Using the Web

1.
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Go to the European Space Agency’s Gaia (Global Astrometric Interferometer for Astrophysics) mission website (http://www.esa.int/Our_Activities/Space_Science/Gaia_overview). Has Gaia been launched? How will it help astronomers determine the distances to more stars? Why will it map the stars from an L2 orbit (see Connections 4.2)?
2.
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Go to the Eclipsing Binary Stars Lab website at http://astro.unl.edu/naap/ebs/ebs.html. Click on “Eclipsing Binary Simulator.” Select preset Example 1, in which the two stars are identical. The animation will run with inclination 90° and show a 50 percent eclipse. What happens when you slowly change your viewing angle to the system—the inclination; how does this change the eclipse? At what value of inclination do you no longer see eclipses? What does the system look like at 0°? Reset the inclination to 90° and adjust the separation of the two stars. How does the light curve change when the separation is larger or smaller? Now make the two stars different. Change star 2 so that its radius is 3.0 R and its temperature is 4000 K. At what value of inclination do you no longer see eclipses? What types of eclipsing binary systems do you think are the easiest to detect?
3.
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Go to the Kepler home page (http://kepler.nasa.gov) and mouse over “Confirmed Planets” on the upper right. How many eclipsing binary stars has Kepler found? Go to the Kepler Eclipsing Binary Catalog (http://keplerebs.villanova.edu) to see what new observations look like. Pick a few stars to study. What is the inclination (“sin i”)? Look at the last column (“Figures”). The “raw” and “dtr” figures are pretty rough, but the “fit” figure shows a familiar light curve. How deep is the eclipse; that is, by what percentage does the normalized flux change during the eclipse?
4.
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Do a search for a photo of your favorite constellation (or go outside and take a picture yourself). Can you see different colors in the stars? What do the colors tell you about the surface temperatures of the stars? From your picture, can you tell which are the three brightest stars in the constellation? These stars will be named “alpha” (α), “beta” (β), and “gamma” (γ) for that constellation. Look up the constellation online and see if you chose the right stars. What are their temperatures and luminosities? What are their distances?
5.
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Go to the Spectral Types of Stars website (http://www.jb.man.ac.uk/distance/life/sample/java/spectype/specplot.htm) and run the applet provided. Note that the wavelengths are given in angstroms (Å), where 1 Å = 0.1 nm. On the right side-hand, use the menu to pull up (blue) spectra of stars from type O5 to type M5. “Fiducial wavelength” tells you where the applet will try to get the spectra to match with the (red) blackbody curve; it is set initially at 5,000 Å. Start with the O5 star and adjust the slider. What temperature blackbody curve gives you the best fit? Do the same for the other stars. Are the temperatures about what you expect? Explain why the blackbody curves seem to fit the longer wavelengths better than the shorter ones. If the observed (blue) spectra had come from space observations instead of from Earth observations, how might you expect the fit to look different?

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