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Topic: Cepheid variable


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  Cepheid variable - Wikipedia, the free encyclopedia
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.
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 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.
en.wikipedia.org /wiki/Cepheid_variable   (605 words)

  
 Variable star - Wikipedia, the free encyclopedia
By 1786 twelve variable stars were known, among them the first eclipsing variable, Algol, discovered by Geminiano Montanari in 1669; John Goodricke in 1784 gave the correct explanation of its variability.
Variable stars are generally analysed using photometry and photospectrometry.
For regular variables, the period of variation and its amplitude can be very well established; for many variable stars, though, these quantities may vary slowly over time, or even from one period to the next.
en.wikipedia.org /wiki/Variable_star   (3578 words)

  
 The Astrophysics Spectator: Cepheid Variable Stars
Cepheid variable stars are stars that periodically pulsate because of an instability in their internal structure.
The sources of instability in a Cepheid variable are the regions where helium and hydrogen become ionized, with the region of helium becoming fully ionized the dominant instability region.
Cepheid variables subdivide into two classes: the classical Cepheid variables, which are population I stars—stars with a high metallicity, and, therefore, of the current generation of stars—and the W Virginis variables, which are population II— stars of a low metallicity stars, and, therefore, early generation stars.
www.astrophysicsspectator.com /topics/overview/DistanceCepheids.html   (648 words)

  
 Cepheid Variable Stars   (Site not responding. Last check: 2007-11-06)
The namesake star in the very important class of stars known as Cepheid variables, this star formed part of the original study in which Henrietta Leavitt first discovered that the periods of luminosity were related to their absolute luminosity.
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.
Cepheid variables can be seen and measured out to a distance of about 20 million light years, compared to a maximum distance of about 65 light years for parallax measurements.
hyperphysics.phy-astr.gsu.edu /hbase/astro/cepheid.html   (188 words)

  
 AllRefer.com - Cepheid variable (Astronomy, General) - Encyclopedia
These stars are important because the period of a Cepheid depends on its intrinsic brightness, or absolute magnitude, in a known way: the brighter the star, the longer its period.
All Cepheid variables with the same period have nearly the same intrinsic brightness, but their apparent brightnesses differ because they are at different distances.
Cepheids are yellow supergiant stars, and their fluctuations in luminosity result from an actual physical pulsation, with attendant changes in surface temperature and size.
reference.allrefer.com /encyclopedia/C/Cepheidv.html   (457 words)

  
 Cepheid variable: Facts and details from Encyclopedia Topic   (Site not responding. Last check: 2007-11-06)
A Cepheid variable is a member of a particular class of variable star[Follow this hyperlink for a summary of this subject]s, EHandler: no quick summary.
A w virginis variable is a variable star similar to a cepheid variable....
Fomalhaut (α psa / α piscis austrini / alpha piscis austrini) is the brightest star in the constellation piscis austrinus and one of the brightest...
www.absoluteastronomy.com /encyclopedia/c/ce/cepheid_variable.htm   (1050 words)

  
 Cepheid variable
A yellow giant or supergiant pulsating variable whose period of pulsation is directly related to its luminosity: the longer the period, the greater the mean intrinsic brightness.
This strict period-luminosity relationship makes Cepheids important cosmic distance indicators, since, by measuring a Cepheid’s period and comparing the intrinsic brightness, which this yields, with the apparent brightness, the star’s distance can be worked out.
The light curves of Cepheid variables have a characteristic shark-fin shape, with a rapid rise to maximum, a brief stay at peak brightness, and a smooth, slow decline to minimum.
www.daviddarling.info /encyclopedia/C/Cepheid_variable.html   (309 words)

  
 Cepheid variable: Encyclopedia topic   (Site not responding. Last check: 2007-11-06)
A Cepheid variable is a member of a particular class of variable star (variable star: A star that varies noticeably in brightness) s, notable for a fairly tight correlation between their period of variability and absolute stellar luminosity.
A three-day period Cepheid has a luminosity of about 800 times the Sun (Sun: A typical star that is the source of light and heat for the planets in the solar system).
Some Cepheid stars (for example Polaris (Polaris: The brightest star in Ursa Minor; at the end of the handle of the little dipper; the northern axis of the earth points toward it)), have shown a decrease in their oscillation over a period of few tens of years, and now are virtually constant.
www.absoluteastronomy.com /reference/cepheid_variable   (567 words)

  
 Stellar Evolution - Variable Stars
Variable stars are named after a prototype star that exhibits a particular pulsation period.
Using the distance modulus, it is possible to use the Cepheid variable as a ruler for interstellar measurements.
Cepheid rulers have been used for nearby galaxies, but Type 1a supernova are better for intergalactic distances.
astronomyonline.org /Stars/VariableStars.asp   (311 words)

