If we could find the distance to a Cepheid somehow, we could derive a relationship between period and absolute magnitude which we could use as a distance indicator.
Cepheids are rare stars, and so they are typically far away and we don't have parallaxes for many..
More than 400 Cepheids are known in the Galaxy and about 1000 Cepheids have been found in each of the two nearest galaxies, the Magellanic Clouds, as well as substantial numbers in other nearby galaxies..
There is a direct relationship between the length of a Cepheid's pulsation and its true brightness.
Measuring a Cepheid's apparent brightness -- how bright it looks from Earth -- allows astronomers to calculate its true brightness, which in turn reveals its distance..
Cepheid variable stars are intrinsic variables which pulsate in a predicatable way.
In addition, a Cepheid star's period (how often it pulsates) is directly related to its luminosity or brightness.
Cepheid variables are extremely luminous and very distant ones can be observed and measured..
Cepheid variables can be used to measure distances from about 1kpc to 50 Mpc..
Cepheids are very luminous, massive variables with periods of 1 -70 days.
They are named after the first-such pulsating variable, δ Cephei discovered by John Goodricke in 1784.
Cepheid light curves are distinctive and show a rapid rise in brightness followed by a more gradual decline, shaped like a shark fin..
The classical Cepheids have periods from about 1.5 days to more than 50 days and belong to the class of relatively young stars found largely in the spiral arms of galaxies and called Population I.
Population II Cepheids are much older, less luminous, and less massive than their Population I counterparts..
Around 800 classical Cepheids are known in the Milky Way galaxy, out of an expected total of over 6,000.
Several thousand more are known in the Magellanic Clouds, with more discovered in other galaxies; the Hubble Space Telescope has identified some in NGC 4603, which is 100 million light years distant..
Classical Cepheids are comparatively young stars with masses of several times the solar mass.
This follows from their strong concentration toward the plane of the Milky Way and their low space velocities.
Their presence in star clusters allows their ages to be estimated as up to about 108 yr..
Cepheid Variables are very large, luminous, yellow stars.
They change in brightness very regularly with periods of 1 to 70 days between peaks.
The stars are called Cepheids after the first star of this type to be discovered - Delta Cephei..
There are actually two classes of Cepheid: Type I Cepheids (δ Cepheus is a classical Cepheid) are population I stars with high metallicities, and pulsation periods generally less than 10 days.
Type II Cepheids (W Virginis stars), are low-metallicity, population II stars with pulsation periods between 10 and 100 days..
Its all to do with the outer layers of the star.
The core of the star is producing heat which is absorbed by the outer layer causing the outer layer to get hot.
As the outer layer gets hot it expands and cools.
The outer layer now absorbs less radiation..
Most pulsating variable stars inhabit an instability strip on the H-R diagram.
The most luminous ones are known as Cepheid variables.
The light curve of this pulsating variable star shows that its brightness alternately rises and falls over a 50-day period..
Cepheid variables can be used to map objects in space because they pulsate between dim and bright phases over a regular span of time, usually between one and 70 days.
The period between the star's consecutive brightest points can be used to determine the star's luminosity, or brightness compared to the Sun..
I THE THEORY OF CEPHEID VARIABILITY 15 For a giant star, because of the rapid increase in density near the core of the star, the amplitude of oscillation becomes very small inside r=*Ro.
This permits the introduction of a rigid boundary at a small but finite inner radius which is outside the sources of stellar energy..
Cepheid variables have a strong correlation between their pulsation period and luminosity.
Thus, as we constrain a given Cepheids pulsation period, we can determine it's luminosity.
The distance to any object can be found if we know it's luminosity using the relationship between flux and luminosity..
Though M100 is the most distant galaxy in which Cepheid variables have been discovered, HST must find Cepheids in even more distant galaxies before accurate distances can be used to calculate a definitive size and age for the universe..
Cepheids have been extremely important as distance indicators for many years.
Although they don't all have the same average absolute magnitude as RR Lyraes do, they are more useful since they are brighter stars and can be observed at greater distances..
Cepheid variables can be seen and measured to a distance of about 20 million light years, compared to a maximum distance of about 65 light years for Earth-based parallax measurements and just over 326 light years for the ESA's Hipparcos mission..
The classical Cepheids have periods from about 1.5 days to more than 50 days and belong to the class of relatively young stars found largely in the spiral arms of galaxies and called Population I.
Population II Cepheids are much older, less luminous, and less massive than their Population I counterparts..
History.
On September 10, 1784, Edward Pigott detected the variability of Eta Aquilae, the first known representative of the class of classical Cepheid variables.
The eponymous star for classical Cepheids, Delta Cephei, was discovered to be variable by John Goodricke a few months later..
History of variable stars
The first modern identified variable star was Omicron Ceti, later renamed Mira.
It had been described as a nova in 1596 by David Fabricius.
In 1638, Johannes Holwards observed Omicron Cetipulsating in a regular 11-month cycle.Jan 28, 2015.
