Sunday, January 30, 2011

Optional module 9

Send a screen shot of the HR diagram to Chris Martin and calculate the distance to the open cluster.

2 comments:

  1. Pheeeeewwwww! Ok, here it goes. This was a BIG one, but even MORE enlightening than all the others. I even tried it with my 8 physics students, and they actually were able to stumble through it with my limited help-ability.

    First of all, a few points of clarification. I ‘often’ had to refer back to modules 6, 7 and 8 to remind myself how to do things. Things like setting brightness/contrast (the auto button works well) selecting aperture sizes and making sure that the sky annulus is checked to show on the image. I enjoyed finding out how to stack images and then being able to scroll (on the mouse) between the two images to take measurements. I needed to take measurements on one image (v-filter) and then take measurements on the same star in the other image (b-filter) – that way the data stayed relatively organized.
    On the spreadsheet I simply copied and pasted all the data from measurements into one column. Then, went back and matched up in neighboring column each star’s data. I inserted a formula to convert flux to magnitude and placed these values in columns to the right of the data. I then calculated (with a formula) the B-V value. To graph these took a bit of work. It wasn’t quite as easy as plotting the H-R Diagram in Module 6, I had to make sure that my Y-axis (Vmagnitude) was reverse order, I had to adjust the axis limits (to fit my data) and most difficult was I had to make sure that the B-V was on the X-axis and the V was on the Y-axis. I then copied the data for main sequence stars and graphed these values on the same graph. Using an overhead transparency sheet I copied my data points and the axis onto the transparency, slid it to match (by guessing) over the Standard curve. I just slid my graph (dots for the data for this cluster) over the standard graph (on the paper behind) and looked for a best fit match. I had to then determine the Apparent Magnitude (my value for V) with the Absolute Magnitude (the Standard value for V) as the graphs matched up (I just looked at the Y axes and saw where they matched up to find these values) and I also had to estimate the reddening that occurs which shifted my graph left/right (for this I just looked at the difference between my x=0 and the standard graph on the paper behind. This was tough, but it can be done.
    I studied the open cluster M34 and calculated the distance to be 975 LightYears. The value in astronomical reference books is about 1400 LY.

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  2. It is, indeed, a very long assignment. I analyzed 65 stars and stopped when I had what I felt was reasonable coverage of the graph that I made.

    I recommend not brushing away the circles from using the aperture tool because it's a little cool to see how many of the stars you've analyzed in a cluster. I did M26.

    I actually did much of this analysis (or, at least, much of the reasonable portion of this analysis) sitting in Kathy's office so that might be a good place to relocate yourself if you're at the end stage of this project. By lining up the curve of the main sequence stars in the plot you made with the main sequence stars on the graph in Figure 2 (or 4, but...in either case, the first figure after table 1) you can discover what the B-V offset is. And by comparison of the y axis you can discover the M_apparent - M_absolute value. Using the equation in section 3.3 I calculated the number of parsecs to be 4742 parsecs. (That's using a B-V value of .2 and a M_apparent - M_absolute value of 14. This is about 15,445 light years.

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