Cepheid variable

CepheidCepheidsCepheid variablesCepheid variable starsCEPCepheid and Cepheid-like starsCepheid classCepheid distance scaleCepheid Period-Luminosity relationshipCepheid Stars
A Cepheid variable is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.wikipedia
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Henrietta Swan Leavitt

Henrietta LeavittH. LeavittLeavitt, Henrietta Swan
This robust characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds.
This work led her to discover the relation between the luminosity and the period of Cepheid variables.

Classical Cepheid variable

classical Cepheidδ Cep variableclassical Cepheids
Cepheid variables are divided into two subclasses which exhibit markedly different masses, ages, and evolutionary histories: classical Cepheids and type II Cepheids.
Classical Cepheids (also known as Population I Cepheids, Type I Cepheids, or Delta Cepheid variables) are a type of Cepheid variable star.

Instability strip

Cepheid instability stripradialradial pulsations
A Cepheid variable is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. Delta Scuti variables are A-type stars on or near the main sequence at the lower end of the instability strip and were originally referred to as dwarf Cepheids.
The unqualified term instability strip usually refers to a region of the Hertzsprung–Russell diagram largely occupied by several related classes of pulsating variable stars: Delta Scuti variables, SX Phoenicis variables, and rapidly oscillating Ap stars (roAps) near the main sequence; RR Lyrae variables where it intersects the horizontal branch; and the Cepheid variables where it crosses the supergiants.

Cosmic distance ladder

standard candlestandard candlesdistance
A strong direct relationship between a Cepheid variable's luminosity and pulsation period established Cepheids as important indicators of cosmic benchmarks for scaling galactic and extragalactic distances.
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.

Star

starsstellarmassive star
A Cepheid variable is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.
In the Local Supercluster it is possible to see star clusters, and current telescopes could in principle observe faint individual stars in the Local Group (see Cepheids).

Type II Cepheid

type II Cepheidstype II Cepheid variable
Cepheid variables are divided into two subclasses which exhibit markedly different masses, ages, and evolutionary histories: classical Cepheids and type II Cepheids.
Like all Cepheid variables, Type IIs exhibit a relationship between the star's luminosity and pulsation period, making them useful as standard candles for establishing distances where little other data is available

Period-luminosity relation

period-luminosity relationshiprelationshipLeavitt's law
A strong direct relationship between a Cepheid variable's luminosity and pulsation period established Cepheids as important indicators of cosmic benchmarks for scaling galactic and extragalactic distances.
Using the simplifying assumption that all of the Cepheids within the Small Magellanic Cloud were at approximately the same distance, the apparent magnitude of each star is equivalent to its absolute magnitude offset by a fixed quantity depending on that distance.

Delta Cephei

δ Cepδ Cephei
The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, the first of its type to be so identified.
It is the prototype of the Cepheid variable stars that undergo periodic changes in luminosity.

Cepheus (constellation)

CepheusCefeoCep
The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, the first of its type to be so identified.
Delta Cephei is the prototype Cepheid variable, a yellow-hued supergiant star 980 light-years from Earth.

Delta Scuti variable

δ Sct variableDelta Scuti typeDelta Scuti
Delta Scuti variables are A-type stars on or near the main sequence at the lower end of the instability strip and were originally referred to as dwarf Cepheids.
The variables follow a period-luminosity relation in certain passbands like other standard candles such as Cepheids.

John Goodricke

Goodricke, John
The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, the first of its type to be so identified.
Goodricke is credited with discovering the periodic variation of β Lyrae and δ Cephei, the prototypical example of the Cepheid variable stars.

RR Lyrae variable

RR Lyr variableRR LyraeRR Lyrae variables
RR Lyrae variables have short periods and lie on the instability strip where it crosses the horizontal branch.
(In fact, Walter Baade's failure to find them in the Andromeda Galaxy led him to suspect that the galaxy was much farther away than predicted, to reconsider the calibration of Cepheid variables, and to propose the concept of stellar populations.

