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Announcements

Announcements. Projects due in 2 ½ weeks!! On-campus observing rescheduled for July 16 th , this may move to the 15 th or 17 th depending on weather ! Powerpoints : 20 info slides. Papers: 4.5 info pages. Lab 14: The Period-Luminosity Relation. Tiffany Pewett pewett@chara.gsu.edu.

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Announcements

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  1. Announcements • Projects due in 2 ½ weeks!! • On-campus observing rescheduled for July 16th, this may move to the 15th or 17th depending on weather! • Powerpoints: 20 info slides. Papers: 4.5 info pages.

  2. Lab 14: The Period-Luminosity Relation Tiffany Pewett pewett@chara.gsu.edu

  3. Cepheid Variables • Yellow Supergiant stars. • Are pulsating. • This causes them to become brighter and fainter over time. • They have extremely regular (& predictable) periods!

  4. Cepheid Properties

  5. Cepheid Pulsations

  6. Types • There are 2 types of Cepheid Variables. • We will only be working with classical Cepheids • The two types show 2 different, strong relationships between their pulsation periods and their luminosity!

  7. Types

  8. Using Cepheids • They are extremely useful for finding accurate distances to far off galaxies! • Since they are very bright they are easy to spot. • Period LuminosityDistance!

  9. Using Cepheids

  10. Using Cepheids

  11. Procedure • First, make sure you carefully read and follow the lab procedure! • Fill in the blank column on Table I first! • Use the equation: M= m+5-(5×log(2600pc)) • On Figure 1 plot all points from Table I & II, you are plotting logP& M. • This is your P-L relation! • Use a ruler to help you plot, if needed.

  12. Procedure • Draw astraightline (using a ruler) through your cluster of points on Figure 1. • Note: This line will NOT go through your origin! • On Figure 2 plot all 25 points from Table III. • When done, draw a“best-fit”curve through your points, your peaks need to be the same height!

  13. Final Answers • Follow the procedure closely and fill in all answers! • m= 15.556 (you will have gotten this by averaging all mag values from Table III). • P is the time passed between your two peaks. • Find M using your plot on Figure 1. • Find D using the provided graph on Figure 3.

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