Saturday, January 14, 2012

Spectral Types of Stars


Spectral Types of Stars
Astronomers categorize stars according to the the characteristics of the light that the stars emit, which are related to the stars’ temperatures. O stars are the hottest stars, and M stars are the coolest. Our Sun is a G star.
Spectral Class
Effective Temperature
Star Color
Principal Characteristics

O
25,000 K
Blue star
This stage is characterized by lines of helium, oxygen, and nitrogen in the spectrum of the photosphere. O stars are extremely hot, very bright stars that emit large amounts of ultraviolet radiation.
B
11,000 K -
25,000 K
White-blue star
In this group the lines of helium in the spectrum reach a maximum intensity and then fade. The intensity of the hydrogen lines regularly increases in all the subdivisions of stage B. Type B stars are typically represented by the star Epsilon Orionis.
A
7500 K - 11,000 K
White star
This group comprises the so-called hydrogen stars. The spectra of these stars is dominated by absorption lines of hydrogen. Sirius, the Dog star, is a typical type A star.
F
6000 K - 7500 K
Yellow-white star
This group is composed of stars characterized by an elevated intensity of the H and K lines of calcium and of lines characteristic of hydrogen. A notable star in this category is Delta Aquilae.
G
5000 K - 6000 K
Yellow, solar star
This group is composed of stars with prominent H and K calcium lines and less prominent hydrogen lines. The spectra of numerous metals, in particular iron, are also present. The Sun belongs to this group, and therefore G stars are frequently called solar stars.
K
3500 K - 5000 K
Orange-yellow star
This group comprises stars having strong calcium lines and lines indicating the presence of other metals in their spectra.The violet light of class K stars is less intense
than the stars' red light. This group is typically represented by Arcturus.
M
3500 K
Red star
This group is composed of stars whose spectra are dominated by bands resulting from the presence of metallic-oxide molecules, notably those of titanium oxide. The violet end of the spectra is less intense than that of K stars. The star Orionis is typical of this group.


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