exam two questions Flashcards
The most abundant elements in stars are
hydrogen and helium
Spectral lines of hydrogen are strongest in _____ stars.
A
The spectra of stars show that stars are made
of the same atoms as the Earth but in different amounts.
What are the standard units for luminosity?`
watts
Knowing only the color of a star, we can estimate the star’s
temperature.
The most abundant chemical elements in a star’s atmosphere always give the strongest spectral lines in the star’s visible spectrum.
false
If star A has twice the radius of star B, the surface area of star A is
four times the area of star B
Three stars each radiate the same amount of energy per second. They are of spectral types O (bluish), G (yellow), and K (orange). Rank them in order of their radii
O is smallest, K is largest
Analysis of the light curve of an eclipsing binary star may give the astronomer information about
the diameters of the two component stars
In a spectroscopic binary system, the star showing the larger blue shift is:
less massive and approaching us at this moment.
In a visual binary system with circular orbits, if in 20 years the two stars’ position angles have shifted by 30 degrees, the pair’s period must be:
240 years
If Star A is closer to us than Star B, then Star A’s parallax angle is
larger than that of Star B
On an H-R diagram, stellar masses
can be determined for main-sequence stars but not for other types of stars.
Each choice below lists a spectral type and luminosity class for a star. Which one is a red supergiant?
spectral type M2, luminosity class I
If a star has a parallax of 0.05”, then its distance in light years is about:
65 light years
On a Hertzsprung-Russell diagram, where would we find stars that are cool and luminous?
upper right
A nearby star has a parallax of 0.2 arc seconds. What is its distance?
5 parsecs
What is the primary visible color of an emission nebula?
red due to ionized hydrogen atoms
Ionization of hydrogen in H II regions is most visible at:
656.3 nm, Balmer alpha line for 3-2 electron transition.
A reflection nebula is caused by
starlight scattered by dust particles.
If you wanted to observe stars behind a molecular cloud, in what wavelength of light would you most likely observe?
infrared
Neutral hydrogen is most obvious in the electromagnetic spectrum:
at 21 cm in the radio region.
When an electron in H changes its spin from the same to the opposite direction as the proton, it:
emits a radio wave photon
All globular clusters in our Milky Way are about how old?
around ten billion years old
On an H-R diagram, a protostar would be:
above and to the right of the main sequence.
During a protostar’s T Tauri phase, it:
may develop very strong winds
What is the approximate range of masses that newborn main-sequence stars can have?
0.1 to 150 solar masses
Which of the following phenomena is not commonly associated with the star formation process?
intense ultraviolet radiation coming from a protostar
The spectrum of a planetary nebula shows ___ because it ____ its central star
emission lines; is ionized by
which of the following best describes the evolutionary track followed on the H-R diagram for the most massive stars?
horizontally right
If you had something the size of a sugar cube that was made of neutron star matter, it would weigh
about as much as a large mountain.
Most of the energy of the supernova is carried outward via a flood of:
neutrinos.
The making of abundant iron nuclei is typical of:
type II supernovae.
Pulsars:
spin very rapidly when they’re young.
Which of these does NOT depend on a close binary system to occur?
a Type II supernova
A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?
nova
If a star is rapidly rotating on its axis, its rotation can cause lines in its spectrum to
be more spread out
Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?
Calculate the star’s luminosity if we know its distance, or calculate its distance if we know its luminosity.
The spectral sequence in order of decreasing temperature is
OBAFGKM
A star whose surface is hotter than another star’s appears
bluer
In general, the narrower the spectral line of a star:
bluer
A star’s luminosity is the
total amount of light that the star radiates each second.
The radius of a star can be determined from knowledge of its luminosity and surface temperature. Radii can also be measured directly for the components of
eclipsing binaries.
In what range of masses are most stars found?
.1 to 100 solar masses
A spectroscopic binary is a double star showing a periodic variation in
radial velocity
The most important reason for studying binary stars is to find
the masses of stars.
A hypothetical visual binary is observed to have a period of 3 years and a semi major axis of 3 A.U. The sum of the masses for the system
3 solar masses
On the H-R diagram, red supergiants like Betelguese lie:
at the top right.
A main sequence star at spectral type K0 is _____ than a K0 giant star
smaller and more dense
If a star appears to move back and forth relative to other stars over a six-month period, this motion is due to the star’s:
parallax shift
most of the stars on the H-R diagram belong to which group?
main sequence
Star A is a main sequence star of spectral type F2 and star B is a white dwarf of spectral type B4. Which statement below is correct
Star B is hotter than star A.
On an H-R diagram, stellar radii
increase diagonally from the lower left to the upper right.
A “fuzzy” dark or light patch in the sky is called a:
nebula
What effect do even thin clouds of dust have on light passing through them?
It dims and reddens the light of all more distant stars.
Interstellar dust consists mostly of
microscopic particles of carbon and silicon.
What are the very cold (about 20 K), dense clouds of gas thought to be the most massive objects in the Galaxy called?
molecular clouds
What two things are needed to create an emission nebulae?
hot stars and interstellar gas, particularly hydrogen
A large gas cloud in the interstellar medium that contains several type O and B stars would appear to us as:
an emission nebula
Most stars, probably all stars, formed:
in a cluster of stars.
The vast majority of stars in a newly formed star cluster are
less massive than the Sun.
What is the force that keeps a main sequence star from blowing apart?
gravitation
A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy?
from the release of gravitational energy as the protostar continues to shrink
Approximately what core temperature is required before hydrogen fusion can begin in a star?
10 million K
No stars have been found with masses greater than 300 times our Sun because
they would generate so much power that they would blow themselves apart.
What is the source of the large dust shells seen around some red giants and red supergiants?
material from winds from these same stars
Which of the following statements about stages of nuclear burning (i.e., first-stage hydrogen burning, second-stage helium burning, etc.) in a massive star is not true?
Each successive stage lasts for approximately the same amount of time.
As a 10 solar mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity:
remains roughly constant.
A solar mass star will evolve off the main sequence when:
it builds up a core of inert helium.
The core of a highly evolved high mass star is a little larger than:
Earth.
Nearly all the elements found in nature were formed inside stars, EXCEPT for:
hydrogen and helium.
Neutron stars do NOT have:
rotation periods comparable to the Sun’s.
When a high-mass star becomes a supernova, it is probably a result of
its core collapsing
Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true?
Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars
Supernova explosions are important because they seem to be
the main way of releasing heavy atoms into space
