# ASTR 101 Chapter 12

## Unlock all answers in this set

question
The three bins represent three important properties of stars. Drag the items that we must measure in order to determine each property into the appropriate bin.
LUMINOSITY -distance -apparent brightness SURFACE TEMPERATURE -color or spectral type MASS -orbital period in binary system -orbital distance in binary system
question
To place a star on an H-R diagram, we must know its ______________.
Surface temperature and Luminosity
question
On the H-R diagram, most stars fall into the region labeled ________________.
Main Sequence
question
Among main sequence stars, those with the highest surface temperatures have _______________.
the highest masses and shortest lifetimes
question
Suppose you observe two clusters of stars: -Cluster A contains main sequence stars of nearly all masses. -Cluster B contains only low-mass main sequence stars, along with many giants. What can you conclude about their ages?
Cluster A is younger than cluster B.
question
Two stars, X and Y, have the same temperature. Star X is ten times more luminous than Star Y. Which star has the larger radius?
Star X
question
Two stars, X and Y, have the same luminosity, but star X is very blue while star Y is very red. Which star has the larger radius?
Star Y
question
Fomalhaut is an A star with a luminosity 14 times that of the Sun. Fomalhaut is therefore a
Main sequence star
question
Sirius B is a B star with a luminosity equal to 0.024 Lsun. Our Sun is a G star. Which is more massive?
Not enough information to determine
question
Use the H-R diagram to list the following three main sequence stars in order of increasing mass: The Sun, Spica, and Barnard's Star.
Barnard's Star, The Sun, Spica
question
Spica is a main sequence star, having a surface temperature of 26,000 K. In order for a star with a surface temperature of only 6000 K to have the same luminosity as Spica, its radius must be
question
The rate of fusion (the number of helium nuclei produced per second) in the core of the star Vega (a main sequence star with a temperature of about 10,000 K) is roughly
About 60 times the rate of fusion in the Sun
question
A star with the same radius as the Sun but a surface temperature five times as high would have a luminosity
About 625 times that of the Sun
question
A main sequence star with twice the mass of the Sun (and surface temperature of about 8000 K) will have a luminosity roughly
10 times as high as the Sun's luminosity
question
The figure shows a standard Hertzsprung-Russell (H-R) diagram. Label the horizontal and vertical axes using the two blanks nearest the center of each axis, and label the extremes on the two axes using the blanks on the ends of axes.
Y-Axis going up: fainter, luminosity, brighter X-Axis going from left to right: Hotter, Surface Temperature, Colder
question
Use the labels to identify what kinds of stars inhabit each region of the H-R diagram.
From bottom to top: White dwarfs, Main sequence, Red giants, Main sequence, Super giants
question
Consider the four stars shown following. Rank the stars based on their surface temperature from highest to lowest.
From highest to lowest: A blue white dwarf star, sun, an orange main sequence star, a red super giant star
question
Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s)
All of them are stacked on top of each other
question
Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part B. Ranks the stars based on their luminosity form the highest lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s).
Highest to Lowest: Highest dot to the lowest dot.
question
Five stars are shown on the following H-R diagrams. Rank the stars based on their surface temperature from highest to lowest. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).
Highest to Lowest: Dots that are furthest to the left to the dots that are furthest to the right.
question
Five stars are shown on the following H-R diagrams. Rank the stars based on their luminosity from highest to lowest; notice that these are the same five stars shown in Part D. If two (or more) stars have the same surface temperature, drag one star on top of the other(s).
All stacked on top of each other.
question
Five stars are shown on the following H-R diagrams; notice that these are the same five stars shown in Part F. Rank the stars based on their luminosity from highest to lowest. If two (or more) stars have the same luminosity, drag one star on top of the other(s)
Highest to Lowest: Two right dots stacked on top of each other, Middle dot in the middle, Two low dots stacked on top of each other.
question
Listed following is a set of statements describing individual stars or characteristics of stars. Match these to the appropriate object category.
