Helium-weak stars are mid-to-late B-class stars with weaker than normal spectral lines of neutral helium, compared to normal stars with similar hydrogen line strengths. These are considered to be an extension of the Ap/Bp chemically-peculiar stars with slightly hotter temperatures. They often show similar increased abundances of heavy elements. The mechanism of atmospheric stratification of elements is though to be responsible for both types of chemical peculiarity.[4][5]
This is a non-extensive list of helium-weak stars.[6][7]
A related class of stars have anomalously strong helium lines in their spectra, and are known as helium-strong stars.[1] These are the more massive stars with classes of B1 to B3, compared to the helium-weak stars with classes of B5 to B9.[8] The following are examples:
V761 Centauri (a Centauri) is well-known for both the variability of its brightness and of its helium spectral lines. Stars of this type are referred to as helium-variable. This is thought to occur when one hemisphere of the star's atmosphere is helium-weak and one is helium-strong.[9]
^Alonso, M. S.; López-García, Z.; Malaroda, S.; Leone, F. (2003). "Elemental abundance studies of CP stars. The helium-weak stars HD 19400, HD 34797 and HD 35456". Astronomy and Astrophysics. 402: 331. Bibcode:2003A&A...402..331A. doi:10.1051/0004-6361:20030222.
