The following table is a summary of the main characteristics of
stars, and their relative abundance within our galaxy.
The parameters of mass, radius and luminosity of stars are expressed in relation
with the Sun.
These parameters are only relevant for main sequence stars, not for supergiant
ones.
As the spectral class is only based upon the surface temperature of a star,
this table can only define one point on the Hertzprung-Russel
diagram.
The W class corresponds to the Wolf-Rayet stars.
| Spectral class |
Surface temperature (degrees K) |
Mass | Radius | Luminosity | Life time (million of years) |
Relative abundance (in %) |
|---|---|---|---|---|---|---|
| W | 50.000 | >40 | 20 | 1.000.000 | <1 | negligible |
| O5 | 40.000 | 32 | 18 | 600.000 | 1 | 0.00002 |
| B0 | 28.000 | 16 | 7.4 | 16.000 | 10 | |
| B5 | 15.500 | 6.5 | 3.8 | 600 | 100 | 0.1 |
| A0 | 9.900 | 3.2 | 2.5 | 60 | 500 | |
| A5 | 8.500 | 2.1 | 1.7 | 20 | 1.000 | 1 |
| F0 | 7.400 | 1.75 | 1.4 | 6 | 2.000 | |
| F5 | 6.600 | 1.25 | 1.2 | 3 | 4.000 | 3 |
| G0 | 6.000 | 1.06 | 1.1 | 1.3 | 10.000 | |
| G2 Sun | 5.800 | 1 | 1 | 1 | 12.000 | |
| G5 | 5.500 | 0.92 | 0.9 | 0.8 | 15.000 | 9 |
| K0 | 4.900 | 0.80 | 0.8 | 0.4 | 20.000 (1) | |
| K5 | 4.100 | 0.69 | 0.7 | 0.1 | 30.000 | 14 |
| M0 | 3.500 | 0.48 | 0.6 | 0.02 | 75.000 | |
| M5 | 2.800 | 0.20 | 0.3 | 0.001 | 200.000 | 73 |
| C | ~2500 | ~5/10 | (2) | (2) | 0.1 | negligible |
| S | ~2000 | ~5/10 | (2) | (2) | 0.1 | negligible |
(1) The estimated lifetime of the universe is less than 20 billion years, so no K or M class star is yet dead.
(2) These stars are often variable. They can sometimes get up to 1000 solar radii. Similarly, their luminosity can vary between 30 and 30,000 times the Solar luminosity.
The majority of stars are small stars, in the classes M and K.
Giant and supergiant stars are very rare, and their short lifetimes emphasizes
this rarity.
Besides these physical features, we must notice spectral characteristics : spectra of stars in the same class show the same radiation lines. In fact, two stars with the same spectral type are quite similar in physical features.
| Class | Prominent lines | Other lines |
|---|---|---|
| W | Ionized helium, hydrogen | Carbon and Oxygen (class WC) Nitrogen (class WN) |
| O | Ionized Helium | Neutral helium, weak hydrogen lines |
| B | Neutral Helium | Hydrogen lines growing in B6 to B9 |
| A | Strong hydrogen lines in A0, decreasing towards A9 | ionized calcium lines stronger and stronger from A0 to A9 |
| F | Stronger ionized calcium lines | |
| G | Strong ionized calcium lines | Metals, specially iron |
| K | Strong neutral metals lines | CH and CN molecules |
| M | Absorption lines of titanium oxyde | Many metal lines |
| C | Neutral metals | Carbon |
| S | Neutral metals | Zirconium oxyde, Yttrium, Baryum |