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CHAPTER 9—THE FAMILY OF STARS

MULTIPLE CHOICE

	1.	The hydrogen lines in spectral type A stars
a. | are most narrow for supergiants.
b. | are most narrow for main sequence stars.
c. | can not be used to estimate the luminosity of the star.
d. | are very weak and difficult to see.
e. | are useful in determining the apparent magnitude of the star.

ANS:	A	PTS:	1

	2.	Parallax would be easier to measure if
a. | Earth's orbit was larger.
b. | the stars were farther away.
c. | Earth moved faster along its orbit.
d. | all of these
e. | none of these

ANS:	A	PTS:	1

	3.	Absolute visual magnitude is
a. | the apparent magnitude of a star observed from Earth.
b. | the luminosity of a star observed from a distance of 1000 pc.
c. | the apparent magnitude of a star observed from a distance of 10 pc.
d. | the luminosity of a star observed from Earth.
e. | c and d

ANS:	C	PTS:	1

	4.	A star's luminosity depends only on the star's
a. | distance and diameter.
b. | temperature and distance.
c. | distance.
d. | temperature and diameter.
e. | apparent magnitude.

ANS:	D	PTS:	1

	5.	In an H-R Diagram, stars with the smallest radius are found in the ____ of the diagram.
a. | center
b. | upper left corner
c. | upper right corner
d. | lower left corner
e. | lower right corner

ANS:	D	PTS:	1

	6.	In the H-R diagram, 90 percent of all stars are
a. | in the giant region.
b. | in the supergiant region.
c. | among the B stars.
d. | among the G stars.
e. | on the main sequence.

ANS:	E	PTS:	1

	7.	We know that giant stars are larger in diameter than the sun because
a. | they are more luminous but have about the same temperature.
b. | they are less luminous but have about the same temperature.
c. | they are hotter but have about the same luminosity.
d. | they are cooler but have about the same luminosity.
e. | they have a larger absolute magnitude than the sun.

ANS:	A	PTS:	1

	8.	Red giant stars are

I. | more luminous than the sun.
II. | larger in diameter than the sun.
III. | cooler than B stars.
IV. | located above the main sequence stars in the H-R diagram.

a. | I & II
b. | II & IV
c. | I, II, & IV
d. | II, III, & IV
e. | I, II, III, & IV

ANS:	E	PTS:	1

	9.	Compared with the spectral lines in the solar spectrum, lines in a supergiant star’s spectrum are
a. | more narrow.
b. | broader.
c. | weaker.
d. | stronger.
e. | b & c

ANS:	A	PTS:	1

	10.	The most common stars are
a. | supergiants.
b. | giants.
c. | upper (more luminous) main sequence stars.
d. | white dwarfs.
e. | lower (less luminous) main sequence stars.

ANS:	E	PTS:	1

	11.	The ____ of a star is a measure of the total energy radiated by the star in one second.
a. | color
b. | apparent visual magnitude
c. | luminosity class
d. | spectral type
e. | luminosity

ANS:	E	PTS:	1

	12.	The star named Sheat is of M2 II spectral type and luminosity class. Based on this information, which of the following are true?

I. | Sheat has a surface temperature less than the sun.
II. | Sheat has a diameter that is greater than that of the sun.
III. | Sheat is more luminous than the sun.
IV. | Sheat is located near the upper left hand corner in the HR diagram.

a. | I & II
b. | II & IV
c. | II, III, & IV
d. | I, II, & III
e. | I, II, III, & IV

ANS:	D	PTS:	1

	13.	The star named Circini has the spectral type and luminosity class of  O 8.5 V. Based on this information, which of the following are true?

I. | Circini has a surface temperature less than the sun.
II. | Circini has a diameter that is greater than that of the sun.
III. | Circini is more luminous than the sun.
IV. | Circini is located near the upper left hand corner in the HR diagram.

a. | I & II
b. | II & IV
c. | II, III, & IV
d. | I, II, & III
e. | I, II, III, & IV

ANS:	C	PTS:	1

	14.	To determine the orbital period of a visual binary, we must measure
a. | brightness.
b. | position on the sky.
c. | wavelengths.
d. | luminosity.
e. | temperature.

ANS:	B	PTS:	1

	15.	In a binary system, the more massive star
a. | is at the center of mass.
b. | is farthest from the center of mass.
c. | is nearest the center of mass.
d. | follows the largest orbit.
e. | shows a larger Doppler shift in its spectral lines.