RED GIANT OR SUPERGIANT STARS: Found in the upper right of the H-R diagram, Very cool but very luminous. MAIN SEQUENCE STARS: the sun, for example, the majority of stars in our galaxy, the hottest and most luminous stars. WHITE DWARFS: Not much larger in radius that Earth, very hot but very dim.
question
Suppose we wanted to represent all of these objects on the 1-to-10-billion scale from Chapter 1, on which the Sun is about the size of a grapefruit. Approximately how large in diameter would the star Aldebaran be on this scale?
6 meters (roughly the size of a dorm room)
question
Approximately how large in diameter would the star Betelgeuse be on this same scale?
3 kilometers (the size of a small town)
question
Approximately how large in diameter would the star Procyon B be on this same scale?
1 millimeter (the size of a grape seed)
question
What is the approximate luminosity of a star whose mass is 10 times that of the Sun?
10,000 Lsun
question
What is the approximate lifetime of a star whose mass is 10 times that of the Sun?
Slightly longer than 10^7 years
question
What is the approximate luminosity of a star whose mass is 3 times that of the Sun?
100 Lsun
question
What is the approximate lifetime of a star whose mass is 3 times that of the Sun?
Slightly shorter than 10^9 years
question
What is the approximate luminosity of a star whose mass is twice that of the Sun?
10 Lsun
question
What is the approximate lifetime of a star whose mass is twice that of the Sun?
10^9 years
question
Consider a relatively nearby, single star, that is, a star that is not a member of a binary system and has no known orbiting planets. Listed below are a few properties of this star. Classify each property as either something that we can observe or measure directly (with the aid of a telescope and instruments such as cameras or spectrographs) or something that we must infer indirectly (and hence is correct only if all of our assumptions are correct).
OBSERVE DIRECTLY: -color -parallax angle -spectral type -apparent brightness INFER INDIRECTLY: -surface temperature -luminosity -mass -radius
question
From Part A, you know that surface temperature is a stellar property that we infer indirectly. What must we measure directly so that we can infer a star's surface temperature?
Spectral type
question
Which of the following must true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light? CHECK ALL THAT APPLY.
-No interstellar gas or dust absorbs or scatters light between us and the star -We have measured the star's apparent brightness -We have measured the star's distance
question
We found that mass must be inferred for the star described in Part A. However, we can measure a star's mass directly if ___________.
it is a member of an eclipsing binary system.
question
You should now see that the reason the mass of the star in Part A must be inferred is that the star has no known orbiting objects, which means we cannot apply Newton's version of Kepler's third law. Which of the following must be true if the star's inferred mass is to be accurate? CHECK ALL THAT APPLY.
-We have determined that the star is a main sequence star -We have measured the star's spectral type
question
Before we can use parallax to measure the distance to a nearby star, we first need to know _____________.
The Earth-Sun distance
question
Which of the following is a valid way of demonstrating parallax for yourself?
Hold up your hand in front of your face, and alternately close your left and right eyes.
question
What is the cause of stellar parallax?
Earth's orbit around the Sun
question
The more distant a star, the ___________.
smaller its parallax angle.
question
Approximately what is the parallax angle of a star that is 20 light-years away?
0.16 arcsecond
question
Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years?
3.3 light-years
question
Compared to a main sequence star with a short lifetime, a main sequence star with a long lifetime is ______________.
less luminous, cooler, smaller, and less massive.
question
Compared to a high-luminosity main sequence star, stars in the upper right of the H-R diagram are _____________.
question
Compared to a low-luminosity main sequence star, stars in the lower left of the H-R diagram are __________.
question
If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would
get smaller.
question
What do we need to measure in order to determine a star's luminosity?
Apparent brightness and distance.
question
What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system?
The time between eclipses and the average distance between the stars.
question
Alpha Centauri: parallax angle of 0.7420 arcsecond. Give your answer in parsecs.
1.35 pc
question
Alpha Centauri: parallax angle of 0.7420 arcsecond. Give your answer in light-years.
4.39 light-years
question
3.50 pc
question
11.40 light-years
question
Which of these stars has the coolest surface temperature?
a K star
question
Which of these stars is the most massive?
a main sequence A star
question
Which of these stars has the longest lifetime?