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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
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.
lab 14 the period luminosity relation

Lab 14: The Period-Luminosity Relation

Tiffany Pewett

pewett@chara.gsu.edu

cepheid variables
Cepheid Variables
  • Yellow Supergiant stars.
  • Are pulsating.
    • This causes them to become brighter and fainter over time.
    • They have extremely regular (& predictable) periods!
types
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!
using cepheids
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!
procedure
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.
procedure1
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!
final answers
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.