Question 1

The shape of the cross-section of the Roche lobes around a close binary star system, taken through the centers of both stars, is

Accepted Answer

A)  two ellipses that touch at the center of the lobes. 
B)  a sphere centered on the center of mass of the star system. 
C)  an ellipse with a star at each focus. 
D)  a figure eight.

Question 2

The spiral galaxy of which Earth is a part is roughly 14 billion years old. Which of these statements about the stars that formed when the Milky Way Galaxy was very young (say, during the first billion years) is true?

Accepted Answer

A)  No stars are still on the main sequence-in this time all stars have finished their lives. 
B)  All stars of less than 3/4 of the mass of the Sun are still on the main sequence. 
C)  All stars of more than 15 times the mass of the Sun are still on the main sequence. 
D)  All stars of 3 times the mass of the Sun are still on the main sequence.

Question 3

On a Hertzsprung-Russell diagram describing the stars in a young cluster, in which position would one expect to find the T Tauri stars?

Accepted Answer

A)  well above the main sequence and to the left 
B)  just above and slightly to the right of the main sequence 
C)  well below the main sequence 
D)  upper right, well above the main sequence

Question 4

Can astronomers observe nebulae, the regions where stars form?

Accepted Answer

A)  Yes. A number of them can be seen easily with low-power binoculars. 
B)  Yes, but a medium-size telescope (say, 16'') is required to see any of them. 
C)  Yes, but only a powerful research instrument can see them. 
D)  No. Nebulae are very short-lived phenomena. They either collapse to form star systems, or they disperse. Theoretically, it is known they exist for short periods of time, but astronomers have never observed any of them directly.

Question 5

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is

Accepted Answer

A)  very young because the G and K stars are still evolving toward the main sequence. 
B)  of indeterminate age since the age of the cluster cannot be estimated from the information given. 
C)  impossible because cool stars cannot exist above the main sequence when hot stars are on the main sequence. 
D)  old because the G and K stars are already evolving off (away from) the main sequence.

Question 6

Why do H II regions glow?

Accepted Answer

A)  The hydrogen cannot emit radiation because it is fully ionized, so the radiation comes from neighboring molecules of carbon monoxide. 
B)  The H II region collides with a giant molecular cloud exciting the molecules in the cloud to radiate. 
C)  Some H II ions unite with electrons to re-form neutral hydrogen. In this process, the electron passes from level to level in the atom and emits a cascade of photons. 
D)  The protons, which make up H II, collide with each other, resulting in gamma-ray emission from the nuclei.

Question 7

What is the characteristic color of a reflection nebula?

Accepted Answer

A)  red 
B)  yellow 
C)  green 
D)  blue

Question 8

The definition of a main-sequence star is a star

Accepted Answer

A)  with a surface temperature equal to that of the Sun. 
B)  in which nuclear fusion reactions generate sufficient energy to oppose further compression of the star. 
C)  whose age after birth is about 1 million years. 
D)  with a luminosity precisely equal to that of the Sun.

Question 9

If the universe is only 14 billion years old, which of these groups of stars have never moved beyond the main sequence?

Accepted Answer

A)  stars with masses less than 0.08 solar mass 
B)  stars with masses less than 0.75 solar mass 
C)  stars with masses greater than 100 solar masses 
D)  stars with masses greater than 10 solar masses

Question 10

Protostars are slowly

Accepted Answer

A)  expanding at the surface while the core contracts. 
B)  contracting and heating up. 
C)  heating up and expanding. 
D)  contracting and cooling.

Question 11

Which of these major perturbations can occur in a close binary system and radically alter the evolution and behavior of the two individual stars?

Accepted Answer

A)  heating of the localized areas of the atmosphere of one star by its companion 
B)  transfer of matter from one star to its companion 
C)  gravitational disturbance of one star's motion by its companion, forcing it to move in an orbit 
D)  eclipse of the light from one star by the other when viewed from Earth

Question 12

A reflection nebula is made visible by

Accepted Answer

A)  thermal energy emitted as a continuous spectrum by the very hot gas, much like that emitted by a hot body on Earth. 
B)  light from embedded stars reflected over a wide range of wavelengths toward Earth by crystals of water, methane, and ammonia ices. 
C)  emission lines from hydrogen, which itself has been ionized by UV light from embedded stars. 
D)  blue light preferentially scattered by dust grains.

Question 13

The transfer of mass from the surface of one star onto the surface of another is MOST often observed in

Accepted Answer

A)  detached binaries. 
B)  overcontact binaries. 
C)  contact binaries. 
D)  semidetached binaries.

Question 14

What is the turnoff point for a star cluster?

Accepted Answer

A)  point in the Hertzsprung-Russell diagram occupied by stars undergoing (or about to undergo) the helium flash 
B)  point in the Hertzsprung-Russell diagram occupied by the highest-mass main-sequence stars in the cluster 
C)  point in the Hertzsprung-Russell diagram occupied by the lowest-mass main-sequence stars in the cluster 
D)  point in the Hertzsprung-Russell diagram occupied by the highest-mass stars that have not yet reached the main sequence

Question 15

Which part of the Hertzsprung-Russell diagram is occupied by protostars?

Accepted Answer

A)  left of the main sequence 
B)  band running from upper right to lower left 
C)  band running from upper left to lower right 
D)  right of the main sequence

Question 16

In photographs, the Pleiades open star cluster is surrounded by a bluish haze (see Figure 13-4 in the text). What causes this blue light?

Accepted Answer

A)  starlight scattered from interstellar dust in the star cluster 
B)  starlight scattered by the light-sensitive grains in the photographic plate when the picture was taken 
C)  shock waves losing energy to interstellar gas in the star cluster, causing the atoms to emit light 
D)  starlight absorbed and reemitted by interstellar gas in the star cluster

Question 17

A relatively fast star escapes an open cluster. What does this do to the stability of the remaining cluster?

Accepted Answer

A)  The remaining cluster becomes MORE stable because only the slower stars are left. 
B)  The gravitational attraction of the escaping star tends to pull other stars after it, thus leading to the dissipation of the entire cluster. 
C)  The remaining cluster becomes LESS stable because the mass and thus the escape speed are reduced. 
D)  Because of the conservation of momentum, a second star must be expelled from the cluster in the opposite direction. The remaining cluster is then as stable as it was originally.

Question 18

The stars at the turnoff point in the Hertzsprung-Russell diagram of the Hyades star cluster have a luminosity of approximately 10 times that of the Sun, while those at the turnoff point in the cluster M41 have a luminosity of about 80 times that of the Sun. From this information, it can be said with certainty that the Hyades cluster

Accepted Answer

A)  has more stars in it than the M41 cluster. 
B)  is younger than the M41 cluster. 
C)  is farther away than the M41 cluster. 
D)  is older than the M41 cluster.

Question 19

How long ago was the Sun a ZAMS star?

Accepted Answer

A)  10 billion years 
B)  5 billion years 
C)  60 million years 
D)  187 million years

Question 20

A Roche lobe is an imaginary boundary around each star in a close binary system

Accepted Answer

A)  encompassing the mass gravitationally bound to that star. 
B)  that marks the limit outside which planets cannot form. 
C)  that marks the limit inside which planets cannot form because they would be torn apart by the star's gravity. 
D)  that marks the limit of each star's gravitational pull: As long as each star is within its own Roche lobe, the stars will have no effect on each other.

Exam 13: The Lives of Stars From Birth Through Middle Age