IK Pegasi

IK Pegasi (also called and) is a binary star of the Constellation of PEGASE. Located at a distance from 150 light-years of the Solar system, it is just enough luminous to be visible with the naked eye, its magnitude apparent being of 6,078.

The primary star (IK Pegasi A) is a star of the principal Séquence of standard spectral has. It is a variable star of standard Delta Scuti: its luminosity undergoes a light periodic variation 22,9 times per day.

Observation

The stellar Système is referred in the Bonner Durchmusterung (catalogs astrometrical of Bonn) of 1862 and the Harvard Revised Photometry Catalog Pickering of 1908 under respective designations BD +18°4794B and HR 8210. The name IK Pegasi follows the nomenclature of variable stars introduced by Friedrich W. Argelander.

The spectrum of this star is marked by a shift of the absorption lines by Doppler effect characteristic of the binary systems SB1. The rotation of two stars around the center of gravity of the system generates a movement of stars along the line of sight which causes this shift. Its measurement makes it possible to the astronomers to calculate the radial speed of principal although they are unable to solve the two components.

In 1927, the Canadian astronone William E. To grip obtains by this method the period and the Excentricité of this Binaire to a spectrum which are respectively 21,724 days and 0,027.

The distance between IK Pegasi and the Sun were given by using the Parallaxe system during the annual movement of the Earth around the Sun. This shift was evaluated with precision by the telescope Hipparcos. The distance from star was estimated at 150 light-years (± 5 light-years). The satellite also measured the own Mouvement system.

The transverse speed of IK Pegasi is calculated using the values of the distance and the own movement of the system: it is of 16,9 km/s. the radial Speed of the system is obtained by measuring the shift of its spectrum by Doppler effect: this speed is of -11,4 km/s according to the General Catalog off Radial Stellar Velocities ( catalogs general stellar radial speeds ). The addition of these two movements gives a space speed of 20,4 km/s compared to the Sun.

An attempt was carried out to photograph the two components of binary star using the Space telescope Hubble. This one failed because the two stars were too close for the to solve. Recent measurements with the Extreme Ultra-violet To explore made it possible more precisely to consider the period orbital at 21,72168 ± 0,00009 days. The slope of the orbital plane of the system would be close to 90° sight of the Earth: if it is indeed the case, it would be possible to observe an eclipse.

The pulsations are due to a process called the mechanism κ . Part of the external atmosphere of star becomes opaque because of the Ionization partial of some elements. When these Atome S loses a electron, the Probabilité that they absorb of the energy increases. This phenomenon generates an increase in the Température which is responsible for the expansion of the atmosphere. The ionization of the dilated atmosphere decreases and this one loses energy, cools and contracts. The atmosphere thus undergoes a periodic cycle of expansion-contraction which is at the origin of the periodic pulsations of its luminosity.]] The stars of the part of the band of instability which crosses the principal Séquence are called variable of type Delta Scuti in reference to Delta Scuti. The variable of type Delta Scuti generally go from the spectral classes A2 in F8 and from the classes of luminosity MKK III (Under-giantess) with V (star of the principal sequence). They are variables at weak period, between 0.025 and 0.25 days. The chemical abundance of the variables of the type Delta Scuti is close to that to the Sun and their mass ranging between 1,5 and 2,5 solar Masses. The frequency of the pulsations of IK Pegasi has is of 22,9 per day, that is to say every 0,044 days. The spectrum of IK Pegasi has is classified like marginal Am (or Am:) : it has the spectral characteristics of the class has but with more marked metal lines. The atmosphere of star has slightly more (abnormally) of force of the absorption lines for the metal Isotope S

The stars of class has are hotter and more massive than the Sun, they remain less longer on the principal sequence. A star of the mass of IK Pegasi has (1,65 mass solar) there passes approximately 2 - years, that is to say half of the age of the Sun.

In term of mass, the star similar to the component With nearest to the Sun is Altair. Its mass is estimated at 1,7 solar mass. The binary system presents some resemblances to Sirius which is composed of a star of class has and of dwarf white. Sirius has is however more massive than IK Pegasi has and the orbit of his/her companion, whose equatorial radius is of 20 U.A., is further away from the center of gravity of the system.

Component B

The component B is a white Naine. These extinct stars is not any more the theater of reactions fusion nuclear. In the majority of the cases, these stars cool gradually during several billion years.

Evolution

Almost all the stars of low or intermediate mass (lower than nine solar masses) become the dwarf white ones after having exhausted their fuel reserves, among which the Hydrogène, the Hélium and other elements. These stars pass most of their life in the principal sequence. The duration during which a star remains on this zone of diagram HR depends mainly on its mass: the higher this one is, the more this duration is weak. Thus, IK Pegasi B was to have a mass more raised than IK Pegasi has because it became dwarf white before her companion. A study of 1993 estimates that the mass of its progénitrice would have lain between five and eight solar masses.