ANS:	C	PTS:	1

	16.	Spectroscopic binaries are difficult to analyze because
a. | we can't measure the radial velocities of each star in the system.
b. | we can't see the shape or tilt of the orbit.
c. | we can't find the diameters of the stars.
d. | we can't determine the luminosities of the stars.
e. | the Doppler shift is not measurable.

ANS:	B	PTS:	1

Use the HR diagram below to answer the following question(s).

	17.	Which star in the diagram is most like the sun?
a. | Alnilam
b. | Antares
c. | Arcturus
d. | HR 5337
e. | Sirius B

ANS:	D	PTS:	1

	18.	Which star in the diagram has the greatest surface temperature?
a. | Alnilam
b. | Antares
c. | Arcturus
d. | HR 5337
e. | Sirius B

ANS:	A	PTS:	1

	19.	Which of the stars in the diagram has the largest absolute visual magnitude?
a. | Alnilam
b. | Antares
c. | Arcturus
d. | HR 5337
e. | Sirius B

ANS:	E	PTS:	1

	20.	An eclipsing binary will
a. | be more luminous than a visual binary.
b. | also be observed as a spectroscopic binary.
c. | give off most of its light in the infrared.
d. | show a constant Doppler shift in its spectral lines.
e. | show two stars with variable proper motion.

ANS:	B	PTS:	1

	21.	If we can solve the orbital motion of an eclipsing binary, we can find
a. | the mass of each star.
b. | the diameter of each star.
c. | the distance to the binary.
d. | all of the above
e. | both a and b

ANS:	E	PTS:	1

	22.	Which of the following kinds of stars best obey the mass-luminosity relation?
a. | main sequence stars
b. | giant stars
c. | supergiant stars
d. | white dwarfs
e. | all of the above

ANS:	A	PTS:	1

	23.	Which of the following kinds of stars is most dense?
a. | a supergiant star
b. | a main sequence star
c. | a giant star
d. | a white dwarf
e. | the sun

ANS:	D	PTS:	1

	24.	A spectroscopic binary shows periodic variations in its
a. | radial velocity.
b. | proper motion.
c. | brightness.
d. | mass.
e. | spectral type.

ANS:	A	PTS:	1

	25.	Stars on the main sequence with the greatest mass
a. | are spectral type M stars.
b. | are spectral type O stars.
c. | are located at the bottom of the main sequence in the HR diagram.
d. | have masses very similar to the sun.
e. | both b and c

ANS:	B	PTS:	1

	26.	The star Algol is
a. | an astrometric binary.
b. | a spectroscopic binary.
c. | a visual binary.
d. | an eclipsing binary.
e. | both b and d

ANS:	E	PTS:	1

	27.	The total mass of a binary system can be calculated from
a. | the ratio of the angular separation from the center of mass of each of the stars.
b. | the distance to the binary and its radial velocity.
c. | the semi major axis and period of the orbit.
d. | the radial velocities of the two stars.
e. | the time required for the small star to eclipse the larger star.

ANS:	C	PTS:	1

	28.	The diagram below illustrates two stars in a visual binary system and the center of mass of this system. Based on this diagram, what is the ratio of the mass of star A to the mass of star B?

a. | 2 to 1
b. | 1 to 2
c. | 2 to 3
d. | 3 to 2
e. | 1 to 3

ANS:	B	PTS:	1

	29.	If a star has a parallax of 0.02 seconds of arc, then its distance is
a. | 20 pc
b. | 50 pc
c. | 2 pc
d. | 5 pc
e. | 500 pc

ANS:	B	PTS:	1

	30.	If a star with an absolute magnitude of −5 has an apparent magnitude of +5, then its distance is
a. | 1 pc.
b. | 10 pc.
c. | 100 pc.
d. | 1000 pc.
e. | 10,000 pc.

ANS:	D	PTS:	1

	31.	An eclipsing binary has been analyzed and it has been determined that the ratio of the mass of star A to the mass of star B is 6 and the total mass of the two stars is 26 solar masses. What are the masses of star A and star B?
a. | Star A has a mass of 1 solar mass and star B has a mass of 6 solar masses.
b. | Star A has a mass of 20 solar mass and star B has a mass of 6 solar masses.
c. | Star A has a mass of 31.2 solar mass and star B has a mass of 5.2 solar masses.
d. | Star A has a mass of 22.3 solar mass and star B has a mass of 3.7 solar masses.
e. | The masses of star A and star B cannot be determined from the information given.

