Cepheid

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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 ?
Cepheids, also referred to as pulsating stars for their ability to throb in brightness over a regular cycle, are monitored to gauge their precise brightness and the data is then compared with what is visible from Earth to work out a distance.
Despite this, finding Cepheids in the inner Milky Way is difficult, as the Galaxy is full of interstellar dust which blocks out light and hides many stars from view.
Fernie of David Dunlap Observatory, [states] that a very well-known Cepheid variable star, RU Camelopardalis, has recently ceased to pulsate and now appears to be practically constant in brightness
Until now, all known galactic Cepheids were no farther than 28,000 light-years away; these five are almost three times as far.
We found ultra-long period cepheids to be a potentially powerful distance indicator.
This portion of the electromagnetic spectrum has numerous advantages, especially when observing Cepheid variable stars, the so-called "standard candles" that are used to determine distances to distant galaxies.
The nice feature about Cepheids is that they have this instability which permits them to function as a huge amplifier," Learned says.
This fact was obscured among the stars nearer to us, because some Cepheids seem dim only because they are quite far away, while others seem bright only because they are near.
Cepheids tests consist of totally automated GeneXpert systems, which are intended to enable rapid, sophisticated genetic testing and give test results for the management of infectious diseases, among clinical applications.
The astronomers hoped the four stars were Cepheids, standard candles that regularly expand and contract at a rate directly related to their intrinsic brightness.
Since Polaris is the nearest Cepheid variable star to our solar system, an accurate distance to the star could serve as a benchmark for measurements of other Cepheids used to determine the scale of the universe.
Glenn Wahlgren, Spitzer program scientist at NASA Headquarters in Washington, said infrared vision, which sees through dust to provide better views of variable stars called cepheids, enabled Spitzer to improve on past measurements of the Hubble constant.