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Cepheids and stars
In the Local Supercluster it is possible to see star clusters, and current telescopes could in principle observe faint individual stars in the Local Cluster — the most distant stars resolved have up to hundred million light years away ( see Cepheids ).
More recently, this inclined geometry for field stars in the LMC has been confirmed via observations of Cepheids, core helium-burning red clump stars and the tip of the red giant branch.
A relationship between the period and luminosity for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of variable stars.
Type II Cepheids ( historically termed W Virginis stars ) have clock regular light pulsations and a luminosity relation much like the δ Cephei variables, so initially they were confused with the latter category.
Type II Cepheids stars also belong to Population II, compared to Population I of δ Cepheids, and so have a lower metallicity.
These stars are somewhat similar to Cepheids, but are not as luminous.
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 typically between 1 and 50 days.
A relationship between the period and luminosity for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of variable stars in the Magellanic Clouds.
Classical Cepheids are younger and more massive population I stars, whereas Type II Cepheids are older fainter population II stars.
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 Cepheids are a class of pulsating variable stars ; Delta Cephei has a minimum size of 40 solar diameters and a maximum size of 46 solar diameters.
They were first recognized as being distinct from classical Cepheids by Walter Baade in 1942, in a study of Cepheids in the Andromeda Galaxy that proposed that stars in that galaxy were of two populations.
In contrast to Cepheids, RR Lyraes are old, relatively low mass, metal-poor " Population II " stars.
From 1915 to the 1930s, the RR Lyraes became increasingly accepted as a class of star distinct from the Cepheids, due to their shorter periods, differing locations within the galaxy, and chemical differences from classical Cepheids, being mostly metal-poor, Population II stars.

Cepheids and They
They were once known as Dwarf Cepheids.
They are much more common than Cepheids, but also much less luminous.

Cepheids and have
Cepheids have been shown to have a relationship between their absolute luminosity and the period over which their brightness varies.
However, Cepheids appear to suffer from a metallicity effect, where Cepheids of different metallicities have different period-luminosity relations.
Classical Cepheids have also been used to clarify many characteristics of our galaxy, such as the Sun's height above the galactic plane and the Galaxy's local spiral structure.
These unresolved matters have resulted in cited values for the Hubble constant ( established from Classical Cepheids ) ranging between 60 km / s / Mpc and 80 km / s / Mpc.
The few remaining members of an intelligent non-human alien race have been removed from their dying planet and transferred to a human-occupied planet Cepheus-18 ( hence their name, Cepheids ).
By submitting reports and encouraging others to submit reports, he manages to have a fleet of huge spaceships deliver a bulky cargo for the benefit of the Cepheids.
It does however have a very different ending — the Cepheids steal the spacecraft and head for an independent life in the Magellanic Clouds.
Some other Cepheids such as Polaris are bright but have only a very small variation in brightness.

Cepheids and periods
Classical Cepheids ( or Delta Cephei variables ) are population I yellow supergiants which undergo pulsations with very regular periods on the order of days to months.
Delta Scuti ( δ Sct ) variables are similar to Cepheids but rather fainter, and with shorter periods.
Classical Cepheids ( also known as Population I Cepheids, Type I Cepheids, or Delta Cephei variables ) undergo pulsations with very regular periods on the order of days to months.
W Virginis variables are a subclass of Type II Cepheids which exhibit pulsation periods between 10 – 20 days, and are of spectral class F6 – K2.

Cepheids and months
However, the namesake for classical Cepheids is the star Delta Cephei, discovered to be variable by John Goodricke a few months later.
However, the namesake for classical Cepheids is the star Delta Cephei, discovered to be variable by John Goodricke a few months later.

Cepheids and their
Due to their common occurrence in globular clusters, they are occasionally referred to as cluster Cepheids.
The strong direct relationship between a Cepheid variable's luminosity and pulsation period secures for Cepheids their status as important standard candles for establishing the Galactic and extragalactic distance scales.
Cepheids are yellow supergiants of spectral class F6 – K2 and their radii change by (~ 25 % for the longer-period I Carinae ) millions of kilometers during a pulsation cycle.

Cepheids and luminosity
Comparing the light curve, the amplitude and the radial velocity variations as compared to the light curve, Type II Cepheids constitute a different class of star with a luminosity relation offset from that of the δ Cepheids.

Cepheids and is
Classical Cepheids, Type II Cepheids, RR Lyrae variables and Delta Scutis belong to the instability strip which is believed to be driven by Eddington pulsations in helium, while for the Beta Cepheids the pulsation mechanism is unknown.
The mechanism is believed to be Eddington pulsations, like for the yellow Cepheids ( see above ), but with molecular hydrogen as the variable opacity layer of the star instead of helium.
The accepted explanation for the pulsation of Cepheids is called the Eddington valve, or κ-mechanism, where the Greek letter κ ( kappa ) denotes gas opacity.
This statistical parallax method is useful for measuring the distances of bright stars beyond 50 parsecs and giant variable stars, including Cepheids and the RR Lyrae variables.
In the ' Second Foundation ' trilogy, a series of books authorized by the estate of Asimov, a race of Aliens within the Foundation Universe is mentioned who appear to be in circumstances similar to the Cepheids.
The stellar population includes four Cepheids and RV Tauri variables, plus at least one RR Lyrae variable for which a period is known.
As a member of the category of variable stars known as classical Cepheids, it has a regular pulsation frequency that is determined by its mass.
Along with Delta Cephei, Zeta Geminorum and Beta Doradus, it is one of the most prominent naked eye Cepheids ; that is, both the star itself and the variation in its brightness can be distinguished with the naked eye.

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