More than 400 Cepheids are known in the Galaxy and about 1000 Cepheids have been found in each of the two nearest galaxies, the Magellanic Clouds, as well as substantial numbers in other nearby galaxies.
The close relationship between period and luminosity which was found by Henrietta S..
This tells one the distance to the star, by comparing its known luminosity to its observed brightness.
The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784.
It was the first of its type to be identified..
The classical Cepheids, which are dependable in their period-luminosity relationship, all have periods from about 1.5 days to more than 50 days and belong to the class of relatively young stars found largely in the spiral arms of galaxies and called Population I..
In 1924 Edwin Hubble detected Cepheids in the Andromeda nebula, M31 and the Triangulum nebula M33.
Using these he determined that their distances were 900,000 and 850,000 light years respectively.
He thus established conclusively that these "spiral nebulae" were in fact other galaxies and not part of our Milky Way..
A decade after Leavitt first observed the relationship between brightness, period, and distance in Cepheid variable stars by studying variable stars in the Small Magellanic Cloud, Edwin Hubble used Cepheid variables to demonstrate that a spiral nebula lay one million light years away— and so outside the Milky Way .
Ans.
Edwin Hubble Edwin Hubble used the cepheid variabl….
Henrietta Swan Leavitt, (born July 4, 1868, Lancaster, Massachusetts, U.S.—died December 12, 1921, Cambridge, Massachusetts), American astronomer known for her discovery of the relationship between period and luminosity in Cepheid variables, pulsating stars that vary regularly in brightness in periods ranging from a .
Leavitt is best known for discovering about 2,400 variable stars between 1907 and 1921 (when she died).
She discovered that some of these stars have a consistent brightness no matter where they are located, making these so-called Cepheid variables a good measuring stick for astronomical distances..
This characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds.
The discovery allows one to know the true luminosity of a Cepheid by just observing its pulsation period..
A.C.Banerji proposed the Cepheid Hypothesis on the origin of the solar system in 1942.
He also worked on the physical theory of the oscillating universe and the method of promoting the arms of a spiral nebula..
Cepheid variable stars have proved to be one of the most valuable methods for distance determination because their period of variability has been shown to be related to their absolute luminosity by a period-luminosity relationship.
They can then be calibrated as standard candles for distance calculation..
Cepheid variables can be used to map objects in space because they pulsate between dim and bright phases over a regular span of time, usually between one and 70 days.
The period between the star's consecutive brightest points can be used to determine the star's luminosity, or brightness compared to the Sun.Mar 27, 2015.
In the example above the Cepheid has a mean apparent magnitude of 15
,56 and a period of 4,76 daysKnowing the period of the Cepheid we can now determine its mean absolute magnitude, M, by interpolating on the period-luminosity plot
The one shown below is based on Cepheids within the Milky Way
This value was based on the results of the Cepheid studies which were then combined with other techniques such as observations of Type Ia supernovae, Type II supernovae, the Tully-Fisher relation and the surface brightness of galaxies
The uncertainty of the value was close to the original +/- 10% target for the project
Named after delta-Cephei, Cepheid Variables are the most important type of variable because it has been discovered that their periods of variability are related to their absolute luminosity
This makes them invaluable as a contributer to astronomical distance measurement
The periods are very regular and range from 1 to 100 days
Type of variable star
Beta Cephei variables
Also known as Beta Canis Majoris stars
Are variable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces
Thought due to the unusual properties of iron at temperatures of 200
000 K in their interiors.These stars are usually hot blue-white stars of spectral class B and should not be confused with Cepheid variables
Which are named after Delta Cephei and are luminous supergiant stars.
Type of variable star that pulsates radially
A Cepheid variable is a type of variable star that pulsates radially
Varying in both diameter and temperature.It changes in brightness
With a well-defined stable period and amplitude.
Classical Cepheids are a type of Cepheid variable star.They are young
Population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude up to about 2 magnitudes.Classical Cepheids are also known as Population I Cepheids
Type I CepheidsAnd Delta Cepheid variables.
Type of star that is luminous, blue, and variable in brightness
Luminous blue variables (LBVs) are massive evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness.They are also known as S Doradus variables after S Doradus
One of the brightest stars of the Large Magellanic Cloud.They are extraordinarily rare
With just 20 objects listed in the General Catalogue of Variable Stars as SDor
And a number of these are no longer considered LBVs.
Type of variable star
RR Lyrae variables are periodic variable stars
Commonly found in globular clusters.They are used as standard candles to measure (extra) galactic distances
Assisting with the cosmic distance ladder.This class is named after the prototype and brightest example
Class of luminous variable star
RV Tauri variables are luminous variable stars that have distinctive light variations with alternating deep and shallow minima.
Type II Cepheids are variable stars which pulsate with periods typically between 1 and 50 days.They are population II stars:
Star whose brightness fluctuates, as seen from Earth