Edwin Hubble

HubbleEdwin P. HubbleEdwin Powell Hubble
In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the Andromeda Nebula, and showed that the variables were not members of the Milky Way.
He used the strong direct relationship between a classical Cepheid variable's luminosity and pulsation period (discovered in 1908 by Henrietta Swan Leavitt ) for scaling galactic and extragalactic distances.

Globular cluster

globular clustersglobulartidal radius
Type II Cepheids are used to establish the distance to the Galactic Center, globular clusters, and galaxies.
He examined the RR Lyrae variables in the clusters (which he assumed were Cepheid variables) and used their period–luminosity relationship for distance estimates.

Ejnar Hertzsprung

HertzsprungE. HertzsprungHertzsprung, Ejnar
In 1913, Ejnar Hertzsprung attempted to find distances to 13 Cepheids using the motion through the sky.
In 1913 he determined the distances to several Cepheid variable stars by parallax, and was thus able to calibrate the relationship, discovered by Henrietta Leavitt, between Cepheid period and luminosity.

HD 84810

l Carl CarinaeI Carinae
These Cepheids are yellow bright giants and 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.
l Carinae is classified as a Cepheid variable star and its brightness varies over an amplitude range of 0.725 in magnitude with a long period of 35.560 days.

Harlow Shapley

Shapley, HarlowH. ShapleyShapley
In 1915, Harlow Shapley used Cepheids to place initial constraints on the size and shape of the Milky Way, and of the placement of our Sun within it.
The astronomical issues were soon resolved in favor of Curtis' position when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy.

RS Puppis

RS Pup
Uncertainties have diminished over the years, due in part to discoveries such as RS Puppis.
RS Puppis (or RS Pup) is a Cepheid variable star around 6,000 ly away in the constellation of Puppis.

RV Tauri variable

RV Tau variableRV TauriRV Tauri star
Stars with periods between 1 and 4 days are of the BL Her subclass, 10–20 days belong to the W Virginis subclass, and stars with periods greater than 20 days belong to the RV Tauri subclass.
They exhibit relationships between their periods, masses, and luminosity, although not with the precision of more conventional Cepheid variables.

Andromeda Galaxy

AndromedaM31Andromeda Nebula
In 1924, Edwin Hubble established the distance to classical Cepheid variables in the Andromeda Galaxy, until then known as the Andromeda Nebula, and showed that the variables were not members of the Milky Way.
The estimated distance of the Andromeda Galaxy from our own was doubled in 1953 when it was discovered that there is another, dimmer type of Cepheid.

Walter Baade

W. BaadeBaadeBaade, Walter
In the 1940s, Walter Baade recognized two separate populations of Cepheids (classical and type II).
The same observations led him to discover that there are two types of Cepheid variable stars.

Hubble's law

Hubble constantHubble parameterHubble flow
Classical Cepheids are used to determine distances to galaxies within the Local Group and beyond, and are a means by which the Hubble constant can be established.
His observations of Cepheid variable stars in “spiral nebulae” enabled him to calculate the distances to these objects.

Galaxy

galaxiesgalacticgalactic nuclei
Type II Cepheids are used to establish the distance to the Galactic Center, globular clusters, and galaxies.
Using the new 100 inch Mt. Wilson telescope, Edwin Hubble was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.

Sergei Alexandrovich Zhevakin

S. A. Zhevakin
The mechanics of the pulsation as a heat-engine was proposed in 1917 by Arthur Stanley Eddington (who wrote at length on the dynamics of Cepheids), but it was not until 1953 that S. A. Zhevakin identified ionized helium as a likely valve for the engine.
Zhevakin is credited for identifying ionized helium as the valve for the heat engine that drives the pulsation of Cepheid variable stars.

Polaris

North Starpole starNorthern Star
It is the first classical Cepheid to have a mass determined from its orbit.