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CEPHEIDS

CEPHEIDS. What are Cepheids?. Stars that “pulse” and change luminosity Very bright (100,000x luminosity of Sun) Used to measure extreme distances in space Their brightness and pulsing allows for measurements to distant galaxies. Cepheids- history.

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CEPHEIDS

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  1. CEPHEIDS

  2. What are Cepheids? • Stars that “pulse” and change luminosity • Very bright (100,000x luminosity of Sun) • Used to measure extreme distances in space • Their brightness and pulsing allows for measurements to distant galaxies

  3. Cepheids- history • First discovered by John Goodricke in 1784 • Named after the first star (Delta Cephi) in the constellation Cepheus (the King) • Was not known at that time the important significance they would play • Henrietta Leavitt (1912) studied over 500 Cepheids in the Magellanic Cloud Henrietta Swan Leavitt

  4. History- continued • Harlow Shapely (1915) charted size of Milky Way using Cepheids • Leavitt and Shapely determined that the period of a Cepheid varied directly with its luminosity- (i.e., the brightest Cepheids have the longest periods) • Edwin Hubble’s work with Cepheids settled the debate of whether the Milky Way represented the entire universe, or was merely one galaxy of many

  5. Cepheid Characteristics • “Classical Cepheids” are Yellow Super Giants • Drifted off the main sequence into the “instability zone” • Pulsation is an actual change in temperature and diameter of the star • Typically ~25% change in size • Classical Cepheids are 4-20x more massive than the Sun, and 100,000x or more brighter pulsating stars

  6. HR diagram showing location of Cepheid variables compared to main sequence stars "HR-diag-instability-strip" by Rursus - Own work.

  7. Classical vs. Type II Cepheids • Type II Cepheids (AKA Population II Cepheids) are: • Metal-poor • Old stars • Smaller than the Sun (~1/2 solar mass) • Further subdivided by period length (1-4 days, 5-10 days, 10-20 days, 20+ days)

  8. Cepheids Graphs • Remember the direct relationship: the longer the period, the brighter the Cepheid

  9. Cepheids Graphs • What is the period of the Cepheid in this graph?

  10. Nearest Cepheid • Our nearest Cepheid is Polaris (See location on HR Diagram) • Classified as a classical Type I Cepheid • Recent evidence has shown Polaris is more than 100 light years closer than previously thought Polaris Closer Than Thought

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