Polaris pulsates with 3.97 day period. The luminosity varies by 0.15 magnitude. Polaris is classified as a Population II Cepheid. Stars of this type are about 1.5 magnitudes smaller than Population I Cepheids.
The Distance Scale in the Universe ...
Why Do Stars Pulsate?
We tend to think of stars as stable and unchanging. As we shall see in the next section on stellar evolution however, stars undergo several stages in their existence.
Variable stars that pulsate have what are called "normal modes" of oscillation. These normal modes can be 3D-symmetric, "radial" modes where the star expands and contracts with the frequency of the mode.
They pulsate with periods < 1 day. Cepheids pulsate with periods > 1 day. The longer the pulsation, the more luminous they are. There are two types of Cepheids: classical (brighter, type I) and W Virginis (fainter, type II).
Variable stars are stars whose luminosity varies with time as the star pulsates. In particular there is a class of variable star known as Cepheid Variables. The stars vary by about one magnitude over periods ranging from one to 100 days.
Such stars, all class F, G, and K bright giants and supergiants, are in a critical "zone" of temperature and luminosity that makes them unstable and to pulsate.
(a) A yellow supergiant that pulsates, alternately brightening and dimming. Cepheids allow astronomers to measure distances, because the longer a Cepheid's period of variation, the greater the Cepheid's mean intrinsic brightness.
Why do Cepheids and RR Lyrae variables pulsate? The basic mechanism was first suggested by the British astrophysicist Sir Arthur Eddington in 1941.
Cepheid variable stars are stars that periodically pulsate because of an instability in their internal structure. They grow brighter and dimmer on a regular cycle as they pulsate radially, alternately become physically larger and then smaller.
For example, they use a class of variable known as Cepheids, which pulsate in and out like beating hearts. There is a direct relationship between the length of a Cepheid's pulsation and its true brightness.
If you remember from the previous section, Cepheids are those Red Giant stars that pulsate and you can use them to determine distance.
Cataclysmic variables always have a binary companion, and do not pulsate via the same mechanism as the other variable stars so-far discussed. They draw matter from their companion star, as shown in the diagram above.
In 1907, Henrietta Leavitt discovered that Cepheid variable stars in the Small Magellanic Cloud pulsated at a rate which depended solely on their absolute magnitude.
This interaction can heat the gas being exchanged between the bodies and produce X-ray light which can appear to pulsate, causing binary pulsars to occasionally be referred to as X-ray binaries.
Like all Beta Cephei stars, however, Alfirk pulsates with many periods at once, smaller changes taking place with a variety of other periods between four and five hours, in addition to 6- and 12-day rotational modulations.
All through the galaxy, we find stars that pulsate. Gravity makes stars spherically symmetric. Because of this symmetry, we can describe the pulsations with mathematical functions called spherical harmonics.
Cepheid variables are supergiant stars that regularly pulsate in size and change in brightness. As the star increases in size, its brightness decreases; then, the reverse occurs. The luminosity is proportional to the period.
Delta Scuti variables are fairly young stars which pulsate, creating a slight variation in visual magnitude, less than 0.5 magnitude and often considerably less than this, with a short period (from 30 minutes to about eight hours).
As a result it cools and expands, allowing dust to form in its outer envelope, and begins to pulsate. This in turn expels the dust into the surrounding area at speeds of up to 30,000 miles per hour.
Cepheid Variable
This is a variable star whose light pulsates in a regular cycle. The period of fluctuation is linked to the brightness of the star. Brighter Cepheids will have a longer period.
Chaos
A distinctive area of broken terrain.
The pulsating variables expand and contract cyclically, causing them to pulsate rhythmically in brightness and size. The Cepheids and RR Lyrae stars are typical examples of such variables.
Various groups of red giant stars that pulsate with periods in the range of weeks to several years. The period is not always constant but changes from cycle to cycle. Mira variables ...
intrinsic variable: A variable star driven to pulsate by processes in its interior.
inverse square law: The rule that the strength of an effect (such as gravity) decreases in proportion as the distance squared increases.
These stars pulsate because the hydrogen and helium ionization zones are close to the surface of the star. This more or less fixes the temperature of the variable star, and produces an instability strip in the H-R diagram.
In fact, it would have been extremely difficult to detect this substellar object around a highly evolved star like Edasich, because giant stars often pulsate and produce radial velocity patterns similar to substellar companions.
It changes brightness as it pulsates due to upward traveling shock waves, with a long period due to its large distended size of the star, which is an M6 . However, the spectral type changed from M8 at minimum brightness to M2 at maximum brightness.
Since the hydrogen-burning shell and helium-burning core do not produce energy in a stable and steady manner, the star will pulsate and generate strong stellar wind. Eventually, the entire outer shell will be ejected.
LONG-PERIOD VARIABLE - A highly evolved, very luminous red giant star whose atmosphere expands and contracts in repeating cycles (i.e., it pulsates) with periods from several months to several years.
Stunning auroras pulsated even at near tropical latitudes over Cuba, the Bahamas, Jamaica, El Salvador, and Hawaii. Spark discharges shocked telegraph operators and set the telegraph paper on fire.
to spot without specialized equipment; the stars are a distinctly deep red or brown colour described as "smoky". All carbon stars are variable stars, with irregular or semiregular variables; that is, they vary in brightness and appear to pulsate, ...
A source that pulsates in the radio or x-ray spectrum is called a "pulsar" and it is generally believed that a pulsar is a neutron star (although some of the pulsars with longer periods might be white dwarfs).
 See also: Star, Sun, Period, Light, Earth
  
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