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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