envi­ron­ment. Most ear­ly-type stars occur in bina­ries and are like­ly to evolve into com­pact bina­ry sys­tems such as bina­ry black holes, bina­ry neu­tron stars, or bina­ry stars and black holes.

Sta­tis­ti­cal prop­er­ties of ear­ly-type mas­sive stars such as Data such as intrin­sic bina­ry frac­tion, orbital peri­od dis­tri­b­u­tion, and mass ratio are com­mon­ly used as essen­tial inputs for bina­ry pop­u­la­tion syn­the­sis mod­els and are impor­tant trac­ers to study star for­ma­tion. How­ev­er, pre­vi­ous work was often lim­it­ed by a small sam­ple of obser­va­tions or incon­sis­tent data from dif­fer­ent sources.

In this study, researchers obtained obser­va­tions for 886 ear­ly stars from the data­base, and each tar­get star has more than six spec­tra. Based on the inferred stel­lar effec­tive tem­per­a­ture, metal­lic­i­ty, and pro­ject­ed rota­tion rate, researchers divid­ed the sam­ple into sub­groups. Radi­al veloc­i­ty mea­sure­ments of each tar­get star were col­lect­ed from a pre­vi­ous study led by Guo, and a series of Monte Car­lo sim­u­la­tions were applied to the mea­sure­ments to cor­rect for pos­si­ble bias­es in the obser­va­tion in the sample.

The researchers found that the intrin­sic bina­ry frac­tion in the sam­ple showed an increas­ing trend toward a pop­u­la­tion with a high­er effec­tive tem­per­a­ture. The bina­ry frac­tion could reach up to ~76% for O and B type stars, while it would drop to 48% for B and A type stars. A sim­i­lar trend was not­ed in the rela­tion­ship between intrin­sic bina­ry con­tent and metal­lic­i­ty, where the ratio reached ～72% for met­al-rich stars and dete­ri­o­rat­ed to 44% for met­al-poor stars in the sample.

These results are fur­ther applied to evo­lu­tion­ary mod­els to con­strain the for­ma­tion process of mas­sive bina­ry stars and pro­vide insights into com­pact bina­ry star for­ma­tion scenarios.