ANS:	D	PTS:	1

	32.	What is the total mass of a binary star system with P = 20 yr and a = 10 AU?
a. | 2 solar masses
b. | 2.5 solar masses
c. | 0.5 solar mass
d. | 80 solar masses
e. | 0.4 solar mass

ANS:	B	PTS:	1

	33.	The diagram below shows the radial velocity curve of a double-line spectroscopic binary. Based on this radial velocity curve, which of the following statements is correct?

a. | Star A is twice the mass of star B.
b. | Star B is twice the mass of star A.
c. | Star A is ten times the mass of star B.
d. | Star B is ten times the mass of star A.
e. | Star A and Star B have the same mass.

ANS:	B	PTS:	1

	34.	In the light curve below, what is the period of the eclipsing binary?

a. | 5 days
b. | 32.5 days
c. | 7.5 days
d. | 42.5 days
e. | 50 days

ANS:	B	PTS:	1

	35.	At what point in the light curve below is the cooler star in front of the hotter star?

a. | 1
b. | 2
c. | 3
d. | 4
e. | 5

ANS:	D	PTS:	1

Use the chart below to answer the following question(s).

Star

m_v

M_v

d (pc)

Parallax
(sec of arc)

Spectral
Type

65 Tau | 4.2 | | | 0.025 | A7 IV
HR 4621 | 2.6 | −0.3 | | | B2 IV
α Pic | | 1.8 | 20 | | A7 V
58 Ori | | −6.0 | | 0.005 | M2 I
HR 2491 | −1.5 | | 2.5 | | A1 V

	36.	From the data given, which star in the table would appear the faintest in the night sky?
a. | 65 Tau
b. | HR 4621
c. | α Pic
d. | 58 Ori
e. | HR 2491

ANS:	A	PTS:	1

	37.	From the data given,, which star in the table has the greatest luminosity?
a. | 65 Tau
b. | HR 4621
c. | α Pic
d. | 58 Ori
e. | HR 2491

ANS:	D	PTS:	1

	38.	From the data given,, which star in the table is the closest to Earth?
a. | 65 Tau
b. | HR 4621
c. | α Pic
d. | 58 Ori
e. | HR 2491

ANS:	E	PTS:	1

	39.	From the data given,, which star in the table has the greatest surface temperature?
a. | 65 Tau
b. | HR 4621
c. | α Pic
d. | 58 Ori
e. | HR 2491

ANS:	B	PTS:	1

	40.	From the data given,, which star in the table has the greatest diameter?
a. | 65 Tau
b. | HR 4621
c. | α Pic
d. | 58 Ori
e. | HR 2491

ANS:	D	PTS:	1

Use the chart below to answer the following question(s).

Star

d (pc)

Parallax 
(sec of arc)

Spectral
Type

δ Cen | | 0.026 | B2 IV
HR 4607 | | 0.039 | G8 III
HR 4758 | 20 | | G0 V
HD 39801 | | 0.005 | M2 I
9 CMa | 2.5 | | A1 V

	41.	Which star in the table is the closest to Earth?
a. | δ Cen
b. | HR 4607
c. | HR 4758
d. | HD 39801
e. | 9 CMa

ANS:	E	PTS:	1

	42.	Which star in the table has the greatest surface temperature?
a. | δ Cen
b. | HR 4607
c. | HR 4758
d. | HD 39801
e. | 9 CMa

ANS:	A	PTS:	1

	43.	Which star in the table has the greatest diameter?
a. | δ Cen
b. | HR 4607
c. | HR 4758
d. | HD 39801
e. | 9 CMa

ANS:	D	PTS:	1

	44.	If the orbital velocity of an eclipsing binary is 97 km/sec and the smaller star is completely eclipsed in 2 hours, what is the diameter of the smaller star?
a. | 175,000 km
b. | 350,000 km
c. | 194 km
d. | 700,000 km
e. | 4656 km

ANS:	D	PTS:	1

	45.	From the mass-luminosity relation, a 2 solar mass star on the main sequence would have a luminosity of approximately ____ solar luminosities.
a. | 2
b. | 4
c. | 11
d. | 0.5
e. | 0.25

ANS:	C	PTS:	1

	46.	If two stars are emitting the same amount of light, the star that is farther will appear
a. | brighter.
b. | dimmer.
c. | redder.
d. | bluer.
e. | They will have the same brightness as seen from Earth.

ANS:	B	PTS:	1

	47.	We can determine the surface temperature of a star from
a. | studying its continuous spectrum.
b. | studying its line absorption spectrum.
c. | measuring the star's luminosity.
d. | Both a and c
e. | All of a, b, and c

ANS:	E	PTS:	1

	48.	Which stars always have large positive absolute magnitude?
a. | Stars of high luminosity.
b. | Stars of low luminosity.
c. | Nearby stars.
d. | Distant stars.
e. | Not enough information given.

