Astronomy 122 Distance Education ThirdHomework 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. 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 Video Tutorial for instructions

    If the above doesn't work try the One posted on YouTube

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

    In this problem, there are three unknown spectral type stars: X1, X2, and X3. You are to use the simulation to measure the equivalent widths for the following two spectral lines:

    As explained in the video tutorial, your measurements will be very sensitive to where you place the limits that define the feature. This is the nature of measuring real data, its ambiguous and usually not straight forward.

    If one makes a small adjustment in defining the window of the line and the placement of the reference level, the "answer" changes. Its suppose to. This is a measurement - there is no exact way to determine when the feature starts and ends and where to properly place the reference level. In general, the reference level should be placed close to, but outside, the window that defines the feature.

    For each star X1, X2, and X3 you should report the equivalent width value (or the strength of the line) for both the Hydrogen and the Calcium Line that you measured from the simulation

    From that information you should also report on what you think the spectral type of the star is by comparing your values with those listed in the table below.

    Fire up the simulation and make the measurements