IK Pegasi

from Wikipedia, the free encyclopedia
Double star
IK Pegasi
Location of IK Pegasi.png
The position of IK Pegasi
Observation
dates equinox :  J2000.0 , epoch : J2000.0
AladinLite
Constellation Pegasus
Right ascension 21 h 26 m 26.7 s
declination + 19 ° 22 ′ 32.3 ″
Apparent brightness  6.08 mag
Astrometry
Radial velocity −11.4 km / s
parallax 21.72 ± 0.78 mas
distance  150 ± 5 ly
(46 ± 2 pc )
Proper movement :
Rec. Share: +80.23 mas / a
Dec. portion: +17.28 mas / a
orbit 
period 21.7 days
Individual data
Names A; B.
Observation data:
Apparent brightness A. 6.08 mag
B.
Typing:
Spectral class A. A8m:
B. THERE
B − V color index A. 0.24
U − B color index A. 0.03
Physical Properties:
Absolute vis.
Brightness M vis 		A. approx. 2.8 mag
B.
Dimensions A. 1.65 M ☉
B. 1.15 M ☉
radius A. 1.6 R ☉
B. 0.006 R ☉
Luminosity A. 8.0 L ☉
B. 0.12 L ☉
Effective temperature A. 7700 K
B. 35,500 K
Metallicity [Fe / H] A. 0.17 ± 0.17
B.
Rotation time A. <32.5 km / s d
B.
Age 50–600 million years
Other names
and catalog entries
Bonn survey BD + 18 ° 4794
Bright Star Catalog HR 8210 [1]
Henry Draper Catalog HD 204188 [2]
SAO catalog SAO 107138 [3]
Tycho catalog TYC 1671-710-1 [4]
Hipparcos catalog HIP 105860 [5]
Further designations: IK Pegasi
  WD 2124 + 191 • EUVE J2126 + 193
Swell:

IK Pegasi ( HR 8210 ) is a double star in the constellation Pegasus, about 150  light years away . The two stars cannot be resolved as individual objects, rather it is a spectroscopic double star , which means that they can only be identified as a double star by their spectrum . With an apparent brightness of 6.1 mag, the object can barely be seen with the naked eye under very good observation conditions.

The primary star (IK Pegasi A) is a main sequence star of the spectral class A, which shows a slight pulsation in its luminosity , which is repeated 22.9 times per day. These pulsations are primarily generated by instabilities in the hydrogen convection zone, which alternately lead to the expansion and contraction of the atmosphere. Among the pulsation variables , IK Pegasi A belongs to the Delta Scuti stars .

Its companion (IK Pegasi B) is a white dwarf and thus a star that has already had the majority of its development phase and is now no longer able to generate energy through nuclear fusion . Both orbit each other every 21.7 days at an average distance of about 31 million kilometers or 0.21  astronomical units (AU). This distance roughly corresponds to the distance between Mercury and our sun .

IK Pegasi B is the known closest to us candidate for a supernova of type Ia . Such an event occurs when the main star begins to reach the developmental stage of a red giant . Its radius grows so much that the neighboring white dwarf accretes matter from its expanding gaseous shell . As soon as the white dwarf approaches the Chandrasekhar limit of 1.44  solar masses , it is expected to explode as a Type Ia supernova.

Observation history

The star system was first cataloged in the star catalog Bonner Durchmusterung published in 1862 under the entry BD + 18 ° 4794 B. It was later mentioned in Pickering's 1908 Bright Star catalog under the designation HR 8210 . The name "IK Pegasi" is based on the extended form of naming variable stars , which was introduced by Friedrich W. Argelander .

Investigations of the spectrometric properties of this star revealed characteristic shifts of the absorption lines that clearly indicate a binary star system. Such a shift occurs when the two partners move towards or away from the observer during their mutual rotation, as a result of which a periodic Doppler shift occurs within the wavelength of the spectral lines. The measurement of this displacement in turn allows the astronomers to determine the relative orbital velocity of at least one of the stars without the objects being able to be resolved individually.

