Classical Cepheid variable

Hertzsprung–Russell diagram showing the location of several types of variable stars superimposed on a display of the different luminosity classes.

Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude up to about 2 magnitudes. Classical Cepheids are also known as Population I Cepheids, Type I Cepheids, and Delta Cepheid variables.

There exists a well-defined relationship between a classical Cepheid variable's luminosity and pulsation period,[1][2] securing Cepheids as viable standard candles for establishing the galactic and extragalactic distance scales.[3][4][5][6] Hubble Space Telescope (HST) observations of classical Cepheid variables have enabled firmer constraints on Hubble's law, which describes the expansion rate of the observable Universe.[3][4][6][7][8] Classical Cepheids have also been used to clarify many characteristics of our galaxy, such as the local spiral arm structure and the Sun's distance from the galactic plane.[5]

Around 800 classical Cepheids are known in the Milky Way galaxy, out of an expected total of over 6,000. Several thousand more are known in the Magellanic Clouds, with more discovered in other galaxies;[9] the Hubble Space Telescope has identified some in NGC 4603, which is 100 million light years distant.[10]

  1. ^ Udalski, A.; Soszynski, I.; Szymanski, M.; Kubiak, M.; Pietrzynski, G.; Wozniak, P.; Zebrun, K. (1999). "The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. IV. Catalog of Cepheids from the Large Magellanic Cloud". Acta Astronomica. 49: 223–317. arXiv:astro-ph/9908317. Bibcode:1999AcA....49..223U.
  2. ^ Cite error: The named reference OGLE_1 was invoked but never defined (see the help page).
  3. ^ a b Freedman, Wendy L.; Madore, Barry F.; Gibson, Brad K.; Ferrarese, Laura; Kelson, Daniel D.; Sakai, Shoko; Mould, Jeremy R.; Kennicutt, Robert C.; Ford, Holland C.; Graham, John A.; Huchra, John P.; Hughes, Shaun M. G.; Illingworth, Garth D.; Macri, Lucas M.; Stetson, Peter B. (2001). "Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant". The Astrophysical Journal. 553 (1): 47–72. arXiv:astro-ph/0012376. Bibcode:2001ApJ...553...47F. doi:10.1086/320638. S2CID 119097691.
  4. ^ a b Cite error: The named reference tammannsandage2008 was invoked but never defined (see the help page).
  5. ^ a b Majaess, D. J.; Turner, D. G.; Lane, D. J. (2009). "Characteristics of the Galaxy according to Cepheids". Monthly Notices of the Royal Astronomical Society. 398 (1): 263–270. arXiv:0903.4206. Bibcode:2009MNRAS.398..263M. doi:10.1111/j.1365-2966.2009.15096.x. S2CID 14316644.
  6. ^ a b Freedman, Wendy L.; Madore, Barry F. (2010). "The Hubble Constant". Annual Review of Astronomy and Astrophysics. 48: 673–710. arXiv:1004.1856. Bibcode:2010ARA&A..48..673F. doi:10.1146/annurev-astro-082708-101829. S2CID 13909389.
  7. ^ Cite error: The named reference ngeow2006 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference macririess2009 was invoked but never defined (see the help page).
  9. ^ Szabados, L. (2003). "Cepheids: Observational properties, binarity and GAIA". GAIA Spectroscopy: Science and Technology. 298: 237. Bibcode:2003ASPC..298..237S.
  10. ^ Newman, J. A.; Zepf, S. E.; Davis, M.; Freedman, W. L.; Madore, B. F.; Stetson, P. B.; Silbermann, N.; Phelps, R. (1999). "A Cepheid Distance to NGC 4603 in Centaurus". The Astrophysical Journal. 523 (2): 506. arXiv:astro-ph/9904368. Bibcode:1999ApJ...523..506N. doi:10.1086/307764. S2CID 15343736.