QUIZ 2 YOUR NAME:___

Possibly useful formulae:

Doppler Shift: ;      Distance(parsecs)

Stephan's Law: Energy/area Temp ;     Intensity

1. Star A and Star B have the same trigonometric parallax and the apparent brightness of A is four times that of B. (Assume no dust toward either star)

   a) What are their relative distances b) what are their relative luminosities?

2. What two quantities are plotted in a H-R diagram?

   ___ stellar apparent brightness vs. stellar distance

   ___ stellar luminosity vs. stellar distance

   ___ stellar apparent brightness vs. stellar surface temperature

   ___ none of these

3. Why are the hydrogen absorption lines very weak in the spectrum of a cool red giant?

   ___ Red giants have very little hydrogen in their atmospheres

   ___ Most of the hydrogen has been ionized in these cool stars

   ___ Most of the hydrogen atoms have their electrons in the ground state and therefore can't absorb visible light photons

   ___ This is another of Bolte's trick questions - the coolest stars have the strongest hydrogen absorption lines

4. What is the distance to a star whose trigonometric parallax is 0.1 arcsec?

   ___ 0.1 parsec

   ___ 10 parsec

   ___ 10 light-years

   ___ it depends on the amount of dust between us and the star

5. Suppose that we moved the Sun ten times further away than its current distance.

   a) How would the apparent brightness of the Sun change? b) How would the luminosity of the Sun change?

6. Let's think about two stars. Star A has a surface temperature of 5000K, Star B has a surface temperature of 10000K.

   a) Compare the energy generated per unit surface area for these two stars. b) If Star A is the same luminosity as star B, compare the relative sizes (either surface area or radius, but specify which) of the two stars.

7. Star C and Star D have identical spectra. If Star C is brighter than Star D, which of the following are true, which are false?

   ___ Star C is more luminous than Star D

   ___ Star C and Star D have the same temperature

   ___ Star D is more distant than Star C

   ___ Star C must be a giant

8. For main-sequence stars in the Hertzsprung-Russell Diagram:

   a) Compare the luminosities of Star E and Star F if Star E has a higher surface temperature and twice the distance of Star F. b) Compare the masses of Star E and Star F from part (a).

9. Suppose you take a spectrum of a ``star'' on 10 different nights and discover see the spectral lines from an A star and the spectral lines from a K star and the lines appear at different wavelengths on the different nights.

   a) What type of system is this very likely to be? b) What property of stars can be measured from such systems?

10. What is the most important stellar properity that determines the strength of the Hydrogen absorption lines?

    ___ The surface temperature of the star

    ___ The chemical composition of the star

    ___ The amount of interstellar reddening in the direction of the star

    ___ The size of the telescope used to observe the star