ANS:	B	PTS:	1

	49.	How do humans use their eyes to measure relative distance by parallax?
a. | By continuously focusing our eyes on distant objects we can determine distance.
b. | Since our eyes are separated the brain interprets the relative look angles of these eyes in terms of distance to the object viewed.
c. | Our eyes can measure the time it takes light to travel from an object and from this we get distance.
d. | By moving our heads from side to side our brain compares look angles from each of these positions to obtain the distance to the object viewed.

ANS:	B	PTS:	1

	50.	How can we tell that some stars are relatively close to us in the sky?
a. | Some stars are occasionally eclipsed by the Moon, so they must be nearby.
b. | Some stars vary in brightness caused by sunspots we can see because they are so close.
c. | Some stars appear to be extremely bright and must therefore be very close to us.
d. | Some stars appear to move periodically back and forth against the background stars because of the Earth's movement around the Sun.

ANS:	D	PTS:	1

	51.	The most accurate way to determine the surface temperature of a star is to study
a. | the pattern of absorption lines from various atoms.
b. | the relative intensities of light measured through different photometric filters.
c. | the peak wavelength of the star's continuum blackbody spectrum.
d. | pattern of emission lines that are on the star's spectrum.

ANS:	A	PTS:	1

	52.	If you compare two stars,
a. | the one with the larger radius will always have the greater luminosity.
b. | the one with the higher surface temperature will always have the greater luminosity.
c. | the one with the smaller absolute magnitude will always have the greater luminosity.
d. | the one with the larger surface area has the greater energy flux from its surface.

ANS:	C	PTS:	1

	53.	Stars in the upper right part of the Hertzsprung-Russell diagram are always ____ when compared to stars near the middle of the diagram.
a. | cooler
b. | brighter as seen from Earth
c. | larger
d. | smaller
e. | more massive

ANS:	C	PTS:	1

	54.	How is a luminosity class assigned to a star?
a. | By combining the apparent magnitude with the star's parallax.
b. | By measuring the period of variability in the star's apparent magnitude.
c. | By studying the absorption line width in the spectrum of the star.
d. | By observing the angular size of the star's image in a photograph or digital image.

ANS:	C	PTS:	1

	55.	The two most abundant elements in the sun are
a. | nitrogen and oxygen.
b. | hydrogen and helium.
c. | sulfur and iron.
d. | carbon and hydrogen.
e. | carbon and nitrogen.

ANS:	B	PTS:	1

COMPLETION

	1.	The parallax of the star 75 Leo is 0.10 and its apparent visual magnitude is +5.18. The absolute visual magnitude of 75 Leo is ____________________.

ANS:	+5.18

PTS:	1

	2.	A G2 I star is ____________________ in diameter and ____________________ luminous than the sun.

ANS:	Larger; more

PTS:	1

	3.	____________________ can be used to determine the distance to a star when the spectrum of the star can be used to determine its spectral type and luminosity class.

ANS:	Spectroscopic parallax

PTS:	1

	4.	Luminosity class IV objects are known as ____________________.

ANS:	subgiants

PTS:	1

	5.	On the HR diagram below, indicate the location of the white dwarf stars.

ANS:	An elongated region should be indicated that stretches from a luminosity of about 10^-2 and spectral type B to luminosity of about 10^-4 and spectral type G. (See Figure 12-12 in the text.)

PTS:	1

	6.	For stars on the main sequence, the luminosity can be estimated by the formula L = ____________________.

ANS:	M^3.5

PTS:	1

	7.	The masses and diameters of each star in the binary can be determined from ____________________ binaries.

ANS:	eclipsing

PTS:	1

	8.	Below is a radial velocity curve for a spectroscopic binary. Which of the stars is most massive? ____________________

ANS:	Star B

PTS:	1

	9.	If we divide the mass of a star by its volume we calculate the star's ____________________.

ANS:	average density

PTS:	1

	10.	Most stars on the H-R diagram are on the ____________________.

ANS:	main-sequence

PTS:	1

	11.	The largest of the red stars are the ____________________ stars.

ANS:	supergiant

PTS:	1

TRUE/FALSE

	1.	A star whose parallax is 0.01 seconds arc is at a distance of 1000 pc.

ANS:	F	PTS:	1

	2.	The absolute magnitude of a star is the apparent magnitude it would have if it were 10 pc from Earth.

ANS:	T	PTS:	1

	3.	The location of a star in the HR diagram indicates its temperature and intrinsic brightness.

ANS:	T	PTS:	1

	4.	Absorption lines in the spectra of supergiant stars are broader than the same spectral lines in main sequence stars of the same spectral type.

