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. 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.



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

    L α M4

    (in words this means that luminosity is poportional to Mass to the 4th power)

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

    Show your work in answering these three questions:



  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 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?

  5. Stars are often born in stellar clusters. Below are two simulated images to a cluster, one is taken in Blue light and one is taken in Red light.

    There are 31 stars in this cluster. Extremely blue stars would be much brighter in the blue frame than the red frame where as extremely red stars would be much brighter in the red frame than the blue frame.

    Compare the Red and Blue frames linked below and identify, by their star number, the three bluest and three reddest stars in this cluster. Select an exposure time of 30 seconds for both the red and blue frames.