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9-11 flashcards > Chapter 7/8 > Flashcards

Chapter 7/8 Flashcards

1
Q

A star’s absolute brightness is calculated at a standard distance of 10 parsecs

A

true

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2
Q

All stars produce an absorption spectra

A

true

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3
Q

Recently discovered brown dwarfs have spectra similar to cool O-type stars.

A

true

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4
Q

The spectral classification of stars started with the amount of hydrogen present in their spectra, but a
better method now uses the amount of oxygen in the star’s spectra

A

false

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5
Q

The Hertzsprung-Russell Diagram is a plot for stars using absolute magnitude versus temperature

A

true`

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6
Q

If two stars are emitting the same amount of light, the star that is farther will appear dimmer

A

true

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7
Q

Stars of low luminosity will always have large positive absolute magnitude

A

true

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8
Q

The most accurate way to determine the surface temperature of a star is to study the pattern of emis-
sion lines from various atoms.

A

true

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9
Q

A star’s apparent magnitude is a measure of how bright it appears to us if it is at its actual distance

A

true`

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10
Q

The luminosity class is assigned to a star by studying the absorption lines in the spectrum of the star

A

true

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11
Q

Our Sun’s spectral temperature type is classified as a(n) ____ on the spectral sequence

A

G star

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12
Q

hich star has the highest density (mass per unit volume

A

white dwarf

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13
Q

Which star has the largest diameter?

A

super giant

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14
Q

In which spectral sequence are the hottest stars categorized?

A

0 stars

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15
Q

he formula mV − M V can be used to calculate a star’s _____

A

distance

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16
Q

Recent discoveries of two types of brown dwarfs have placed these stars near which spectral type of
star?

A

cooler than M stars

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17
Q

The classification of stellar spectra started with the amount of hydrogen in the star’s spectrum; howev-
er, now a better scheme uses the star’s _____

A

temperature

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18
Q

The Hertzsprung-Russell diagram can be labeled many different ways. Which coordinates CANNOT be
used on an H-R diagram?

A

radius VS temperature

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19
Q

Careful measurements reveal that a star maintains a steady apparent brightness at most times, except
that at precise intervals of 93 hours. the star becomes dimmer for about 2 hours. The most likely ex-
planation for this is that the star

A

member of an eclipsing star

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20
Q

How do astronomers determine the distance to stars that are farther than 100 parsecs away

A

spectroscopic parallax

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21
Q

How did astronomers discover the relationship between spectral type and mass for main sequence
stars?

A

by measuring the masses

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22
Q

Remember Kepler’s third law, which relates the period of revolution to the average distance to a
planet. How do we modify that law to use with binary stars

A

add the mass of total two stars

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23
Q

The luminosity of a star is the

A

total energy in one second

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24
Q

The Balmer series of hydrogen absorption lines in stars is located in what part of the electromagnetic
spectrum?

A

visible region

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25
Q

The Sun is what spectral type

A

G type

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26
Q

Any star that is more luminous than the Sun, but has the same temperature as the Sun, is a(n)

A

giant

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27
Q

A supergiant star’s radii may extend out to the

A

orbit of saturn

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28
Q

Vega is an A0 main sequence star. Based on this information, which statement is true

A

vega has a mass thats greater than the sun

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29
Q

Groombridge 34 is an M2 main sequence star. Based on this information, which statement is true

A

less luminous than the sun

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30
Q

The hydrogen lines of spectral type A main sequence stars are

A

the most narrow

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31
Q

On the H-R diagram, lines of constant radius are illustrated as

A

slopping downward from left to right

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31
Q

On the H-R diagram, lines of constant radius are illustrated as

A

slopping downward from left to right

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32
Q

Hydrogen lines are weak in the spectra of hot O-type stars because

A

most hydrogen is ionized

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33
Q

Absolute visual magnitude is calculated at a standard distance of

A

10 parcecs

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34
Q

The stellar parallax limit for ground-based telescopes is accurate for stars closer than

A

100 parcescs

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35
Q

A star’s absolute visual magnitude depends only on the star’s ______ and _____

A

distance and magnitude

36
Q

On the H-R diagram, 80 percent of all stars are

A

main sequence stars

37
Q

the common type of stars

A

red dwarf stars

38
Q

last common type of stars

A

upper main sequence

39
Q

One of the factors that a large molecular cloud must overcome in order for gravitational
contraction to begin is the rotation energy of the gas.

A

true

40
Q

One of the factors that a large molecular cloud must overcome in order for gravitational
contraction to begin is the thermal energy of the gas.

A

true

41
Q

The proton-proton chain for fusing hydrogen into helium is a much more complicated process
than the CNO Cycle for fusing hydrogen into helium.

A

false

42
Q

The temperature at the core of a star must be at least 1 million degrees Kelvin before fusion
can begi

A

false

43
Q

Main sequence O stars have convective cores because they fuse hydrogen in the proton-proton
chain.

A

false

44
Q

Main sequence O stars have convective cores because they fuse hydrogen in the proton-proton
chain.

