2) Calculate the total mass of a binary system which has a period of 5 yrs and average separation of 4.2 AU. Assume one of the stars is an F0V star (as determined by its spectrum) while the other is a stellar corpse too dim to see. Based on your calculation and the info from the table above, what is the mass of the corpse? What kind of corpse is it? Now assume the system has an inclination angle between 45-89 degrees (pick some random number that your classmates are unlikely to choose). What is the new calculated mass for the corpse? Has this changed your identification? Explain.
3) Imagine that we lived in a universe where helium is inherently unstable and falls apart as soon as it is made (half-life far less than a second) and the dominant fusion cycle is 3H à Li. How would this affect what we observe in the universe? Be creative and thoughtful in your answer. Geology, astronomy, biology, and chemistry may figure in your answer. And no, Chuck Norris cannot force alpha particles to form!
4) For the following 2 questions, each of you is being assigned a different main sequence star:
Ashley – B5
Matt – A0
Mike K – A5
Zach – F0
Keith – F5
Carrie – K0
Mike Z – K5
Naomi – M0
For your respective star, calculate the following:
Average density
Central pressure
Central temperature
Lifetime (years)
Luminosity (relative to sun)
Apparent mag at a distance of 100 pc
Compare your answers to someone one else in the class (preferably with a really different type of star) and comment on the differences noted.
5) Devise your own method of defining the spectral class of your star using the relative strengths of 3 different spectral lines using this diagram (the one in your book isn't detailed enough)
For example, a hypothetical class compares the strengths of lines from MgII, FeII, and TiO (I picked a combination that makes no sense because there is no overlap. Your three lines should overlap on the diagram). The definition of this class is that the MgII line is twice as strong as the FeII line and the TiO line is 1/3 the strength of the MgII line.
Have a classmate check your work on this question and make sure your definition is precise and unique (can only be used to define YOUR spectral class and no other).
An important note: although Annie Cannon did her classes by eyeball, the method you are using in this problem is precisely the method astronomers now use to define these classes!
6) A star has a proper motion of 2" per year and parallax of 0.03". A 610 nm hydrogen line appears in this star's spectrum at 612 nm. Calculate as much information as you can about this star given these observations. If the parallax has an uncertainty of 10%, which of your calculations will be affected?
7) The distance to a star is found through trigonometric parallax to be 710 pc, through spectroscopic parallax to be 730 pc, and because this star is a Cepheid, the period-luminosity relation gives a distance of 750 pc. Comment on the possible sources of error/uncertainty in each measurement. In the end, which one do you think we should "trust"? Why?
8) For the star you were assigned above, calculate the bending of starlight for a lightbeam just grazing the surface of the star, as well as the gravitational redshift at the surface of the star. Discuss the ease or difficulty in measuring your results.
9) A star is discovered which has no elements heavier than helium present in its spectrum. Can we be certain we have discovered a pop III star? What other explanation might there be for this lack of spectral lines?
10) You are the head of a research team which looks for planets through spectroscopic doppler effects. Your equipment is sensitive enough to find v/V values of 1/2000. A reporter asks you if your experiment can find "earths" around sunlike stars. Can you? If not, what would the sensitivity of your experiment have to be to do so?
KL 3/18/08