  
 ASP: A Taste of Real Astronomy — The ESA/ESO Astronomy Exercises
The small variations in distance to the individual Cepheid variable stars in the Cloud are negligible compared with the much larger distance to the SMC.
In this way Cepheid variable stars can be used as one of the 'standard candles' in the Universe that act either as distance indicators themselves or can be used to calibrate (or set the zero point for) other distance indicators.
Cepheid variables can be distinguished from other variable stars by their characteristic light curves (see Fig.
www.astrosociety.org /education/publications/tnl/57/realastro3.html   (1099 words)

  
 The Astronomical Distance Scale   (Site not responding. Last check: 2007-11-06)
Variable stars have proven to be one of the most reliable types of "standard candles".
Cepheid Variables are giant stars which have instabilities in their envelopes that cause them to pulsate in size, temperature and luminosity over timescales of a few days.
With HST Cepheids are being studied in galaxies in the Virgo Cluster.
cassfos02.ucsd.edu /public/tutorial/Distances.html   (919 words)

  
 Cepheid variable - Hutchinson encyclopedia article about Cepheid variable   (Site not responding. Last check: 2007-11-06)
The time that a Cepheid variable takes to pulsate is directly related to its average brightness; the longer the pulsation period, the brighter the star.
This relationship, the period luminosity law (discovered by US astronomer Henrietta Leavitt), allows astronomers to use Cepheid variables as ‘standard candles’ to measure distances within our Galaxy and to nearby galaxies.
They are named after their prototype, Delta Cephei, whose light variations were observed in 1784 by English astronomer John Goodricke.
encyclopedia.farlex.com /Cepheid%20variable   (155 words)

  
 AAVSO: Delta Cep, September 2000 Variable Star Of The Month
Cepheid variable stars, named for their archetype delta Cephei, have provided astronomers with a wealth of information about our Universe, a feat that no other class can claim.
As a class, Cepheid variable stars are characterized by a change in brightness of several hundredths to 2 magnitudes, which occurs with extreme regular periodicity of just 1 to 135 days.
The light curves of W Vir variables for some intervals of periods differ from the light curves of delta Cep variables for corresponding periods either by amplidtues or by the presence of humps on the descending branch, sometimes turning into broad flat maxima.
www.aavso.org /vstar/vsots/0900.shtml   (3768 words)

  
 Roller Coaster Stars - Astronomy In Your Hands
For a variable star this is the time between it reaching a peak of brightness, and reaching its next peak of brightness.
Cepheids are stars at a particular stage in their life cycles.
Cepheids typically change brightness by between half and two magnitudes, and have periods of between 1 and 50 days.
www.astronomyinyourhands.com /activities/rollercoaster.html   (1578 words)

  
 AAVSO: X Cygni, September 2002 Variable Star Of The Month
Turner (1998) states that the majority of Cepheids with a positive change in period are in the 3rd crossing of the instability strip, as is thought to be the case with X Cyg.
Once the variable is pinpointed, observers should then use the AAVSO 'aa' scale chart to make brightness estimates of the star as it varies through its cycle.
Cepheids are an exciting class of star to ponder over, as they are an important in the study of stellar evolution and the in the distance determination of the universe.
www.aavso.org /vstar/vsots/0902.shtml   (2140 words)

  
 RR Lyrae variable - Wikipedia, the free encyclopedia
RR Lyrae variables are variable stars often used as standard candles.
They pulse in a manner similar to Cepheid variables, but some important differences exist.
This type of variable is named after the prototype, the variable RR in the Lyra constellation.
en.wikipedia.org /wiki/RR_Lyrae_variable   (268 words)

  
 HubbleSite - Cepheid Variable Star in Galaxy M100 - Image - 10/26/1994
Typically, Cepheids in a crowded region of a distant galaxy are too faint and the resolution too poor, as seen from ground-based telescopes, to be detected clearly.
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.
Astronomical images may vary in size and resolution for several reasons: different cameras have detectors of different pixel size, images may be cropped from larger fields, and the images may consist of mosaics of several images.
hubblesite.org /newscenter/newsdesk/archive/releases/1994/49/image/a   (565 words)

  
 Cepheid Variables - Introduction
Cepheid stars oscillate between two states: In one of the states, the star is compact and large temperature and pressure gradients build up in the star.
Cepheid variable stars have masses between five and twenty times the mass of our Sun.
Because these envelopes are more extended and the density in their envelopes is lower, their variability period, which is proportional to the inverse square root of the density in the layer, is longer.
imagine.gsfc.nasa.gov /docs/science/mysteries_l1/cepheid.html   (695 words)

