Download Stellar Evolution and the HR Diagram – Study Guide

Astronomy
Name ___________KEY___________
Stellar Evolution and the HR Diagram – Study Guide
1.
Label the five regions of the HR Diagram below on the lines provided using the words
hot and bright, hot and dim, cool and bright, cool and dim, main sequence.
HOT and Bright
COOL and Bright
*
Betelgeuse
Giants
* Rigel
Main Sequence line
* Our Sun
white dwarfs region
RedDwarfs
HOT and Dim
O
B
COOL and Dim
A
F
G
K
M
2.
On the HR Diagram above, label the spectral groups along the x-axis. OBAFGKM
3.
Spectral groups are related by color and __temperature____.
4.
Along the y-axis, there are two ways to indicate a star’s brightness, called __Absolute __
___Magnitude___ or ____Luminosity____.
5.
Luminosity means total energy output of a star.
6.
Mark with a * and label the positions of the following stars on the HR Diagram:
a. our Sun
7.
b. Betelgeuse
c. Rigel
Draw an oval and label the regions where the following types of stars can be found:
a. white dwarfs
b. red giants
c. supergiants
d. red dwarfs
7. In general, the larger surface a star has, the (more or less) luminous it is.
8. In general, the cooler a star’s surface temperature, the (more or less) luminous it is. Note
that Betelgeuse, a super RED giant is an exception—it is more luminous, but cool.
9. The majority of a star’s life is spent on the _main sequence part_____ of the graph.
10. Draw the evolutionary path of our Sun. Start by locating it’s present position on the graph
and then indicate where it will be as it ages, and finally what part of the graph it ends in.
It would start above Red Dwarfs, but below Giants; it would move down and left to the main
sequence (where it is depicted above); it would then shift up to the Giants region, and finally
down to the white dwarfs region.
11. Hottest stars are ___Blue____ in color. Coolest stars are ____Red__ in color.
12. An object whose density is so great that even light cannot escape its gravity is known as
_Black Hole____.
13. White dwarfs are about the size of __Earth (planets)__ .
14. Neutron stars are about ___12__ miles in diameter.
15. Our Sun is a G2___ class star.
16. The MOST massive of stars live (the longest or the shortest) lives.
17. Supernovas are produced by the explosion of _super massive__ stars. The remaining star is
either a _neutron star or a __black hole____.
18. All stars begin by the contraction of ______dust and gas (nebulas)____.
19. What percentage of a star’s life is spent on the main sequence? 90%
20. Stars on the main sequence are fusing _hydrogen__ into ___helium__ (name the elements).
21. Stars with the longest life spans are found _lower right (red dwarfs)_part of the HR Diagram.
22. Given an HR diagram as on your worksheet, be prepared to answer the following types of
questions:
a. What is the temperature of a G-class star? 5000-6000K
b. Which are hotter, red giants or white dwarfs?
White dwarfs (but they are dimmer)
c. Which is brighter, the sun or a white dwarf? The Sun (but not as hot)
d. Is Vega brighter than our sun? Yes (closer to upper top of diagram)
e. Is Antares hotter than our sun? No, it’s a giant, class K or M (lower on diagram)
23. Stars that move off the main sequence first move to the _Giant_ region of the HR diagram.
These stars are fusing __helium__ into ____carbon__ (name the elements).
24. What determines the eventual fate and life span of a star? Its mass at birth
25. What information does an HR Diagram give astronomers?
The HR diagram can indicate the age and life stage of a star, the type of star it is (super giant,
white dwarf, main sequence), as well as how bright and how hot a star is.
26. What information can a star’s spectrum give astronomers?
Spectra give information about chemical composition, temperature and the motion of a star.
27. Given a star pattern of Orion, locate and label
Betelgeuse (upper left) = RED GIANT
Betelguese, Rigel, and the star-forming nebula.
Rigel (lower right) = MAIN SEQUENCE
Which is a red giant? …a main sequence star
Orion nebular is under belt stars
28. MINI-Essay: Explain Carl Sagan’s quote: We are star stuff.
All the elements in the universe were made by fusion of lighter elements in the stars. When a
MASSIVE star goes supernova, all the heavy elements are made, elements such as
phosphorus, magnesium, iron, and calcium that make up our bodies. So we really are made
of atoms that were formed first in the dying explosions of long dead stars.
29. MINI-Essay: How is a supernova both a beginning and an end?
Supernovae are the result of the death of a star that can no longer carry out fusion. All the
elements that made of the star (and new ones made in the supernova explosion) are ejected as
gas clouds into space where they can re-form star-building nebulas. In addition, the
supernova shock wave can cause interstellar gas to start collapsing and heat up, thus starting
the beginning of new stars.
30. The life sequence, beginning with dust and gas, of an O (super massive), A (medium mass,
<5 sun mass), and a G class star.
O Star: nebula  blue star  Super red giant  Super nova  Black Hole
A Star: nebula  whitestar  Super red giant  Super nova  Neutron Star
G Star: nebula  yellow star  Red giant  Planetary Nebula  White Dwarf
Possible Bonus Questions:
1. Where on an HR diagram are you most likely to find our closest stars?
(Main Sequence, lower right)
2. What is Mrs. Soltis’ favorite star? (Aldebaran)