binary-lab-2-Completed.docx

# To investigate eclipsing binaries further go to the

• Lab Report
• 8

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To investigate eclipsing binaries further, go to the Nebraska Astronomy Applet Project’s eclipsing binary lab at . Click on “Eclipsing Binary Simulator (swf)” in the “MAIN CONTENT” section. The screen should look something like this:

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LAB ACTIVITY UNDERSTANDING BINARY STARS SET THE LONGITUDE TO 0.0 (this is the slider directly under the picture of the stars) SET THE INCLINATION TO 90.00 (this is the slider directly under the longitude slider) SET THE ECCENTRICITY TO 0.00 (this is the slider on the bottom right of the page) LOOK AT THE DIAGRAM ABOVE. The two stars (the orangish one and the bluish one) are orbiting each other, and we are seeing this system “edge-on”. The graph on the top right shows the AMOUNT OF LIGHT received by our telescopes as time goes on. The technical term for this kind of graph is a LIGHT CURVE. When one star passes in front of the other, the total amount of light we receive goes down. Hence the ECLIPSING part of eclipsing binary. At the moment indicated, the two stars are separated and so we are receiving their combined light. However, if the animation begins, there will be a very sharp decrease in light. In fact, MOST of the light in the system will be blocked.
LAB ACTIVITY UNDERSTANDING BINARY STARS WHICH STAR IS GOING TO PASS IN FRONT WHEN THIS HAPPENS? a. The orangish star will pass in front of the blueish star first b. The bluish star will pass in front of the orangish star first c. There is no way to tell How do you know? Because the blueish star is hotter and more luminous than the organish star so when the orange star passes the blue it is blocking more light. The simulator has a number of “presets”. Take some time to become familiar with Example 1 and Example 2. What parameters are different in Example 2 (as compared to Example 1)? One star is 2x bigger than in E1. What effect does this difference have on the observed light curve? The light curve no longer has a pointy dip but a more horizontal square type dip. We’ve looked only at binary stars with perfectly circular orbits (e = 0.0), as seen perfectly edge-on (inclination = 90.0). Reality is rarely so convenient. Go to Preset Example 1. Change the eccentricity (bottom right slider) to e = 0.6. What effect does this change have on the observed light curve? It moves over to the right and includes a second pointy dip. Leaving the eccentricity at 0.6, change the radius of star 1 to 0.30 and change the radius of star 2 to its maximum allowed level. NOW what effect does this change have on the observed light curve? It has no dips in it. It is a straight horizontal line. Explore with changing the inclination, masses, radii, temperatures, and eccentricity. PART IV While binary systems are quite common, it is less common to be able to visually observe both stars in a binary system or even witness the special alignment required for an eclipse. Typically, even through a telescope, it is not possible to resolve the two individual stars as one. (This is similar to the headlights of a car. When the car is far away, the two headlines appear as one.) Fortunately, astronomers have another way of detecting binary systems. As you determined in the previous section, as the stars orbit around one another, they move through an orbit. Depending on how that orbit is oriented relative to us, the stars can sometimes move towards us and away from us.

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• Spring '16
• Nelson,D.

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