A

false

45
Q

Low mass stars like the Sun transport energy near their surface using convection

A

true

46
Q

Four of following are factors that must be overcome by a large molecular cloud before gravitational contraction can begin. Which one is the exception

A

intense radation by a nearby star

47
Q

Which trigger could start the gravitational contraction of a molecular cloud?

A

collision of mollecular clouds

48
Q

When a large gas cloud starts to collapse in a free-fall due to gravity, the cloud will _

A

increase in temperature

49
Q

After a protostar has progressed in its development, it will have a dense inner part and an outer
envelope called a(n)

A

cocoon

50
Q

Where is the Trapezium found?

A

orion nebula

51
Q

As the protostar contracts gravitationally, it will rotate faster and faster and produce a(n)

A

protostellar disk

52
Q

Stellar winds and _____ will eventually blow away the protostellar disk and remnant cocoons
of a protostar apart

A

radiation pressure

53
Q

The Sun, a one solar mass star, will take approximately how many years to go from protostar
to main sequence star?

A

30 million years

54
Q

A protostar will continue to collapse due to gravity until it reaches the main sequence, and then
gravitational collapse will stop when _____ begins

A

fusion of hydrogen

55
Q

How do large mass stars in the upper region of the main sequence produce energy

A

fusing hydrogen by CNO

56
Q

How do low mass stars in the lower region of the main sequence produce their energy

A

fusing hydrogen through PP chain

57
Q

. During the main sequence lifetime of a star of any mass, the core of the star will be composed
mainly of

A

hydrogen

58
Q

What is the resistance of a gas to the flow of radiation

A

opacity

59
Q

Pre-main sequence stars (not protostars) on the H-R Diagram are

A

above and to the right

60
Q

H II Regions are also called emission nebulae

A

true

61
Q

. Nebula is just another name for the interstellar medium (ISM

A

true

62
Q

Stars are born in reflection nebulae.

A

false

63
Q

The intercloud medium is believed to make up 90 percent of the mass of the interstellar medium.

A

false

64
Q

Elements such as carbon, silicon and oxygen have been produced in stars and expelled as stars age in
the interstellar medium. This is most likely due to these elements having cooled and condensed from
aging stars to form dust grains, and carried out by a powerful winds.

A

true

65
Q

The composition of the interstellar dust suggests that it is formed primarily in the atmospheres of cool
stars

A

true

66
Q

Because blue light has a shorter wavelength than red light, it will be more readily scattered

A

true

67
Q

X-rays come from certain regions of the interstellar medium because gas molecules in those regions
are at a very high density

A

false

68
Q

The coronal gas in the interstellar medium has very high temperatures similar to the Sun’s corona.

A

true

69
Q

. Calculations of the Sun’s future evolution indicate that it will blow away almost half of its mass in
several relatively short episodes about 4 to 5 billion years from now before it is finally extinguished.

A

false

70
Q

Stars are born from the interstellar medium, and aging or dying stars return gas and dust back into the
interstellar medium

A

true

71
Q

Interstellar extinction and the reddening of light by the interstellar medium (ISM) are both caused by

A

only dust in the ism

72
Q

he interstellar medium is composed of mainly

A

mostly gas and some diet

73
Q

Observing at a wide range of wavelengths, astronomers have detected more than ______ different
molecules in the ISM

A

150

74
Q

The ground state of hydrogen has two closely-spaced energy levels, where one electron is spinning up
and the other is spinning down. This energy transition corresponds to releasing excess energy as a photon at
what wavelength?

A

21cm

75
Q

H I clouds can be observed using

A

21 CM radiation

76
Q

The emission lines from O III are called ____ because they are not visible laboratories on Earth due
to the much greater pressure of the gas on Earth

A

forbiddeenn!!!

77
Q

. Molecular clouds are mapped using _____ gas instead of the most-abundant hydrogen because it
radiates at radio wavelengths more efficiently.

A

carbon monoxide

78
Q

The pressure of a gas depends on the ____ and ____ of the gas.

A

temp and volume

79
Q

What is the most abundant element in the interstellar medium?

A

hydrogen

80
Q
  1. Molecules in the interstellar medium emit radiation at what wavelengths?
A

radio

81
Q

Large molecular clouds will form into protostars because of

A

gravitational contraction

82
Q

Coronal gas emits x-rays and has temperatures of

A

106K

83
Q

Which mission is mapping the heliosphere’s boundary

A

interstellar boundry

84
Q

Which telescope imaged the center of the Milky Way Galaxy at a wavelength of 8 microns to
reveal the distribution of the dusty interstellar medium?

A

splitzer space

85
Q

Which type of nebulae is produced when short-wavelength scatters from the dust and displays a
blue hue?
a

A

reflection nebula

86
Q

Which type of nebulae are twisted and distorted clouds of gas and dust dense enough to obstruct
the view of the more distant stars?

A

dark nebulae

87
Q

Which type of nebula is produced when a star, hotter than 25,000 K, excites the gas near it to
produce an emission spectrum producing a distinctive pink color

A

emmision nebula

9-11 flashcards (1 decks)

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