Cepheid in the Spiral Galaxy M100

A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. The namesake and prototype of these variables is the star Delta Cephei, discovered to be variable by John Goodricke in 1784. Image File history File links M100_cepeid. ... Image File history File links M100_cepeid. ... Spiral Galaxy M100 (also known as Messier Object 100, Messier 100, M100 or NGC 4321) is a spiral galaxy in the Coma Berenices constellation. ... Most stars are of almost constant luminosity. ... Luminosity has different meanings in several different fields of science. ... For the book and the movie with the same title refer to The Namesake. ... Prototypes or prototypical instances combine the most representative attributes of a category. ... Delta Cephei (δ Cep / δ Cephei) is a star in the constellation Cepheus. ... John Goodricke (September 17, 1764 – April 20, 1786) was an amateur astronomer. ... 1784 was a leap year starting on Thursday (see link for calendar). ...

Because of this correlation (discovered by Henrietta Swan Leavitt in 1908), a Cepheid variable can be used as a standard candle to determine the distance to its host cluster or galaxy. Since the period-luminosity relation can be calibrated with great precision using the nearest Cepheid stars, the distances found with this method are among the most accurate available. Henrietta Swan Leavitt (July 4, 1868 – December 12, 1921) was an American astronomer, as well as being deaf [1] and a Christian [2]. She was born in Lancaster, Massachusetts. ... 1908 (MCMVIII) was a leap year starting on Wednesday (link will take you to calendar). ... A standard candle is an astronomical object that has a known luminosity. ... Globular Cluster M92 in the Hercules constellation. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ...

Description

A Cepheid is usually a population I giant yellow star, pulsing regularly by expanding and contracting, resulting in a regular oscillation of its luminosity. The luminosity of cepheid stars range from 10³ to 10⁴ times that of the Sun. Because Cepheids are from population I, they are sometimes called Type I Cepheids, while the similar (but belonging to population II) W Virginis variables are known as Type II Cepheids. The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude (CM) diagram) shows the relationship between absolute magnitude, luminosity, classification, and surface temperature of stars. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... The Sun is the star at the center of our solar system. ... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... A W Virginis variable is a variable star similar to a Cepheid variable. ...

The exact mass of Cepheids with given brightness or oscillations is not known to any great precision, but astronomers hope to gather data for this from the newly-discovered third star of the Polaris system [1].

Use as a "standard candle"

The relationship between a Cepheid variable's luminosity and variability period is quite precise, and has been used as a standard candle for almost a century. This connection was discovered in 1912 by Henrietta S. Leavitt. She measured hundreds of photons of Cepheid variables and discovered a distinct period-luminosity relationship. A three-day period Cepheid has a luminosity of about 800 times the Sun. A thirty-day period Cepheid is 10,000 times as bright as the Sun. The scale has been calibrated using nearby Cepheid stars, for which the distance was already known. This high luminosity, and the precision with which their distance can be estimated, makes Cepheid stars the ideal standard candle to measure the distance of clusters and external galaxies. Of course, a small error will be present because we do not know the precise location of the Cepheid variable within the cluster or galaxy. This error is typically small enough to be irrelevant in these kinds of measurements. Because of relatively high luminosity, Cepheid stars are visible from great distances. Edwin Hubble first identified some Cepheids in the Andromeda galaxy, thus proving its extragalactic nature (not known at that time). More recently, the Hubble Space Telescope succeeded in identifying some Cepheid stars in the Virgo cluster, at a distance of 60 million light years. A standard candle is an astronomical object that has a known luminosity. ... The Sun is the star at the center of our solar system. ... Edwin Hubble Edwin Powell Hubble (November 20, 1889–September 28, 1953) was an American astronomer, noted for his discovery of galaxies beyond the Milky Way and the cosmological redshift. ... The Andromeda Galaxy (also known as Messier 31, M31, or NGC 224; older texts often call it the Andromeda Nebula) is an ordinary spiral galaxy approximately 2. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth. ... A sky field near some of the brighter galaxies in the Virgo cluster. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ...

Period-Luminosity Relationship

The empirically derived relationship between a Cepheid variable's period, P (in days), and its absolute magnitude M_v is given by In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us (in the absence of interstellar extinction!). It allows the overall brightnesses of objects to be compared without regard to distance. ...

This relationship is derived from data collected from Cepheids whose distances are determined by other means.

Notes

• Some Cepheid stars (for example Polaris), have shown a decrease in their oscillation over a period of a few tens of years, and now are virtually constant.
• Cepheid stars are sometimes divided into two types, type I Cepheid and type II Cepheid. The latter type, composed of Population II stars, are now usually called W Virginis variables, and show a similar behaviour.

Polaris (α UMi / α Ursae Minoris / Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor. ... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... A W Virginis variable is a variable star similar to a Cepheid variable. ...

Examples

Some Cepheid variables with fairly bright apparent magnitudes and variations in brightness large enough to easily distinguish with the naked eye include Eta Aquilae, Zeta Geminorum, Beta Doradus, as well as the prototype Delta Cephei. // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... A naked eye is a figure of speech, referring to human visual perception unaided by enhancing equipment such as a telescope or binoculars. ... Eta Aquilae (η Aql / η Aquilae) is a star in the constellation Aquila. ... Zeta Geminorum (ζ Gem / ζ Geminorum) is a star in the constellation Gemini. ... Delta Cephei (δ Cep / δ Cephei) is a star in the constellation Cepheus. ...

See also

• Hubble constant
• RR Lyrae variable
• W Virginis variable

Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ... Hertzsprung-Russell diagram adapted from Powell. ... A W Virginis variable is a variable star similar to a Cepheid variable. ...

References

• SEDS: Variable Stars
• Leavitt, H 1908, Annals of Harvard College Observatory, vol. LX, no. 4, p. 107