Chapter 8 Flashcards
Based on measuring distances to stars, select all of the correct statements from the following list.
There are about 20,000 parsecs in an AU.
Determination of distance by observing parallax works mostly for nearby stars.
To determine the luminosity of a star, you must first know the distance.
Most stars have measurable parallax shifts.
For the distance to far stars, it is necessary to use spectroscopic parallax.
A parsec is the distance that light travels in one second.
There are no other stars within a parsec of the sun.
Determination of distance by observing parallax works mostly for nearby stars.
To determine the luminosity of a star, you must first know the distance.
For the distance to far stars, it is necessary to use spectroscopic parallax.
There are no other stars within a parsec of the sun.
Based on the intrinsic brightness of stars, select all of the correct statements from the following list.
To know how bright a star really is, you must first know its distance.
A star’s luminosity depends on its distance.
A star closer than 10 parsecs will have a brighter apparent magnitude than absolute magnitude.
Apparent magnitude is a measurement of intrinsic brightness.
The absolute magnitude of a star is the same as its apparent magnitude at a distance of 10 parsecs.
There are stars with greater and lesser magnitude than the sun.
Luminosity is determined from apparent magnitude.
To know how bright a star really is, you must first know its distance.
A star closer than 10 parsecs will have a brighter apparent magnitude than absolute magnitude.
The absolute magnitude of a star is the same as its apparent magnitude at a distance of 10 parsecs.
There are stars with greater and lesser magnitude than the sun.
Based on the diameters of stars, select all of the correct statements from the following list.
Giant and supergiant stars are always bright.
More massive stars are hotter and brighter.
The H-R diagram is a plot of sizes vs. temperatures of stars.
Both absolute and apparent magnitude are plotted on the H-R diagram.
Big stars have very sharp spectral lines.
The H-R diagram can be used to determine the distance to very distant stars.
All small stars are cool.
Giant and supergiant stars are always bright.
More massive stars are hotter and brighter.
Big stars have very sharp spectral lines.
The H-R diagram can be used to determine the distance to very distant stars.
Based on the masses of stars, select all of the correct statements from the following list.
White dwarf stars are very dense.
Most main sequence stars are of similar mass to the sun.
All stars follow the mass-luminosity relation.
Brighter main sequence stars are more massive.
Giant and supergiant stars tend to be dense.
Some stars are thinner than air.
Direct determination of mass can only be done for stars in binary systems.
White dwarf stars are very dense.
Brighter main sequence stars are more massive.
Some stars are thinner than air.
Direct determination of mass can only be done for stars in binary systems.
Based on a survey of the stars, select all of the correct statements from the following list.
White dwarfs are very rare.
Most of the sun’s neighbors are brighter than the sun.
More massive stars are rare.
Bright stars are common.
There are no giants or supergiants in the sun’s neighborhood.
Most of the sun’s neighbors are of low mass.
There are no white dwarfs in the sun’s neighborhood
More massive stars are rare.
There are no giants or supergiants in the sun’s neighborhood.
Most of the sun’s neighbors are of low mass.
If a star has a parallax of 1 second of arc, what is its distance in parsecs?
1
If a star has a parallax of 1 second of arc, what is its distance in light-years?
3,26
If a star is 10 pc away, what is its parallax in seconds of arc?
0.1
If a main-sequence star has a luminosity of 2,000 L, what is its spectral type?
spectral type B1
In the table above, which star is brightest in apparent magnitude?
star a
In the table above, which star is most luminous in absolute magnitude?
star c
In the table above, which star is largest?
star c
In the table above, which star is farthest away?
star d
Even through a telescope, a star appears to be a single star but through the spectroscope it shows a pattern of two absorption lines for each of the lines in the spectrum of a star like our sun. For each member of the pattern, one line, which is somewhat stronger than the other, is at a shorter wavelength. The weaker is at a somewhat longer wavelength. Over the 5 days the two lines merge into one then separate during the next 5 days back to the former maximum difference. However, now the stronger line is at a longer wavelength. From this evidence, there are actually ____ stars which orbit one another once every _____ days.
2;20
Even through a telescope, a star appears to be a single star but through the spectroscope it shows two absorption lines where a star like our Sun shows one. One line, which is somewhat stronger than the other, is at a shorter wavelength. Over the 5 days the two lines merge into one then separate during the next 5 days back to the former maximum difference. However, now the stronger line is at a longer wavelength. When the two lines combine in wavelength, the apparent single star dips in brightness. From this evidence, there are actually ______ stars which orbit one another in an orbit ______ to the direction from the stars to us.
2;edge-on
Determine the temperature of a star based on the following spectrum: medium-strength Balmer lines and strong helium lines.
about 18,000 K to 25,000 K
Determine the temperature of a star based on the following spectrum: weak Balmer lines and medium-strength ionized calcium lines.
about 5,000 K to 6,000 K
Determine the temperature of a star based on the following spectrum: strong Balmer lines.
about 9,000 K to 12,000 K
Determine the temperature of a star based on the following spectrum: very strong TiO bands.
about 2,000 K to 3,500 K
Use the table to find the spectral type of a star which has very weak Balmer lines and strong ionized calcium lines.
