Astronomy 122 Distance Education Third Homework Assignment

  1. Explain why measuring parallax distances for only the brightest appearing stars in the sky would give you a biased luminosity scale and an unrepresentative sample of stars.



  2. Find some information about the white dwarf cooling curve. What is the principal way that a white dwarf looses its energy? How can the cooling curve be used to to determine the age of our Galaxy.



  3. Explain the overall concept of pressure support (against gravity) in stars and why stars are unstable if they are not generating energy in their cores.



  4. For low mass stars, the relation between their luminosity (intrinsic energy output) and their mass is the following:

    L α M4
    (Luminosity is proportional to mass to the fourth power)

    A one solar mass star has a luminosity of one solar luminosity.

    Show your work

    a) what is the luminosity of a 4 solar mass star compared to a 1 solar mass star?

    b) The lifetime of a star is basically mass divided by luminosity (M/L). This is because L = rate of fuel usage and M = mass of fuel; divide the two to get a fuel lifetime.
    example: If I have 10 kg of gas in my tank and use gas at the rate of 5 kg per hour then I can drive for 2 hours before I have exhausted the fuel.

    If the main sequence lifetime of a one solar mass star is 10 billion years show, using the above scaling, that the main sequence lifetime of a 4 solar mass star would be about a few hundred million years.

  5. Measuring Real Stellar Specta

    In this exercise, you will be measuring the equivalent widths of absorption lines in real spectra of real stars.

    Before using the simulation , please refer to this YouTube Tutorial

    If you DO NOT DO USE THIS TUTORIAL, you will likely be lost

    Fire up the simulation and make the measurements

    Comparing the Hydrogen Line Strength of two stars.

    Submit screen shots of both of your measurements (a and b below) for this exercise

    a) From the list under step 1 choose the star type labelled A5-7V and measure the equivalent width of the Hydrogen line at 4860 angstroms.

    b) Now make the same measurement of the star G8IV

    c) why was the measurement more difficult for the G8IV star?