Cepheid

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Related to Cepheids: Period-luminosity relationship, Delta Cepheid

Cepheid

(see -fee-id) short for Cepheid variable.

Cepheid

 

a type of variable star with a periodic variation of brightness (with an amplitude ranging from 0.1 to 2 stellar magnitudes) caused by the pulsation of the star’s outer layers. The name was derived from the prototype variable star—δ Cephei.

Classical, or ordinary, cepheids (type I cepheids) include su-pergiants of spectral classes F and G; the periods of variation of their brightness range from one to 50 days, occasionally reaching 218 days. Both the mass and luminosity of classical cepheids increase with the period, and the more massive cepheids are also younger. The distinct relationship between the periods of light variation and luminosity makes it possible to determine, for the observed period and apparent stellar magnitude, the distances to cepheids, as well as to the star clusters and galaxies in which they are located, up to 3–4 megaparsecs. Cepheids thus serve as indicators of intergalactic distances. The period-age relation is used to investigate the modes of star formation in galaxies. Given the same period of light variation, W Virginis variables, which are classified as cepheids (type II cepheids), are two stellar magnitudes fainter than classical cepheids. Short-period cepheids are sometimes called RR Lyrae variables.

REFERENCES

Pul’siruiushchie zvezdy. Moscow, 1970.
Iavleniia nestatsionarnosti izvezdnaia evoliutsiia. Moscow, 1974.

IU. N. EFREMOV

Cepheid

[′sē·fē·əd]
(astronomy)
One of a subgroup of periodic variable stars whose brightness does not remain constant with time and whose period of variation is a function of intrinsic mean brightness.
References in periodicals archive ?
Knowing that the luminosity of any star appears to fall off in proportion to the square of its distance from Earth, researchers can in theory calculate the separation between any galaxy containing cepheids and our own.
Since telescopes can only resolve individual stars in relatively nearby galaxies, astronomers can't use cepheids to obtain direct measures of the distance of faraway bodies, which would offer a truer value for the expansion rate of the universe.
For this study, Stanek, Bird and Ohio State doctoral student Jose Prieto uncovered 18 ULP cepheids from the literature.
The distances to these nearby galaxies are well known, so the astronomers used that knowledge to calibrate the distance to the ULP cepheids.
They found that they could use ULP cepheids to determine distance with a 10-20 percent error - a rate typical of other methods that make up the cosmic distance ladder.
Calculating the true brightness of a Cepheid depends ultimately on the distance to one of our galaxy's closest neighbors, the Large Magellanic Cloud.
Even if the masers move in elliptical orbits, rather than in circles, as the team supposed, a discrepancy with the Cepheid distance still holds, he adds.
In the absence of a cosmic yardstick, astronomers use so-called standard candies,, especially a group of yellowish, blinking stars called Cepheid variables.
This revision, in turn, increases the distances to nearby galaxies containing Cepheids by about 10 percent, Feast reported at the London meeting.
By measuring the period of a Cepheid and its apparent brightness, astronomers can deduce the distance to the star and to the galaxy in which it resides.
Huchra of Harvard, recently announced that they had used the repaired Hubble Space Telescope to identify and study several dozen Cepheids in a spiral member of the Virgo cluster called M100.
Or, as Michael Rowan-Robinson of Imperial College in London told a group of astronomers in Edinburgh last April, "Detecting Cepheids in Virgo would settle the distancescale controversy.