SIMBAD references

Algol-type binaries (Algols) have aroused extensive interests due to the idiosyncratic evolutionary stages of both components. To better understand the evolutionary properties of such characteristic population, we collected mostly double-lined samples and performed systematic work concentrated on their physical constraints. It is found that orbital period cut-off for the OB and AF type Algols are P(OB) > 0.482 d, P(AF) >0.358 d; constraints on mean density and surface gravity of the secondary components are _2(OB) < 0.144 ρ_☉, _2(AF) < 0.26 ρ_☉, log g₂(OB) < 4.719 cgs, and log g₂(AF) < 4.517 cgs. Limitations of a(OB) > 3.48 R_☉ and a(AF) > 2.29 R_☉ have been deduced from the a-P relation. Moreover, statistical analysis of secular period changes reveal that Algols with higher f₁ and relevant shorter period generally show weak period change. It hints that there is some connections between f₁ and orbital evolution. Systems with lower f₁ have the chance to evolve from classic Algols to SD2-type near contact binaries (NCBs); systems with higher f₁ obey the evolutionary channel from SD2-type NCBs to CBs. However, it seems that SD2-type NCBs could not evolve towards classic Algols. As a natural lab, Algols are producing peculiar stellar experimental samples via complicated astrophysical processes, which will enhance our understanding on the physical properties and evolution of such binary populations.