Glossary term: B-type Star

Also known as B star or B-star

Description: A star with spectral type "B". Astronomers identify B-type stars by the presence of neutral helium lines along with hydrogen lines in their spectra. They have typical (effective) temperatures between around 10,000 kelvins (K) to 30,000 K. Compared to other stars, they appear bluish white to human eyes unless interstellar or atmospheric reddening is important. Examples of B-type stars include Regulus in Leo, Rigel in Orion, and Spica in Virgo.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Diagrams

A smooth line declining at longer wavelengths with a few sharp dips.

Spectrum of a B-type star

Caption: The spectrum of the B-type star HD 258982. The colour of the line between 400 nm and 700 nm roughly corresponds to the colour the human eye would see light of that wavelength. Below 400 nm and above 700 nm, where the human eye can see little to no light, the lines are coloured blue and red respectively. The black lines show spectral absorption lines caused by atoms and ions of different elements in the star’s atmosphere. These atoms and ions absorb at specific wavelengths, causing sharp, dark lines in the spectra. How strong these lines are depends on the temperature of the star’s atmosphere. Two stars made from the same mix of elements could have spectra with vastly different sets of lines in their spectra if they have different temperatures in their atmospheres. For B-type stars the most important lines are caused by helium atoms. These lines are strongest in B-type stars and weaker in hotter and cooler types. Lines from hydrogen atoms are also present but are not as strong as in cooler A-type stars.
Credit: IAU OAE/SDSS/Niall Deacon

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