Chapter 8(cont.) Flashcards
How does an observatory in orbit help astronomers measure parallax more accurately?
It is above most of Earth’s atmosphere.
The absolute visual magnitude is an important property of a star.
What does absolute mean in this context?
It means that it is an indicator of an intrinsic property of a star.
The absolute visual magnitude is an important property of a star.
What does visual mean in this context?
It means that the observation is made at visible wavelengths.
The absolute visual magnitude is an important property of a star.
What does magnitude mean in this context?
A number representing the brightness of a star.
What is the absolute visual magnitude of a star?
its apparent magnitude at visible wavelengths at a distance of 10 parsecs
Which is true?
Absolute visual magnitude must be corrected before luminosity can be determined.
Which type of star is generally the hottest?
blue main sequence
Which type of star is generally most luminous?
red supergiant
What is necessary for a cooler star to be more luminous than a hot star?
It is possible if the cool star is bigger.
Which statement below is the most correct?
A cooler star can be more luminous than a hotter star if it is bigger.
What must be true for a star of similar mass to the sun to be larger than the sun?
It must be less dense than the sun.
Which of the stars below can be the same mass as our sun?
a red giant
What must be true for a star of similar density to the sun to be larger than the sun?
It must be more massive.
How do we know that all giant stars are larger than the sun?
Giants of similar mass are less dense and giants of similar density to the sun are more massive.
Which is true about most white dwarfs?
They are hotter than the sun.
Which is true about most white dwarfs?
They are dimmer than the sun.
We know that white dwarfs must be which of the following?
small, because they are hot, but dim
What observations would you need to classify a star according to its luminosity class?
the thickness of its spectral lines
What is one way you could determine a star’s luminosity class?
by its position on the H-R diagram
How is parallax measured in spectroscopic parallax?
Actually, parallax is not measured.
Once a star’s position on the H-R diagram is known, what is needed next to determine its distance by spectroscopic parallax?
apparent visual magnitude
Why is determining the distance to stars by spectroscopic parallax necessary?
Many stars are too far away to show any stellar parallax.
A class G2 V is about ______ times as luminous as the sun
1
A class G2 V is ______ times the radius of the sun.
1
What observations are necessary to determine the masses of the stars in a binary system?
the orbital period of the system and the distance between the stars
How do astronomers determine the masses of stars in a binary?
with Newton’s version of Kepler’s third law
Which of the statements below is true for the different kinds of binary stars?
It is impossible to determine the inclination of a spectroscopic binary system.
Do the stars on the main sequence illustrate the mass-luminosity relationship?
Yes, because more massive stars tend to burn hotter and brighter.
Why is it difficult to find out how common the most luminous stars are?
because they are rare
Why is it difficult to find out how common the least luminous stars are?
because most of them are so dim
The above stars are all members of the same cluster, so what do they all have in common?
approximate distance from us
What color are the brightest stars in the cluster? Some stars in the cluster have evolved off the main sequence.
red
The brightest blue-white stars in the cluster are:
red giants
What are the strengths of the Balmer lines in stellar spectra?
It depends on the temperature of the star
Where are Balmer lines strongest?
in medium temperature stars
In hot stars, which of the following is true?
Balmer lines are weak because electrons are often in higher orbits.
In cool stars, which of the following is true?
Balmer lines are weak because electrons are often not excited.
What is true of stellar spectra?
They are dark-line spectra.
What do stellar spectra tell us about a star?
both temperature and composition
What information do we get from stellar spectra?
It tells us mainly about the star’s photospheric surface.
Which star on the Spectrial Classes table would have the peak strength of ionized calcium lines as shown in the figure above?
Arcturus
Note the
line in the above spectra. It is strongest in which type of star?
A
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?
peak wavelength and temperature
In which type of star in the graph above is the sodium line strongest?
M
The broadest dark lines in the above spectra correspond to __________ in the graph below of intensity vs. wavelength of the spectral types.
the wavelength of the deepest dips
The Doppler effect can cause spectral lines to do which of the following?
All of these choices are correct.
Doppler broadening can be caused by which of the following?
very-fast-moving molecules in a star and rapid rotation of a star
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?
Barnard’s star, Sirius B, Sun, Canopus, Rigel A
Which of the following stars from the above H-R diagram has the hottest photosphere?:
Rigel A
Which of the following stars from the above H-R diagram is largest?
Antares
Which of the following stars from the above H-R diagram is most massive?
Spica A
Which of the type of stars below (all of about the same mass) is the most luminous (brightest)?
supergiant
Stars with which of the following colors have the hottest photosphere?
blue
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.)
1.3-50 pc
