Download Star Classes

Star Classes
Los Cumbres Observatory
Red Star, Blue Star
Compared to a red star, a blue star always has
A. more mass.
B. larger radius.
C. hotter temperature.
D. all of the above.
Luminosity vs. Temperature
• Astronomers plot the
luminosity of a star
compared to its
temperature.
-20
-15
Abs. Magnitude
-10
-5
0
Sun
5
10
– Absolute magnitude for
luminosity
15
20
O B A F G K M
Spectral Type
– Spectral type/class for
temperature
Hertzsprung-Russell Diagram
• The chart of luminosity
vs. temperature is called
the Hertzsprung-Russell
diagram.
• This is the H-R diagram
for hundreds of nearby
stars.
Main Sequence
• Most stars are on a line
called the main sequence.
-20
-15
– Hot stars brighter
Abs. Magnitude
-10
-5
0
Sirius
5
1 solar
radius
10
15
20
O B A F G K M
Spectral Type
• The size is related to
temperature and luminosity.
– Hot = large radius
– Medium = medium radius
– Cool = small radius
Giants
• Stars that are brighter than
the main sequence are
giants or supergiants.
-20
-15
Abs. Magnitude
-10 Rigel
-5
0
5
supergiants Betelgeuse
giants
Aldebaran
Capella
• Betelgeuse is a red
supergiant.
10
15
20
– Large size
– More luminosity
O B A F G K M
Spectral Type
– Radius 1000 R
Dwarfs
• Stars that are dimmer than
the main sequence are
dwarfs.
-20
-15
Abs. Magnitude
-10
– Small size
– Less luminosity
-5
0
5
10
15
20
white
dwarfs
O B A F G K M
Spectral Type
• Red dwarfs are on the
main sequence.
• White dwarfs are hot and
small.
Spectroscopic Parallax
• Parallax measurements of close stars determine the
luminosity for placement on the H-R diagram.
– Distant stars similar to close ones
1.
2.
3.
4.
Determine surface temp and spectral class of star.
Place the star on the HR diagram where it should go.
Read off the absolute luminosity from the diagram.
Measure apparent luminosity and calculate distance.