115 terms

Evolution of stars

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The hydrogen lines in spectral type A stars
are most narrow for supergiants.
Parallax would be easier to measure if
Earth's orbit were larger.
Absolute visual magnitude is
the apparent magnitude of a star observed from a distance of 10 pc.
A star's luminosity depends only on the star's
temperature and diameter.
In an H-R Diagram, stars with the smallest radius are found in the __________ of the diagram.
lower left corner
In the H-R diagram, 90 percent of all stars are
on the main sequence.
We know that giant stars are larger in diameter than the sun because
they are more luminous but have about the same temperature.
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.
Compared with the spectral lines in the solar spectrum, lines in a supergiant spectrum are
more narrow.
The most common stars are
lower main sequence stars.
The __________ of a star is a measure of the total energy radiated by the star in one second.
luminosity
Sheat is an M2 II star. 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.
d Circini is an O 8.5 V star. Based on this information which of the following are true?
II. d Circini has a diameter that is greater than that of the sun.
III. d Circini is more luminous than the sun.
IV. d Circini is located near the upper left hand corner in the HR diagram.
To determine the period of a visual binary, we must measure
position
In a binary system, the more massive star
is nearest the center of mass.
Spectroscopic binaries are difficult to analyze because
we can't see the shape of the orbit.
Which star in Figure 8-1 above is most like the sun?
HR 5337
Which star in Figure 8-1 above has the greatest surface temperature?
Alnilam
Which of the stars in Figure 8-1 above has the largest absolute visual magnitude?
Sirius B
An eclipsing binary will
always be a spectroscopic binary.
If we can solve the orbital motion of an eclipsing binary, we can find
a. the masses of the stars.
b. the diameters of the stars.
Which of the following best obey the mass-luminosity relation?
main sequence stars
Which of the following stars is most dense?
a white dwarf
A spectroscopic binary shows periodic variations in its
radial velocity.
Stars on the main sequence with the greatest mass
are spectral type O stars.
The star Algol is
an eclipsing binary.
The total mass of a binary system can be calculated from
the semi major axis and period of the orbit.
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?
1 to 2
If a star has a parallax of 0.02 seconds of arc, then its distance is
50 pc
If a star with an absolute magnitude of -5 has an apparent magnitude of +5, then its distance is
1000 pc
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.
Star A has a mass of 22.3 solar mass and star B has a mass of 3.7 solar masses.
What is the total mass of a binary star system with P = 20 yr and a = 10 AU?
2.5 solar masses
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?
Star B is twice the mass of star A.
In the light curve below, what is the period of the binary?
32.5 days
At what point in the light curve below is the cool star in front of the hotter star?
4
Which star in Table 8-1 above would appear the faintest in the night sky?
65 Tau
Which star in Table 8-1 above has the greatest luminosity?
58 Ori
Which star in Table 8-1 above is the closest to Earth?
HR 2491
Which star in Table 8-1 above has the greatest surface temperature?
HR 4621
Which star in Table 8-1 above has the greatest diameter?
58 Ori
Which star in Table 8-2 above is the closest to Earth?
9 CMa
Which star in Table 8-2 above has the greatest surface temperature?
d Cen
Which star in Table 8-2 above has the greatest diameter?
HD 39801
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?
700,000 km
A 2 solar mass star on the main sequence would have a luminosity of approximately __________ solar luminosities.
11
Protostars are difficult to observe because
a. the protostar stage is very short.
b. they are surrounded by cocoons of gas and dust.
c. they radiate mainly in the infrared.
d. all of the above
e. they are all so far away that the light hasn't reached us yet.
The nuclear reactions in a star's core remain under control so long as
pressure depends on temperature.
Interstellar gas clouds may collapse to form stars if they
encounter a shock wave.
_________ are small luminous nebulae excited by nearby young stars.
Herbig-Haro objects
Opacity is
a measure of the ease with which photons can pass through a gas.
The Great Nebula in Orion
is an emission nebula.
. __________ is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence.
The CNO cycle
The diagram below is an HR diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star?
4
In the proton-proton chain
energy is produced in the form of gamma rays and the velocity of the created nuclei.
The carbon-nitrogen-oxygen cycle
combines four hydrogen nuclei to form one helium nucleus, which produces energy.
What causes the outward pressure that balances the inward pull of
gravity in a star?
The outward flow of energy.
The free-fall contraction of a molecular cloud
can be initiated by shock waves from supernovae.
Convection is important in stars because it
b. mixes the gases of the star.
c. transports energy outward in the star.
__________ occurs when most of the material collapsing to form a protostar has fallen into a disk around the star and a strong wind from the warm protostar ejects material from its poles.
