Homeworks 12

Review for the Final on 12/11/2009

Mini-Quizzes

Lecture ?

1. How long does sunlight take to get to the next star?
   • 8 minutes
2. How long is a typical galaxy
   • 10,000 Lys
3. In azimutal coordinates, the positions of star change due to
   • the rotation of the Earth
4. Peticular velocity is the projected velocity of
   • a star relative to other stars

Lecture 6

1. Yearly parallax of a star is 0.1 arcsec. What is its distance?
   • 10
2. The electric and gravitational --- (in Newton's limit) are both scalar
3. Absolute magnitude is
   • the measure of luminosity of an object
4. Light is both particle and wave because otherwise
   • atoms would not be stable

Lecture 8

1. Besides the radio, ground-based observatories allow to observe in the wavelength range of
   • optical to infrared
2. By photometry of astronomical object, we measure
   • the apparent brightness
3. Which of the following effects limit the imaging in reflector telescopes in prime focus?
   • spherical aberration
   • chroma
   • chromatic aberration

Lecture 12

1. A white dwarf star is dimmer than a main sequence star of the same temperature by a factor of
   • 10⁴
2. Radii of white dwarf stars are smaller than main sequence stars by
   • 100
3. For gray atmospheres the temperature of the black body radiation emitted is equal to temperature atmosphere by depth of
   • $T^{4}=T_{eq}^{4}{\tfrac {3}{4}}(T+{\tfrac {2}{3}})$
4. Electrons can be excited from a lower state j to a higher state i by
   • ... photon absorption?

Lecture 15

1. Variations in stellar spectra are mainly due to changes of the (pick one):
   • stellar radius
   • stellar mass
   • effective temperature
   • none of the above
2. Spectra of M stars are dominated by lines of:
   • Neutral moles and molecules
3. Hot stars show weaker Hydrogen lines in the optical spectra because
   • H is mostly ionized
4. Cool stars show weaker hydrogen lines in the optical spectra because (pick one):
   • Metal lines dominate
   • H is mostly...
   • Most of the electrons are in the ground state

Midterm 1

The test consists of a combination of multiple choice questions and other questions which count for 1/3 and 2/3 of the scores, respectively. For partial credit, feel free to add a sentence for the multiple choice questions, and write down the individual steps.

Problem 1A

The proper motion of a star is caused by

• (a) The earth orbiting the sun
• (b) The velocity of the star relative to us
• (c) The orbit of a star within a binary system
• (d) The transverse velocity of the star relative to us

Problem 1B

How are continuum, absorption, and emission line spectra produced? Name the basic types of transitions in an atom. Name one physical process for each of them. Name 2 classes of astronomical objects for each of them.

Problem 2A

Other than the equations for microscopic physics (EOS, nuclear reactions, atomic physics), the basic equations of stellar structure are (mark all which apply):

• (a) Newton's laws
• (b) Pressure equilibrium
• (c) Conservation of mass
• (d) Wave equation
• (e) Momentum transport
• (f) Energy generation
• (g) Energy transport

Problem 3A

Suppose two stars 1 and 2 are identical in every respect but star 2 is 100 times further away. If the apparent magnitude of star 1 is 10 mag, the apparent magnitude of star 2 is:

• (a) 0
• (b) 5
• (c) 10
• (d) 15
• (e) 20

The answer is NOT (b).

Problem 4A

A white dwarf star is smaller than a main sequence star of the same effective temperature by a factor of:

• (a) 1
• (b) 10^-2
• (c) 10¹
• (d) 10^-4
• (e) 10^-3

Problem 5A

Two stars A and B have the same temperature, but their absolute brightnesses are 0 and +5 mag, respectively. Star A is brighter than Star B by a factor of:

• (a) 0.01
• (b) 0.1
• (c) 1
• (d) 10
• (e) 100

The answer is NOT (a) or (b)