Helium-weak star


Helium-weak stars are chemically peculiar stars which have a weak helium lines for their spectral type. Their helium lines place them in a later spectral type than their hydrogen lines.

Helium-weak star

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 thought to be responsible for both types of chemical peculiarity.
This is a non-extensive list of helium-weak stars.
Star NameConstellationApparent Magnitude ClassNotes
20 Eridani Eridanus5.23B8/9 IIIα2 CVn variable
30 CapricorniCapricornus5.38B5 II/III
θ HydriHydrus5.50B8 III/IVSuspected Binary;
22 Eridani Eridanus5.53B9 IIIpSi α2 CVn variable
HD 74196Vela5.61B7 VnPart of IC 2391
HD 28843 Eridanus5.81B9 IIISX Arietis variable
12 Canis Majoris Canis Major6.08B7 II/IIISX Arietis variable
HD 34797 Lepus6.54B7 Vpα2 CVn variable; binary
HD 35456Orion6.95B9 II/IIIBinary

Helium-strong star

A related class of stars have anomalously strong helium lines in their spectra, and are known as helium-strong stars. These are the more massive stars with classes of B1 to B3, compared to the helium-weak stars with classes of B5 to B9. The following are examples:
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.