The Effects Of Convective Overshooting On Naked Helium Stars

Compared with normal stars, the helium fraction of naked helium stars is very copi-ous (up to 98%) and the hydrogen is very scarce (approaching zero). Naked helium stars are considered to be helium core burning objects with extremely thin hydrogen envelopes. Systematic investigation of the formation and evolution of the naked helium stars can help us understand a great many of hydrogen-deficient objects. All that acknowledged, both subdwarf B stars and Wolf-Rayet stars have relations with naked helium stars in the field of astrophysics.We already know that the convection and convective overshooting greatly affect the evolutionary properties of normal stars. Using PPE stellar evolution code, we investigate the effects of the convective overshooting on naked helium stars. We find that a larger value of overshooting parameter δov results in a larger convective core, which means that much more fuel could be sent to the center nuclear region, the nuclear energy generation rate is enhanced which increases luminosity. Moreover, it prolongs the lifetimes of naked helium stars on helium main sequence. Naked helium stars have a little of hydrogen (and there is no hydrogen in our models), their evolutionary tracks extend towards higher ef-fective temperatures. A larger value of overshooting parameter δov makes higher effective temperatures and widens the helium main sequence phase of naked helium stars.In addition, for naked helium stars with masses lower than about 0.8 M(?), they hardly become giant stars as a result of weak burning shell. However, the naked helium stars with masses between about 0.8 Mo and 1.1 Mo can evolve into giant branch phases, and finally become carbon oxygen white dwarfs. For relatively massive naked helium stars (> 1.1 M(?)), they cannot become carbon oxygen white dwarfs.