The ray of the red giants and the stars AGB can reach several hundreds of times the solar ray by dilation of the external envelope. For example, pulsating star AGB has a ray of approximately (3 UA). These values are quite higher than the distance separating two stars from IK Pegasi: during this period, the two stars had a common envelope. Consequently, the atmosphere of IK Pegasi has could have been contaminated by his/her companion, thus modifying his composition Isotopique. The ejected materials formed an immense cloud called Nébuleuse planet gear. The hydrogen envelope is almost completely ejected star, leaving only one dwarf white formed mainly of the inert heart.

Composition and structure

The core of IK Pegasi B could be made up either of carbon and oxygen, or of neon and oxygen if the reaction of combustion of carbon occurred in within its star progénitrice. In this last case, its coat would be rich in carbon and oxygen. In the two scenarios, the external layer of star is made up almost exclusively hydrogen: IK Pegasi B is thus a star of class DA. Because of its Atomic mass more raised, the helium of the envelope will have migrated under the layer of hydrogen. Although IK Pegasi B could not be observed directly, its ray can be estimated using the theoretical relation connecting the mass and the ray of dwarf white. The ray of IK Pegasi B is of approximately 0,60 %.

Being given its mass and its density, the gravity of surface of dwarf white is high. The astronomers note it using the decimal logarithm of the acceleration of the gravity expressed in the system of units CGS and noted log G . The value of log G is equal to 8,95 for IK Pegasi B. In the absence of companion, the dwarf white one would continue to cool during more than one billion years while its ray would remain roughly constant.

Future trend of the system

In an article of 1993, David Wonnacott, Barry J. Kellett and David J. Stickland estimate that the system could evolve/move in supernova of the cataclysmic Ia type or variable.

At a certain point, the hydrogen integrality of the core of IK Pegasus has will have burned. The star will leave the principal sequence and will become a red giantess. The ray of star significantly will increase and can reach more than one hundred times the initial ray of star. As from the moment when the external envelope of IK Pegasi has will exceed the Lobe of Rock of his/her companion and a Disque of accretion gas will be formed around dwarf white. This gas, made up mainly hydrogen and of helium, will accumulate on the surface of his/her companion. This mass transfer between two stars will involve a reduction in the distance between two stars.

On the surface of dwarf white, the accretion gas is compressed and its temperature increases. When the pressure and temperature of the layer of hydrogen become enough large to start a nuclear reaction of Fusion, a great quantity of hydrogen is transformed into helium and others heavier elements. The enormous quantity of energy released by this process expels remaining gases of the surface of dwarf white and produces a extremely luminous glare but of short duration: the luminosity of dwarf white will increase by several magnitudes during a few days or month. RS Ophiuchi is an example of binary star star consisted of a red giantess and a companion dwarf white. RS Ophiuchi knew at least six eruptions since 1898.

It is possible that IK Pegasi B evolves/moves in this manner.

Another model in which the dwarf white one accumulates matter without becoming a nova is that of the source of x-rays of very low energy resulting from a tight binary system ( closed-binary supersoft X-ray source (CBSS) ). In this scenario, the mass rate of transfer to the dwarf white one is such as a reaction of fusion proceeds continuously on the surface. Arriving hydrogen is transformed into helium by the reaction. These sources are the dwarf white ones of strong mass with temperatures of very high surfaces (0.5– 1 × 10⁶ K).

When dwarf a white approach the Limit of Chandrasekhar of 1,44 solar masses, the pressure of radiation is not sufficient any more to be opposed to gravity and the star crumbles. When the core is made up mainly of oxygen, neon and magnesium, the formed star is in the majority of the cases a neutron star. In this case, only part of the mass of star is then ejected. If on the contrary the core is composed of carbon and oxygen, a substantial fraction of star returns in nuclear fusion during a short amount of time following collapse. The star explodes then in the form of a supernova of the Ia type.

The possible explosion of IK Pegasi B would not be a threat for the terrestrial Vie. Indeed, it is not very probable that IK Pegasi has becomes in a near future a red giantess. Moreover, it moves away from the Sun at a speed of 20,4 km/s, is one light-year all them: 14700 years. In 5 million years, this star should be located at more 500 light-years of the Earth, that is to say more than the ray of the sphere within which a supernova of the Ia type would be dangerous. The explosion of the supernova will create a remanent ejected matter which will spread in the interstellar Milieu.

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