12/30/2023 0 Comments A type main sequence star![]() Objects known as B stars are distinct from Be stars in having unusual neutral or low ionization emission lines that are considered to have ' forbidden mechanisms', something denoted by the use of the square brackets. Be stars are generally thought to feature unusually strong stellar winds, high surface temperatures, and significant attrition of stellar mass as the objects rotate at a curiously rapid rate, all of this in contrast to many other main-sequence star types. Spectral objects known as "Be stars" are massive yet non- supergiant entities that notably have, or had at some time, 1 or more Balmer lines in emission, with the hydrogen-related electromagnetic radiation series projected out by the stars being of particular scientific interest. Many B-type stars have a rapid rate of rotation, with an equatorial rotation velocity of about 200 km/s. This results in a steady mixing of the hydrogen fuel with the helium byproduct of the nuclear fusion. Because the CNO cycle is very temperature sensitive, the energy generation is heavily concentrated at the center of the star, which results in a convection zone about the core. The energy generation in main-sequence B-type stars comes from the CNO cycle of thermonuclear fusion. ![]() They have a higher mass loss rate than smaller stars such as the Sun, and their stellar wind has velocities of about 3,000 km/s. Type-B stars do not have a corona and lack a convection zone in their outer atmosphere. Properties Properties of typical B-type main-sequence stars Spectral The lines of ionized silicon are used to determine the sub-class of the B-type stars, while magnesium lines are used to distinguish between the temperature classes. The Balmer series of hydrogen lines grows stronger through the B class, then peak at type A2. Thus, in the MK Classification system, the spectral class B0 has the line at wavelength 439 nm being stronger than the line at 420 nm. Subsequent catalogues of stellar spectra classified the stars based on the strengths of absorption lines at specific frequencies, or by comparing the strengths of different lines. Likewise, A0 stars also show weak lines of non-ionized helium. Later, however, more refined spectra showed lines of ionized helium for stars of type B0. Thus B2 is 1/5 of the way from type B (or B0) to type A. All of the spectral classes, including the B type, were subdivided with a numerical suffix that indicated the degree to which they approached the next classification. The definition of type B-type stars was the presence of non- ionized helium lines with the absence of singly ionized helium in the blue-violet portion of the spectrum. This class of stars was introduced with the Harvard sequence of stellar spectra and published in the Revised Harvard photometry catalogue. Their spectra have strong neutral helium absorption lines, which are most prominent at the B2 subclass, and moderately strong hydrogen lines. B-type stars are extremely luminous and blue. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. A B-type main-sequence star (B V) is a main-sequence ( hydrogen-burning) star of spectral type B and luminosity class V.
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