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Astronomy exam 2 > Chapter 8(cont.) > Flashcards

Chapter 8(cont.) Flashcards

1
Q

How does an observatory in orbit help astronomers measure parallax more accurately?

A

It is above most of Earth’s atmosphere.

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2
Q

The absolute visual magnitude is an important property of a star.
What does absolute mean in this context?

A

It means that it is an indicator of an intrinsic property of a star.

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3
Q

The absolute visual magnitude is an important property of a star.
What does visual mean in this context?

A

It means that the observation is made at visible wavelengths.

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4
Q

The absolute visual magnitude is an important property of a star.
What does magnitude mean in this context?

A

A number representing the brightness of a star.

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5
Q

What is the absolute visual magnitude of a star?

A

its apparent magnitude at visible wavelengths at a distance of 10 parsecs

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6
Q

Which is true?

A

Absolute visual magnitude must be corrected before luminosity can be determined.

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7
Q

Which type of star is generally the hottest?

A

blue main sequence

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8
Q

Which type of star is generally most luminous?

A

red supergiant

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9
Q

What is necessary for a cooler star to be more luminous than a hot star?

A

It is possible if the cool star is bigger.

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10
Q

Which statement below is the most correct?

A

A cooler star can be more luminous than a hotter star if it is bigger.

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11
Q

What must be true for a star of similar mass to the sun to be larger than the sun?

A

It must be less dense than the sun.

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12
Q

Which of the stars below can be the same mass as our sun?

A

a red giant

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13
Q

What must be true for a star of similar density to the sun to be larger than the sun?

A

It must be more massive.

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14
Q

How do we know that all giant stars are larger than the sun?

A

Giants of similar mass are less dense and giants of similar density to the sun are more massive.

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15
Q

Which is true about most white dwarfs?

A

They are hotter than the sun.

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16
Q

Which is true about most white dwarfs?

A

They are dimmer than the sun.

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17
Q

We know that white dwarfs must be which of the following?

A

small, because they are hot, but dim

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18
Q

What observations would you need to classify a star according to its luminosity class?

A

the thickness of its spectral lines

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19
Q

What is one way you could determine a star’s luminosity class?

A

by its position on the H-R diagram

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20
Q

How is parallax measured in spectroscopic parallax?

A

Actually, parallax is not measured.

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21
Q

Once a star’s position on the H-R diagram is known, what is needed next to determine its distance by spectroscopic parallax?

A

apparent visual magnitude

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22
Q

Why is determining the distance to stars by spectroscopic parallax necessary?

A

Many stars are too far away to show any stellar parallax.

23
Q

A class G2 V is about ______ times as luminous as the sun

A

1

24
Q

A class G2 V is ______ times the radius of the sun.

A

1

25
Q

What observations are necessary to determine the masses of the stars in a binary system?

A

the orbital period of the system and the distance between the stars

26
Q

How do astronomers determine the masses of stars in a binary?

A

with Newton’s version of Kepler’s third law

27
Q

Which of the statements below is true for the different kinds of binary stars?

A

It is impossible to determine the inclination of a spectroscopic binary system.

28
Q

Do the stars on the main sequence illustrate the mass-luminosity relationship?

A

Yes, because more massive stars tend to burn hotter and brighter.

29
Q

Why is it difficult to find out how common the most luminous stars are?

A

because they are rare

30
Q

Why is it difficult to find out how common the least luminous stars are?

A

because most of them are so dim

31
Q

The above stars are all members of the same cluster, so what do they all have in common?

A

approximate distance from us

32
Q

What color are the brightest stars in the cluster? Some stars in the cluster have evolved off the main sequence.

A

red

33
Q

The brightest blue-white stars in the cluster are:

A

red giants

34
Q

What are the strengths of the Balmer lines in stellar spectra?

A

It depends on the temperature of the star

35
Q

Where are Balmer lines strongest?

A

in medium temperature stars

36
Q

In hot stars, which of the following is true?

A

Balmer lines are weak because electrons are often in higher orbits.

37
Q

In cool stars, which of the following is true?

A

Balmer lines are weak because electrons are often not excited.

38
Q

What is true of stellar spectra?

A

They are dark-line spectra.

39
Q

What do stellar spectra tell us about a star?

A

both temperature and composition

40
Q

What information do we get from stellar spectra?

A

It tells us mainly about the star’s photospheric surface.

41
Q

Which star on the Spectrial Classes table would have the peak strength of ionized calcium lines as shown in the figure above?

A

Arcturus

42
Q

Note the

line in the above spectra. It is strongest in which type of star?

A

A

43
Q

The peaks in line strength in the above graph correspond to the thickest dark lines in the above spectra. This shows the relationship between which of the following?

A

peak wavelength and temperature

44
Q

In which type of star in the graph above is the sodium line strongest?

A

M

45
Q

The broadest dark lines in the above spectra correspond to __________ in the graph below of intensity vs. wavelength of the spectral types.

A

the wavelength of the deepest dips

46
Q

The Doppler effect can cause spectral lines to do which of the following?

A

All of these choices are correct.

47
Q

Doppler broadening can be caused by which of the following?

A

very-fast-moving molecules in a star and rapid rotation of a star

48
Q

Which of the lists below has the stars from the above H-R diagram in order of brightness or luminosity from dimmest to brightest, left to right?

A

Barnard’s star, Sirius B, Sun, Canopus, Rigel A

49
Q

Which of the following stars from the above H-R diagram has the hottest photosphere?:

A

Rigel A

50
Q

Which of the following stars from the above H-R diagram is largest?

A

Antares

51
Q

Which of the following stars from the above H-R diagram is most massive?

A

Spica A

52
Q

Which of the type of stars below (all of about the same mass) is the most luminous (brightest)?

A

supergiant

53
Q

Stars with which of the following colors have the hottest photosphere?

A

blue

54
Q

Parallax and Distance Range. What is a good range of distances from Earth for which the stellar parallax formula is accurate? (Hints: The distances to the nearest stars is 1.30 pc. Find the resolving power for the largest optical ground telescope or find the minimum parallax uncertainty for ground-based optical telescopes and assume this corresponds to a maximum tolerable error of 10 percent.)

A

1.3-50 pc

Astronomy exam 2 (4 decks)

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