Chapter 11 and 12

[1] Short Answer Questions (10 points; 2 points for each lettered subheading):

(a) What is the temperature of the Sun at its surface?

What is the temperature of the Sun at its core?

(b) What type (frequency) of photon is generated at the core of the Sun.

How long between the polarity reversals (pole flips) of the Sun’s magnetic field?

(c) How long does it take the Sun to Rotate once around at the equator?

How long does it take the Sun to Rotate once around at the poles?

(d) The Sun generates energy by fusing what into what?

Approximately, how much longer before the Sun swells and cooks Earth.

(e) How long does it take the radiant energy generated in the Sun’s core to migrate to the surface
of the Sun?

How many Earths would line up end to end across the diameter of the Sun? Do not google it!
(Hint: Divide the radius of the Sun by the radius of the Earth in the same units). Voila!

[2] (10 points)
Describe thoroughly the Proton – Proton chain of fusion by which the Sun generates radiant energy
through the production of 𝛾- ray photons deep in the core. Show all the steps.
Hint: This question is answered for you completely in animation 11.1 page 383.

[3] (10 points)
Explain the hydrostatic equilibrium within a star. If a star were to accumulate more mass from say gas
transfer from a close binary companion star describe in detail the way the mass receiving star would
respond in order to maintain hydrostatic equilibrium? How would the donor star respond to maintain
equilibrium?

[4] (10 points)
Describe a Hertzsprung-Russell diagram.
What is plotted vertically?
What is plotted horizontally?
Because of Wein’s law, what is (equivalently) plotted horizontally?
Where are the largest radius stars located on an HR diagram?
Where are the smallest radius stars located on an HR diagram?

As you progress along the main sequence from the lower right to the upper left:
How does stellar mass change?
How does stellar life expectancy change?

[5] (10 points)
Two stars orbit with period of 915 days. They are separated by 6.05×10^8 km. What is their combined
mass?
Hint: See Astronomer’s Toolbox 12-4 page 412.
Hint: 1 𝑎𝑢 = 1.5 × 10! 𝑘𝑚.
(show all work)

[Extra Points] (5 points)
Use the inverse square law for light intensity to find the luminosity for the star Antares, given that its
known distance from parallax measurements is 170 parsecs, and its intensity measured at Earth is
8.4 × 10″!𝑊/𝑚#.

1 𝑃𝑎𝑟𝑠𝑒𝑐 = 3.086 × 10$% 𝑚𝑒𝑡𝑒𝑟𝑠

Hint: See Canvas/Modules/Chapter 11 and 12/Standard Candles and the Inverse Square Law.

𝐼 = 𝐿
4𝜋𝑑#

How many times more luminous is Antares than our Sun?

[Bonus Extra points] (5 points)
Sirius (A) has white dwarf companion star Sirius (B). The system is known to have a semi-major axis of 20
au and a period of 50 years. Doppler shifts show that at any given time Sirius (B) moves twice as fast as
Sirius (A). What is the mass of Sirius (A)? What is the mass of Sirius (B)?
Hint: conservation momentum requires that 𝑚&𝑣&= 𝑚’𝑣’. Solve for the ratio of the masses.
Kepler’s third will yield the sum of the masses of the two stars. Together you can find the mass of each
star.