Exercise 1 Finding A Cepheid Variable Star Before We Can Use Cepheids To Measure The Distance To Andromeda We First Ne 1 (76.66 KiB) Viewed 52 times
Exercise 1 Finding A Cepheid Variable Star Before We Can Use Cepheids To Measure The Distance To Andromeda We First Ne 2 (62.97 KiB) Viewed 52 times
Exercise 1: Finding a Cepheid variable star Before we can use Cepheids to measure the distance to Andromeda, we first need to find one of these stars inside that galaxy. This is tricky: when we take a single image with a telescope, Cepheids look just like any other star. To identify a Cepheid we need to take lots of images of a galaxy over many days, and then comparing these to see if any of the stars change in brightness. We have a series of images that will let us do just this. Using a very powerful telescope, many digital photographs were taken of a small region in the Andromeda galaxy, roughly one every half hour, every night for three weeks. These images have been loaded into the two flash programs linked on Blackboard. The first program is the Blink Comparator Simulator. This program flicks through these images, almost like a cartoon, to allow you to see changes in any of the stars. Open the Blink Comparator Simulator in the NAAP Labs software. Load the first image by clicking the "add" button in the right-hand "Blinking Queue Controls" panel. Now the left-hand "Blink Comparator" panel should show a field of stars. This is our small patch of the Andromeda Galaxy, and one of these stars is a Cepheid variable. We just need to figure out which one! To the right is a list of images (under "Observation List"). Each image shows the same patch of the galaxy, but taken at different times. The time at which each image was taken is called its epoch. The epoch number is in units of days, so the first image was taken at time 1.7215 days (that's 1.7215 days after time = 0 days which isn't shown here). The second image was taken around half an hour after the first at time = 1.7422 days. The last image is around 22 days after the first.
In the "Blinking Queue Controls" panel, load all of the images into the blinker. You can do this as follows: click on the second image, scroll down to the end of the observations list, then hold the shift key and click on the last image. All items in the list should turn blue. Now click on "add". The blinking queue on the right should fill up. Important: move the "rate" sliding scale all the way to the right to blink as fast as possible. Now click the "blink" button. In the image to the left you should see that a few of stars are flickering. Not all of these are Cepheid variables! We want the star in the lower right quarter of the image that is flickering. This one is a Cepheid. Place your cursor over the Cepheid variable and record its x & y coordinates. (If you don't see the coordinates above your cursor, make sure "show crosshairs" is checked below the image.) Your coordinates should have an x value larger than 200 and a y value larger than 150. If not, you have the wrong star. Keep looking! Cepheid variable star coordinates: x = , y = We also need to find a star that is not flickering to use as a comparison star for the next section. We will use the brightest star in the top left-hand quarter of the image. Go ahead and record its coordinates. Comparison star coordinates: x = y =
Join a community of subject matter experts. Register for FREE to view solutions, replies, and use search function. Request answer by replying!