Chapter 16--Properties of Stars
Chapter 16--Properties of Stars
Chapter 16--Properties of Stars
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
When classifying a star, astronomers generally report<br />
both the star’s spectral type and a luminosity class that<br />
describes the region <strong>of</strong> the H–R diagram in which the star<br />
falls. Table <strong>16</strong>.2 summarizes the luminosity classes: Luminosity<br />
class I represents supergiants, luminosity class III<br />
represents giants, luminosity class V represents main-<br />
luminosity (solar units)<br />
10 6<br />
10 5<br />
10 4<br />
10 3<br />
10 2<br />
10<br />
1<br />
0.1<br />
10 2<br />
10 3<br />
10 4<br />
10 5<br />
60M Sun<br />
10 Solar Radii<br />
Lifetime<br />
10 7 yrs<br />
1 Solar Radius<br />
30M Sun<br />
0.1 Solar Radius<br />
10 2 Solar Radius<br />
10 3 Solar Radius<br />
Sirius B<br />
increasing temperature<br />
10 2 Solar Radii<br />
Centauri<br />
Spica<br />
10MSun MAIN<br />
Lifetime<br />
10 8 yrs<br />
Bellatrix<br />
6MSun Achernar<br />
Lifetime<br />
10 9 yrs<br />
Figure <strong>16</strong>.10 An H–R diagram, one <strong>of</strong> astronomy’s most important tools, shows how the surface temperatures<br />
<strong>of</strong> stars (plotted along the horizontal axis) relate to their luminosities (plotted along the vertical<br />
axis). Several <strong>of</strong> the brightest stars in the sky are plotted here, along with a few <strong>of</strong> those closest to<br />
Earth. They are not drawn to scale—the diagonal lines, labeled in solar radii, indicate how large they are<br />
compared to the Sun. The lifetime and mass labels apply only to main-sequence stars (see Figure <strong>16</strong>.11).<br />
(Star positions on this diagram are based on data from the Hipparcos satellite.)<br />
Rigel<br />
Sirius<br />
Deneb<br />
SEQUENCE<br />
sequence stars, and luminosity classes II and IV are intermediate<br />
to the others. For example, the complete spectral<br />
classification <strong>of</strong> our Sun is G2 V. The G2 spectral type means<br />
it is yellow in color, and the luminosity class V means it is<br />
a main-sequence star. Betelgeuse is M2 I, making it a red<br />
supergiant. Proxima Centauri is M5 V—similar in color and<br />
3MSun Vega<br />
Procyon B<br />
30,000 10,000<br />
Sirius<br />
Altair<br />
Lifetime<br />
10 10 yrs<br />
WHITE<br />
DWARFS<br />
10 3 Solar Radii<br />
SUPERGIANTS<br />
Canopus<br />
Polaris<br />
Arcturus<br />
Procyon<br />
1.5MSun GIANTS<br />
Pollux<br />
Aldebaran<br />
Lifetime<br />
10 11 Sun<br />
Centauri A<br />
1MSun Centauri B<br />
Ceti Eridani<br />
61 Cygni A<br />
61 Cygni B<br />
Lacaille 9352<br />
0.3MSun Gliese 725 A<br />
Gliese 725 B<br />
yrs<br />
Barnard’s Star 0.1MSun Ross 128<br />
Wolf 359<br />
Proxima Centauri<br />
DX Cancri<br />
Betelgeuse<br />
Antares<br />
6,000 3,000<br />
surface temperature (Kelvin) decreasing temperature<br />
chapter <strong>16</strong> • <strong>Properties</strong> <strong>of</strong> <strong>Stars</strong> 533