A bipolar flow
Which of the following is not evidence of the existence of an interstellar medium?
molecular bands in the spectra of cool stars
Molecular clouds can be observed
using radio telescopes to observe the CO emission from the clouds.
The main sequence has a limit at the lower end because
there is a minimum temperature for hydrogen fusion.
There is a mass-luminosity relation because
stars support their weight by making energy.
Due to the dust in the interstellar medium, a star will appear to an observer on Earth to be
fainter and cooler than it really is.
The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
0.08 M .
What is the lifetime of a 10 M star on the main sequence?
3.2 x 107 years
__________ require(s) that a young hot star (T 25,000 K) be relatively nearby
Emission nebulae
The extinction of starlight due to the interstellar medium
II. is the greatest in the infrared.
IV. is caused by dust particles.
______ are small dark nebulae about 1 light-year in diameter that contain 10 to 1,000 solar masses.
Bok globules
Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because
the lines are extremely narrow.
Stars are born in
dense molecular clouds.
Absorption lines due to interstellar gas
are more narrow than the lines from stars because the gas has a lower pressure than stars.
As a star exhausts hydrogen in its core, it
becomes cooler and more luminous.
A star will experience a helium flash if
its core is degenerate when helium ignites.
In degenerate matter
pressure does not depend on temperature.
Giant and supergiant stars are rare because
the giant and supergiant stage is very short.
Star cluster are important to our study of stars because
they give us a method to test the our theories and models of stellar evolution.
What is the approximate age of the star cluster in the diagram below?
10 billion years
The triple alpha process
occurs during helium flash.
The lowest mass object that can initiate thermonuclear fusion of hydrogen has a mass of about
0.08 M .
Which of the following nuclear fuels does a one solar mass star use over the course of its entire evolution?
hydrogen and helium
Helium flash occurs
because degenerate electrons in the core do not allow the core to expand as it heats up.
Stars in a star cluster
a. all have the same age.
b. all have the same chemical composition.
If the stars at the turnoff point of a cluster have a mass of 3 M , what is the age of the cluster?
6.4 x108 years
In the diagram below, which point indicates the location on the HR diagram of a one solar mass star when it undergoes helium flash?
5
The lowest-mass stars cannot become giants because
they cannot heat their centers hot enough.
A planetary nebula is
the expelled outer envelope of a medium mass star.
The Chandrasekhar limit tells us that
not all stars will end up as white dwarfs.
A Type I supernova is believed to occur when
a white dwarf exceeds the Chandrasekhar limit.
Massive stars cannot generate energy through iron fusion because
iron is the most tightly bound of all nuclei.
The theory that the collapse of a massive star's iron core produces neutrinos was supported by
the detection of neutrinos from the supernova of 1987.
Synchrotron radiation is produced by
high-velocity electrons moving through a magnetic field.
A nova is almost always associated with
a white dwarf in a close binary system
The Algol paradox is explained by considering
mass transfer between the two stars in a binary system.
Stars with masses between 0.4 M and 4 M
undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
A type-II supernova
c. is characterized by a spectrum that shows hydrogen lines.
d. occurs when the iron core of a massive star collapses.
Synchrotron radiation is produced
in supernova remnants.
When material expanding away from a star in a binary system reaches the Roche surface
the material is no longer gravitationally bound to the star.
A white dwarf is composed of
carbon and oxygen nuclei and degenerate electrons.
A planetary nebula
produces an emission spectrum.
If the theory that novae occur in close binary systems is correct, then novae should
repeat after some interval.
As a white dwarf cools its radius will not change because
pressure does not depend on temperature for a white dwarf because the electrons are degenerate.
The diagram below shows a light curve from a supernova. How many days after maximum light did it take for the supernova to decrease in brightness by a factor of 100?
150
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
+5.14
A G2 I star is____ in diameter and_____ luminous than the sun.
Larger
More
_______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.
Spectroscopic parallax
Luminosity class IV objects are known as
Subgiants
The masses and diameters of each star in the binary can be determined from______binaries
Eclipsing
If we divide the mass of a star by its volume we calculate the star's
Average density
The condition of_________ means that the force due to gravity pushing down on a layer is exactly equal to the pressure pushing outward on that layer.
Hydrostatic equilibrium
Stars with masses greater than 1.1 solar masses use the________to convert hydrogen into helium and produce energy
CNO cycle
Energy transport by________ is important when photons cannot readily travel through a gas.
Convection
___________appear reddish in color due to the light emitted by the Balmer series of the hydrogen atom.
Emission nebulae or HII regions
The pressure of an interstellar gas cloud depends on the clouds______ and ______
Temperature
Density
A gas in which the pressure no longer depends on the temperature of the gas is said to be
Degenerate