There are stars that do not fit into any of the spectral classes, call them peculiar.Often they are normal stars at a certain evolutionary stage.Stars with peculiar spectra have different features of the chemical composition of which strengthen or weaken the spectral lines of a number of elements.Such stars are not typical for the nearest neighborhood of the sun, such as metal poor stars in globular clusters or the galactic halo.
Most stars belong to the main sequence, referred to as normal, such stars are the sun.Depending on what stage of evolutionary development is the star, it is referred to the normal star, the dwarfs or giant stars.
Star can be a red giant at the time of formation, and
in the later stages of its development.At the very early stage of development due to the star emits gravitational energy released during its compression.This continues until the fusion reaction starts.After the hydrogen burning stars converge towards the main sequence, moving to red giants and supergiants.
For giant stars are characterized by a relatively low temperature - about 5000 K. They have a very large radius and a great luminosity, radiation peaks and the red and infrared part of the spectrum, for this reason they are often called red giants.
dwarf stars are separated by no more subspecies: white dwarfs, red, black, brown and subkorichnevye.Bylymi dwarfs are stars that have passed the stage of its evolution.Their weight does not exceed 1.4 solar, they lack their own sources of fusion energy.The diameter of the white dwarf can be hundreds of times smaller than the sun, and the density - a million times greater than the density of water.
Red dwarfs are significantly different from other stars.It is small and relatively cool main sequence stars with spectral type M or K. Their diameter does not exceed one third of the sun, the lower limit for the mass of the stars of this type is 0.08 solar.
a black dwarf - is cooled without emitting in the visible range of white dwarfs.They are the final stage in the evolution of white dwarfs.Their mass is limited to the top 1.4 solar masses.
Brown dwarfs are a substellar objects whose masses are in the range of 5-75 Jupiter masses and a diameter approximately equal to the diameter of the planet.In contrast to the main sequence stars in their depths there is no reaction of thermonuclear fusion.Subkorichnevye dwarfs - a cold education, their mass is less than that of brown dwarfs.Some astronomers believe their planets.
- astrotime.ru, Forms stars