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 ?
All authors of the article, published in Science, are the University of Warsaw employees: 'A three-dimensional map of the Milky Way using classical Cepheid variable stars', D.M.
However, thanks to Cepheids, (https://www.sciencenews.org/article/3-d-map-stars-reveals-milky-way-warped-shape) all of this is now possible.
The combined measurements helped the SH0ES team refine the Cepheids' true brightness.
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.
Stars at the outer edge of the Milky Way are hard to come by, so mapping the Cepheids' locations and tracking their motions could help pinpoint how much dark matter is out there.
"We found ultra-long period cepheids to be a potentially powerful distance indicator.
"The beauty of employing Cepheids is that these stars can be seen from afar; we monitor them out through the Virgo cluster, and any developing technological society would seem to be likely to closely observe them as distance markers," he says.
Since the launch of NASA's Hubble Space Telescope in 1990, the team has observed 18 galaxies up to 65 million light years away and discovered almost 800 Cepheid variable stars, a special class of pulsating star used for accurate distance measurement.
Distances to Cepheids can be determined with an accuracy better than 5 per cent.
"However, we recently published a new catalogue of well-behaved variable stars known as classical Cepheids, for which distances as accurate as 3 to 5 per cent can be determined." That database allowed the team to develop the first accurate three-dimensional picture of our Milky Way out to its far outer regions.
Like most Cepheids it brightens faster than it fades; it takes about 1 1/3 days to swell from minimum to maximum, then 4 days to fade back down again.