Namesake star
1 Type II: W Virginis Cepheids are from older low-metallicity stars and are about 4 times less luminous than Type I. Below is the light curve of a W Virginis Cepheid from the Hipparcos database of variable stars. 2  Note the differences in the shape of the light curve.  Cepheid variable stars are the name for a special type of variable star first discovered in the constellation Cepheus. Cepheids are extremely important to astronomers because their periodic changes in brightness can be used to figure out how far away they are.  There is another class of variable star called a W. Virginis Cepheid which is about 4 times less luminous. They are from older, metal-poor star populations (Population II) and are sometimes called Type II Cepheids. Named after delta-Cephei, Cepheid Variables are the most important type of variable because it has been discovered that their periods of variability are related to their absolute luminosity. Cepheid Variable Stars. Cepheid variables are types of stars that illuminate or brighten and dim with regularity. Its cycle of becoming brilliant to dim and vice-versa is called the period of fluctuation lasts for more or less than fifty days. delta Cephei. The namesake star in the very important class of stars known as Cepheid variables, this star formed part of the original study in which Henrietta Leavitt first discovered that the periods of luminosity were related to their absolute luminosity. This has proved to be an important distance measuring tool. Named after delta-Cephei, Cepheid Variables are the most important type of variable because it has been discovered that their periods of variability a Cepheid variables are named after the star Delta Cephei, which is in the constellation of Cepheus. As is sometimes the case in the history of astronomy, this was actually the second example of this kind of variable discovered; the first was Eta Aquilae, discovered a few months earlier, in September 1784.  Classical Cepheids (also known as Population I Cepheids, type I Cepheids, or Delta Cepheid variables) undergo pulsations with very regular periods on the order of days to months. Classical Cepheids are Population I variable stars which are 4–20 times more massive than the Sun, and up to 100,000 times more luminous. Classical Cepheids and type II Cepheids follow different period-luminosity relationships. The luminosity of type II Cepheids is, on average, less than classical Cepheids by about 1.5 magnitudes (but still brighter than RR Lyrae stars). The term Cepheid originates from Delta Cephei in the constellation Cepheus, the first star of this type identified, by John Goodricke in 1784. Classical Cepheids and type II Cepheids follow different period-luminosity relationships. The luminosity of type II Cepheids is, on average, less than classical Cepheids by about 1.5 magnitudes (but still brighter than RR Lyrae stars). Type II Cepheids (also termed Population II Cepheids) are population II variable stars which pulsate with periods typically between 1 and 50 days. Type II Cepheids are typically metal-poor, old (~10 Gyr), low mass objects (~half the mass of the Sun). Classical Cepheids and type II Cepheids follow different period-luminosity relationships. The luminosity of type II Cepheids is, on average, less than classical Cepheids by about 1.5 magnitudes (but still brighter than RR Lyrae stars). Classical Cepheids (also known as Population I Cepheids, Type I Cepheids, or Delta Cephei variables) pulsate with very regular periods of the order of days to months. Classical Cepheids are population I variable stars which are 4–20 times more massive than the Sun, and up to 100,000 times more luminous. Type II Cepheids (also termed Population II Cepheids) are population II variable stars which pulsate with periods between 1 and 50 days. Type II Cepheids are typically metal-poor, old (~10 giga years), low mass objects (~half the mass of the Sun). Type II Cepheids are divided into several subgroups by period.
http://www.astronomynotes.com/ismnotes/s5.htm http://www.windows2universe.org/kids_space/cepheid_variable.html http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/cepheid.html http://planetfacts.org/cepheid-variable-stars/ http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/cepheid.html http://www.universetoday.com/40468/cepheid-variables/ https://en.wikipedia.org/wiki/Cepheid_variable https://en.wikipedia.org/wiki/Cepheid_variable https://en.wikipedia.org/wiki/Cepheid_variable https://simple.wikipedia.org/wiki/Cepheid_variable
what kind of stars are the cepheids