ANS:	F	PTS:	1

	5.	Giant stars are members of luminosity class III.

ANS:	T	PTS:	1

	6.	If a star is twice as hot as the sun and only half the sun's diameter, it will be less luminous than the sun.

ANS:	F	PTS:	1

	7.	The method of spectroscopic parallax cannot be applied to stars beyond about 100 pc.

ANS:	F	PTS:	1

	8.	The most common kinds of stars are low-luminosity stars.

ANS:	T	PTS:	1

	9.	Supergiants are about as common as the sun.

ANS:	F	PTS:	1

	10.	White dwarfs have such a low luminosity that even the nearest white dwarfs are not visible to the naked eye.

ANS:	T	PTS:	1

	11.	To observe a visual binary, we must measure radial velocities.

ANS:	F	PTS:	1

	12.	The more massive star in a binary system is always farthest from the center of mass.

ANS:	F	PTS:	1

	13.	If a binary system has a period of 4 years and a separation of 5 AU, then the total mass is 7.8 solar masses.

ANS:	T	PTS:	1

	14.	To observe a spectroscopic binary, we must be able to see both stars individually.

ANS:	F	PTS:	1

	15.	We can find the masses and diameters of stars that are in eclipsing binary systems.

ANS:	T	PTS:	1

	16.	When we see a binary system producing eclipses, we know that the orbit is nearly edge-on.

ANS:	T	PTS:	1

	17.	The most massive main-sequence stars are the M stars.

ANS:	F	PTS:	1

	18.	The densest stars in the H-R diagram are the white dwarfs.

ANS:	T	PTS:	1

	19.	An M star is hotter than an O star.

ANS:	F	PTS:	1

	20.	On the H-R diagram, lines of constant radius slants down from left to right.

ANS:	T	PTS:	1

	21.	The luminosity of a star is the total amount of energy it radiates each second.

ANS:	T	PTS:	1

ESSAY

	1.	Why would parallaxes be easier to observe if Earth were farther from the sun?

ANS:	
Answer not provided.

PTS:	1

	2.	How does absolute visual magnitude tell us the intrinsic brightness of a star?

ANS:	
Answer not provided.

PTS:	1

	3.	How do absolute visual magnitude and luminosity differ?

ANS:	
Answer not provided.

PTS:	1

	4.	How does an H-R diagram make it clear that giant stars are larger than main-sequence stars of the same temperature?

ANS:	
Answer not provided.

PTS:	1

	5.	How does the luminosity depend on temperature for stars of the same size?

ANS:	
Answer not provided.

PTS:	1

	6.	How can we be certain that white dwarfs are very small?

ANS:	
Answer not provided.

PTS:	1

	7.	How do the spectra of giants, supergiants, and main-sequence stars differ?

ANS:	
Answer not provided.

PTS:	1

	8.	How can we find the distance to a star that is too distant to have a measurable parallax?

ANS:	
Answer not provided.

PTS:	1

	9.	What is the most common kind of star? What measurements must be made to discover this information?

ANS:	
Answer not provided.

PTS:	1

	10.	Why is it difficult to decide how common hot stars are?

ANS:	
Answer not provided.

PTS:	1

	11.	Describe the measurements needed to determine the orbit of a visual binary star.

ANS:	
Answer not provided.

PTS:	1

	12.	What measurements are needed to determine the orbital motion of a spectroscopic binary star?

ANS:	
Answer not provided.

PTS:	1

	13.	What information can we get from eclipsing binaries that we cannot get from visual binaries?

ANS:	
Answer not provided.

PTS:	1

	14.	What information about orbital inclination can we get from visual binaries, spectroscopic binaries, and eclipsing binaries?

ANS:	
Answer not provided.

PTS:	1

	15.	For what kinds of stars are the masses of stars in the H-R diagram “orderly”? For what kinds of stars are they disorderly?  In other words, could you guess the mass of a star from its location (luminosity, temperature) on the HR diagram?

ANS:	
Answer not provided.

PTS:	1

	16.	How does density divide the stars in the H-R diagram into three groups?

ANS:	
Answer not provided.

PTS:	1

	17.	Which are the most common stars, massive stars or low-mass stars (relative to the sun)? High luminosity or low luminosity (relative to the sun)?

ANS:	
Answer not provided.

PTS:	1

	18.	Why is spectroscopy of binary stars such an important aspect of astronomy?

ANS:	
Answer not provided.

PTS:	1