Spectral type K
Use the table to find the spectral type of a star which has medium-strength Balmer lines and strong helium lines.
Spectral type B
Use the table to find the spectral type of a star which has very weak Balmer lines and strong ionized helium lines.
Spectral type O
Use the table to find the spectral type of a star which has weak Balmer lines and medium-strength ionized calcium lines.
Spectral type G
The parallax angle of a star and the two lines of sight to the star from Earth form a long skinny triangle with a short side of which of the following?
1 AU
What is the distance to a star that has a parallax angle of 0.5 arc seconds?
2 parsecs
Why can smaller parallax angles be measured by telescopes in Earth orbit?
Earth’s atmosphere does not limit a telescope’s resolving power
At what distance must a star be to have its apparent magnitude equal to its absolute magnitude?
10 pc
The absolute magnitude of any star is equal to its apparent magnitude at a distance of 10 parsecs. Use this definition plus your knowledge of how light intensity changes with distance and how the stellar magnitude system is set up, to determine the following: If a star’s apparent visual magnitude is less than its absolute visual magnitude, which of the following is correct?
The distance to the star is less than 10 parsecs.
How can a cool star be more luminous than a hot star?
It can be more luminous if it is larger.
The sun’s spectral type is G2. What is the sun’s luminosity class?
main sequence (V)
The spectroscopic parallax method allows the distance to a star to be found without measuring its parallax angle. The “trick” is to combine a star’s easily measurable apparent brightness with its luminosity. In this H-R diagram, it is apparent that the luminosity of a spectral type A7 main-sequence star is approximately which of the following?
10 solar luminosities
A particular star with the same spectral type as the sun (G2) has a luminosity of 50 solar luminosities. What does this tell you about the star?
It must be larger than the sun.
Examine the stars Adara, Betelgeuse, Canopus, the sun, and Sirius B on this H-R diagram. A correct listing of these five stars from largest to smallest is which of the following?
Betelgeuse, Canopus, Adara, the sun, Sirius B
What are the radius and luminosity of a star that is classified as G2 III?
about 10 solar radii and 100 solar luminosities
For a particular binary star system, star B is observed to be always four times as far away from the center of mass as star A. What does this tell you about the masses of the two stars?
The ratio of star A’s mass to star B’s mass is 4 to 1.
For a particular binary star system, the ratio of the mass of star A to star B is 4 to 1. The semimajor axis of the system is 10 AU and the period of the orbits is 10 years. What are the individual masses of star A and star B?
Star A is 8 solar masses and star B is 2 solar masses.
To which luminosity class does the mass-luminosity relation apply?
main sequence
Which type of binary star is illustrated in this diagram?
spectroscopic binary
Which luminosity class has stars of the lowest density, some even less dense than air at sea level?
supergiant
The analysis of binary star orbits revealed individual masses of many pairs of stars and the discovery of the mass-luminosity relationship. In this H-R diagram, it is apparent that the mass of a spectral type A5 main-sequence star is approximately which of the following?
2.2 solar masses
In a given volume of space, the red dwarf (or lower main sequence) stars are the most abundant, however, on many H-R diagrams very few of these stars are plotted. Why?
They have very low luminosity and are difficult to detect, even when nearby.
Examine the figure shown here and consider the following absorption line spectra of four stars.
- Star W has medium strong hydrogen lines and weak ionized calcium lines.
- Star X has medium strong hydrogen lines and medium strong helium lines.
- Star Y has weak hydrogen lines and strong ionized calcium lines.
- Star Z has weak hydrogen lines and strong ionized helium lines.
List these stars in order of surface temperature from highest to lowest.
Z, X, W, Y
At what energy level are the electrons in hydrogen gas at a temperature of 25,000 K?
Most are in levels higher than energy level 2.
What does the presence of molecular bands in the spectrum of a star indicate?
The star has a low surface temperature
If a star has weak Balmer lines in its spectrum, what are possible reasons?
Either the star is much cooler than 10,000 K or the star is much warmer than 10,000 K.
Of the following sequence of spectral types, which star has the highest surface temperature?
B
Several stellar spectra are seen here. Which spectral type has the strongest (darkest) hydrogen absorption lines?
A
Examine the stellar spectra shown here. Which color of star has the strongest molecular bands (like TiO)?
red
What property of a star can broaden the width of its spectral lines?
All of these choices are correct.
How do astronomers determine the distance to nearby stars?
by observing their shifting motion against the further background stars
Why are parallax measurements from Earth limited to closer stars?
All of these choices are correct.
For what, if any, reason would an observatory on Mars be able to make more accurate parallax measurements than on Earth?
Mars has a thinner atmosphere than Earth and Mars is further from the sun than Earth, so the baseline is longer.
Would there be any advantage to measuring parallax from the moon?
Yes—the moon has no atmosphere.
Which planet would have no advantage of any kind over Earth for making parallax measurements?
Venus
Which of the planets below is doubly worse than Earth in measuring stars’ parallaxes from its surface?
Venus, since its atmosphere is much thicker than Earth’s, and would have a shorter baseline.
Which planet has only advantages and no disadvantages over Earth for making parallax measurements?
Mars
