ASTR 122 Distance Education Third Homework

  1. Describe the major differences between Globular Clusters and Open Clusters. Where in our galaxy are Globular clusters likely to be located and where are open clusters likely to be found. Attach an image of each kind of cluster to your submitted homework.



  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. 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 -- its probably best to right click and save the WMV file on our desktop and open it up with Windows Media Player,

    Note: an older non video tutorial can be found here but try an access the video one

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

    In this problem, you are to use the simulation to measure the equivalent widths for the following spectral lines:

    You are to report those measurements using the spectral measurement tool as described in the video and tutorial above. Note that 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. To help with this you are also to enter in the wavelengths of what you chose for the start and end of the feature in the report table. That wavelength is the number that is in the rectangular box. In some cases there will be no spectral feature at the indicated wavelength so no measurement can be made.

    As an example, the image below shows a measurement of the 4340 Hydrogen line for some star.

    So for this case:

    Now, if one makes a small adjustment in defining the window of the line and the placement of the referene 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. So you can see in the image below that I now obtain an "answer" of 3.0 (instead of 3.4) for the strength of the line when I slightly change the location of the window and the reference point. This is why there is a range of values in the comparison table below.

    Report Table Is Downloadable Here. Submit your work when your done.

    After you have made your measurements for the three stars, X1,X2 and X3, you need to compare them against the table of values that is in Module 2, Lecture D. From that comparison, enter in the spectral type that you think corresponds to each individual star in the last column of the worksheet. For your convenience, that table is shown below:

    The Actual Simulation to work with