  
 Iowa Robotic Telescope Facilities
Goodricke had correctly deduced that the regular variation of Algol was due to the star being in a binary system, and that the companion occulted the light from Algol once per orbit.
The variability is caused by pulsation in the size and temperature of the star.
Cepheid variables are also giants but their periods are in the range of days to weeks.
phobos.physics.uiowa.edu /curriculum/intbin.html   (704 words)

  
 Interstellar Medium and the Milky Way
Leavitt found a very useful relationship for a certain type of variable star called a Cepheid variable (after the prototype in the constellation Cepheus; see stage 6 of a star's life cycle).
The fainter Cepheids in the Magellanic Clouds have shorter periods.
Type II: W Virginis Cepheids are from older low-metallicity stars and are about 4 times less luminous than Type I. Below is the light curve of a W Virginis Cepheid from the Hipparcos database of variable stars.
www.astronomynotes.com /ismnotes/s5.htm   (1165 words)

  
 H_0 and Cepheid Variables; Astro 228, Fall 2002
Cepheid variable stars have proven to be some of the most useful distance indicators currently available.
Cepheids are what much of the cosmological distance scale is bootstrapped to and a more precise measurement of cepheid distances means a more precise measurement of the local value of the Hubble constant, H
Cepheids as a rung on the distance ladder.
www.josephhall.org /ho   (436 words)

  
 Cepheid Variable Stars & Distance
Eventually she classified 47 of these in the two clouds as Cepheid variables and noticed that those with longer periods were brighter than the shorter-period ones.
By measuring the period of a Cepheid from its light curve, the distance to that Cepheid could be determined.
He also studied Cepheids in 86 globular clusters and found that the few dozen brightest non-variable stars in each cluster was about 10 × brighter than the average Cepheid.
outreach.atnf.csiro.au /education/senior/astrophysics/variable_cepheids.html   (1384 words)

  
 Curious About Astronomy: What is a Cepheid variable?   (Site not responding. Last check: 2007-11-06)
Cepheid variables are a subgroup of a class of stars called variable stars.
Cepheid variable stars have masses between five and twenty times the mass of the sun.
It was the observations of Cepheid variable stars which enabled astronomer Hubble (after whom the Hubble Space Telescope is named) to determine that spiral nebulae like the one in Andromeda were galaxies separate from the Milky Way.
curious.astro.cornell.edu /question.php?number=33   (263 words)

  
 Main Page - Cepheidopedia
A type of variable star which exhibits a regular pattern of changing brightness as a function of time.
This is a collaborative effort to compile Cepheid data and lore into the written tradition, instead of the oral tradition mostly used up until now.
A problem faced by knowledge compilers in the past was how apathetic Cepheids are in general, and the rapidity with which data grew stale.
www.cepheid.org /wiki/index.php/Main_Page   (276 words)

  
 Polaris   (Site not responding. Last check: 2007-11-06)
If we can measure how long it takes a cepheid in another galaxy to vary its brightness we can learn how intrinsically bright it is. Once we know that we can tell how far away the galaxy must be in order for that star to look as faint as it does from the Earth.
For most cepheids, at any given time, all the material making up the star is moving in the same direction; this type of pulsation is called fundamental mode pulsation and is shown in Figure 1a.
At a particular depth in the atmosphere there is a boundary, called a node, inside of which all the gas is moving in one direction while outside the node all the gas is moving in the opposite direction.
ftp.nofs.navy.mil /projects/npoi/science/cepheids.htm   (1129 words)

  
 Variable Stars   (Site not responding. Last check: 2007-11-06)
Her work at the Harvard College Observatory early in this century was instrumental in the cataloguing of variable stars and in the realization that Cepheid variables could be used to establish a distance scale (Ref).
The following figure shows the variation in brightness, temperature, spectral class, surface velocity, and radius for the prototype Cepheid variable, delta-Cephei, as a function of the phase of the pulsation period, as does this animation.
By making careful brightness measurements of Cepheid variable stars detected in this galaxy, it was possible to determine that it lies at a distance of 19.1 parsecs (about 60 million light years) (Ref).
csep10.phys.utk.edu /astr162/lect/variables/variables.html   (174 words)

  
 Non-pulsating Cepheid Variables
As the arrival time "clock" varies in speed, the stellar spectrum changes in color (Hottest at peak, coolest at trough.) Here, we are considering a bright star with a dim (mostly unseen) companion.
In the Cepheid variable studies I have seen, Case 2 slow rise-fast decay (SRFD), light curves are extremely rare, less than one percent and those published are very close to being symmetrical.
Cepheid variables with greater FRSD effects may tend to be located in regions of space with greater extinction lengths.
www.datasync.com /~rsf1/cepheids.htm   (677 words)

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