B Stars

B stars are hot stars defined by the presence of hydrogen (H) and neutral helium (HeI) in the optical spectra. H line strength increases over the B star subclasses while HeI decreases. There are a wide variety of sub-types, as B stars occur over a wide range of luminosity, many have companion stars, and many have circumstellar material.

Other spectral features may include CaII, CII, CIII, NII, NIII, OII, SiII, SiIV, and MgII.

Be stars are defined as B stars having at least one of the hydrogen Balmer lines in emission at some time. These stars are rapid rotators, and a circumstellar shell and/or disk of gas is present. The circumstellar material may be due to mass loss or due to accretion from an evolved companion star. They are variable in both brightness and spectra. Spectra of Be stars show broad HeI absorption, and complex hydrogen Balmer line profiles that show emission out of the absorption cores.. A sub-class of the Be stars are the shell stars, which are Be stars oriented so that we see a circumstellar disk edge-on. The shell stars have spectra that show Balmer emission with sharp absorption cores, narrow absorption lines of ionized metals, and broad HeI absorption. Be stars are common, click here for a short catalog of selected Be and shell stars.