Emily AliceaMuoz

1
Cepheid variable stars as distance indicators

• Emily Alicea-Muñoz
• 24 November 2003

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What are Cepheid variables?

• Radially pulsating giant stars
• Upper instability strip in the HR Diagram
• Changes in Temperature, Radius, Magnitude,
  Luminosity
• Mass range 3 M - 18 M
• Luminosity range 102 L 104 L
• Period range 1d - 50d
• Average MV range -0.5 (dimmest) to -6.0
  (brightest)
• Spectral class range F6 (hottest) to K2 (coldest)

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Delta Cephei

• Magnitude and radial velocity curves are mirror
  images of each other
• Star is brighter when expanding outward, after
  passing through minimum radius
• Spectral type changes from F5 to G2
• Temperature variation of 1500 K

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Period-Luminosity Relationship

• Discovered by Henrietta
• Leavitt in 1912
• Brighter Cepheids have
• longer periods
• Sandage Tammann
• (1968) determined
• Color dependence
• Instability strip has finite width ? color
  dependence
• Feast Walker (1987)

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Distance indicators

• Method for distance determination
• Measure apparent magnitude (mV)
• Measure period (P) in days
• Determine absolute magnitude (MV) from P-L
  relationship
• Calculate distance modulus (mV - MV)
• Range of distances
• Ground-based observations 4 Mpc
• HST 20 Mpc (circa Virgo Cluster)

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Problems and future work

• Problems
• Metallicities metal-poor Cepheids appear redder
• Extinction makes the Cepheids look dimmer
• Reddening changes the color measured for
  Cepheids outside our Galaxy
• Zero-point calibration precise parallax
  measurements of nearby Cepheids needed to
  determine the constants in the formulas for P-L
  or P-L-C relationships
• Future work
• Tammann, Sandage Reindl (2003) are working on a
  new P-L-C relation in a 3-paper series

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References

• Carroll Ostlie. An Introduction to Modern
  Astrophysics. Addison-Wesley, 1996. Chapters 14
  and 25
• Feast, M.W. 1999. PASP, 111, 775
• Feast Walker. 1987. ARAA, 25, 345
• Kaufmann Freedman. Universe. 5th edition. W.H.
  Freeman and Company, 1999. Chapters 21 and 26
• Ryden, B. Introduction to Cosmology.
  Addison-Wesley, 2003. Chapter 7
• Sandage Tammann. 1968. ApJ, 151, 531
• Tammann, Sandage Reindl. 2003. AA, 404, 423
• Zeilik Gregory. Introductory Astronomy
  Astrophysics. 4th edition. Saunders College
  Publishing, 1998. Chapters 18 and 22
• Cepheid animations in title slide taken from
• http//www.phys.ufl.edu/buchler/ceph/anim.html
• http//www.eso.org/outreach/eduoff/catchastar/CAS2
  002/cas-projects/germany_cephei_1/haupt.htm