Download LAB: Star Classification

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LAB: Star Classification
INTRODUCTION: Like most scientists, astronomers like to categorize the Universe
around them, and stars are no exception. Here’s how astronomers classify stars into
different groups; let’s learn a bit about star classification.
Stars are classified based on the spectral characteristic of the light it’s giving off. As you
probably know, the light we see with our eyes is actually a mixture of colors. You can
break them up into their different parts just like you can use a prism to break sunlight into
all the colors of a rainbow. The rainbow that we see is actually the spectrum produced by
the Sun, and it’s different for different stars depending on their temperature. A cooler star
will have a spectrum that has more red in it, while a hotter star will be shifted up towards
the blue end of the spectrum.
Astronomers classify stars by color using a series of letters: O, B, A, F, G, K and M. You
can remember the sequence with the handy mnemonic, “oh be a fine girl and kiss me”.
Under this classification, O stars are the hottest, and M stars are the coolest, with the
other letters coming in between. O stars are “blue”, A stars are “white”, G stars are
“yellow”, and M stars are red.
From Star Classification by Fraser Cain on February 4, 2009 http://www.universetoday.com/24633/star-classification/
OBJECTIVE: To identify the main characteristics used to classify stars, and the four
main types of stars. You will also become familiar with the use of the HertzsprungRussell diagram used for the classification of stars.
PROCEDURE:
1. Using the data from Table 1 and the blank Hertzsprung-Russell diagram provided,
plot the position of each star using its approximate temperature and luminosity.
Label each star’s name next to its data point on the chart.
2. Using the information provided in Table 2, and colored pencils, shade in each
temperature region of your Hertzsprung-Russell diagram with the correct star
color.
3. In bold letters, label the following regions of your Hertzsprung-Russell diagram:
Main Sequence, Giants, Supergiants, White Dwarfs.
4. Using the information provided in Table 3, label the spectral class in the
appropriate place on your Hertsprung-Russell diagram with the correct letter
based on the corresponding color.
Table 1 - Star Temperature and Luminosity
Star
Temperature
(ºC)
14,000
3,500
6,500
4,000
3,000
6,000
6,000
6,600
8,300
10,000
9,700
5,000
4,300
12,300
16,700
19,700
21,000
Rigel
Betelguese
Polaris
Aldebaran
Barnard’s Star
Alpha Centauri A
Sun
Procyon B
Sirius B
Sirius A
Vega
Tau Ceti
Alpha Centauri B
Regulus
Achernar
Spica
Beta Centauri
Luminosity
(compared to the Sun)
50,000
12,000
1,000
100
0.002
3
1
0.001
0.001
20
60
0.5
0.3
300
1,000
800
1,200
Table 2 - Star Temperature and Color
Star Temperature (ºC)
2,000 - 3,500
3,500 - 5,000
5,000 - 6,000
6,000 - 7,500
7,500 - 11,000
11,000 - 18,000
18,000 - 30,000
Star Color
Red
Orange
Yellow
White
Pale Blue-White
Blue-White
Blue
Table 3 - Spectral Class and Temperature
Spectral Class
O
B
A
F
G
K
M
Temperature (ºC)
over 24,000
11,000 - 24,000
7,500 - 11,000
6,000 - 7,500
5,000 - 6,000
3,500 - 5,000
2,000 - 3,500
Discussion Questions: Answer using data from the lab and in complete thoughts.
1. As a star changes color from red to blue, describe what happens to its surface
temperature?
2. What two properties are used to classify stars using the Hurtzsprung-Russell
diagram?
3. A main sequence star that is 10,000 times more luminous than the Sun most likely
has a temperature of:
4. A main sequence star that has a luminosity of 100 is most likely to be what color?
5. A white dwarf star with a temperature of of approximately 10,000 ºC would have
a luminosity of:
6. A massive star with a temperature of 20,00ºC and a luminosity of nearly
1,000,000 would be classified as what type of star?
7. What is the temperature, luminosity, and spectral class of the Sun?
8. What physical property must a star have that is low in temperature but very high
in luminosity?
9. What physical property must a star have that is high in temperature but very low
in luminosity?
Reading Comprehension Read the portion of the article on White Dwarfs below and
answer the following questions based on the reading. Use complete sentences
Hottest White Dwarf In Its Class
http://www.sciencedaily.com/releases/2008/12/081212081540.htm
ScienceDaily (Dec. 12, 2008) — Astronomy & Astrophysics is publishing observations of the white dwarf
KPD 0005+5106. The team who present these observations show that this white dwarf is among the hottest
stars known so far, with a temperature of 200,000º K at its surface.
Stars of intermediate mass (1-8 solar masses) terminate their life as an Earth-sized white dwarf after the
exhaustion of their nuclear fuel. During the transition from a nuclear-burning star to the white dwarf stage,
the star becomes very hot. Many such objects with surface temperatures around 100 000 Kelvin are known.
Theories of stellar evolution predict that the stars can be much hotter. However, the probability of catching
them in such an extremely hot state is low, because this phase is rather short-lived.
Since its discovery as a faint blue star in 1985, KPD 0005+5106 attracted much attention because
observations taken with ground-based telescopes suggested that this white dwarf is very hot. In addition, it
belongs to a particular class of rare white dwarfs whose atmospheres are dominated by helium. A detailed
analysis had led to the conclusion that KPD 0005+5106 has a temperature of 120 000 Kelvin, which made
Although theory predicted the existence of such hot white dwarfs, the star nevertheless represents a
challenge to our concepts of stellar evolution because of its composition. The measured calcium abundance
(1-10 times the solar value) in combination with the helium-rich nature of its atmosphere represents a
chemical surface composition that is not predicted by stellar evolution models.
1. How does an intermediate mass star become a white dwarf?
2. What makes this star (KPD 0005+5106) rare (2 answers)?
3. Using the H-R Diagram, what would be a likely luminosity for this star?