In 1927, the Canadian astronomer William E. Harper used this technique to measure the period of the spectrometric shift of this binary system, finding an interval of 27.724 days between the two phases. He also estimated the eccentricity of the orbit to be 0.027; later estimates showed an eccentricity of practically zero, which is equivalent to a circular orbit. The maximum deflection of the radial speed of the main star was determined to be 41.5 km / s.

The distance from IK Pegasi to the earth can still be determined by a parallax measurement. The displacement was ultimately measured with high precision by the Hipparcos probe and the distance to this double star was determined to be 150  light years with an accuracy of ± 5 light years. This space probe was also used to determine the system's own movement , i.e. the small angular movement that IK Pegasi makes during its movement across the sky, while it moves through space.

The combination of distance and movement of the system could in turn be used to determine a lateral speed of IK Pegasi of 16.9 km / s. The third component, the heliocentric radial velocity, can be determined from the average redshift (or blueshift) of the stars' spectrum. In the General Catalog of Stellar Radial Velocities (General Catalog of the Radial Velocities of Stars) a radial velocity of −11.4 km / s is given for this system. From these two movements, a space velocity can in turn be derived, which corresponds to a value relative to the sun of 20.4 km / s.

Attempts have already been made to resolve the individual components of this binary system with the help of photographs from the Hubble Space Telescope , but the distance between the two stars has proven to be too small for them to be identified separately. With the Extreme Ultraviolet Explorer (EUVE) space telescope , current measurements have now been carried out, so that a more precise orbital time of 21.72168 ± 0.00009 days could now be determined for the double stars. The orbital inclination of the orbital plane of this system when the object is observed from Earth appears to be close to 90 °. Under these circumstances it would be possible to observe the larger object being covered by the smaller white dwarf, which would be noticeable through a noticeable decrease in brightness.

IK Pegasi A

In its current state, IK Pegasi A is a star that is included in the main sequence within the Hertzsprung-Russell diagram (HR diagram) . The term main sequence summarizes stars that release their radiation energy by burning hydrogen in their core . However, IK Pegasi A lies in a narrow, almost vertical band of the HR diagram known as the instability strip . Stars in this band oscillate in a coherent manner so that they have a regular fluctuation in their brightness.

The pulsations result from a process known as the κ mechanism . Part of the outer atmosphere of these stars appears optically dense , which is triggered by a partial ionization of certain elements. If these atoms lose an electron due to the pressure and temperature conditions within the atmospheric layer , the probability increases that energy will be absorbed by them. This causes the temperature to rise, which in turn causes the atmosphere to expand. The inflated atmosphere becomes less ionized and loses energy, causing it to cool down and shrink again. The result of these cycles is a regular pulsation of the atmosphere, which brings about a corresponding variation in brightness. Such pulsation-variable stars, which are located in the HR diagram in the vicinity of the intersection of the main sequence and instability stripes, are referred to as delta-scuti stars . They are stars with a short-cycle change in luminosity and a regular pulse rate between 0.025 and 0.25 days. In their structure, they have the same frequency of heavy elements as the sun (see Population I ), but have 1.5 to 2.5 times the solar mass . In astronomy, the metallicity of a star is defined as the frequency of the chemical elements in it , which have a higher atomic weight than helium. This frequency is determined by means of a spectral analysis of the atmosphere, the result of which is then compared with the results that one would expect according to the results calculated by computer models. In the case of IK Pegasus A, the solar metallicity is estimated to be [M / H] = 0.07 ± 0.20. This value describes the logarithm of the ratio between metals (M) to hydrogen (H), minus the logarithm of the corresponding ratio of our sun. (If a star had exactly the metallicity of the sun, its metallicity value would be zero.) A logarithmic value of 0.07 corresponds to an actual metallicity ratio of 1.17, which means that the star is over 17% richer in metallic elements is as our sun. However, the margin of error for this result is relatively large. The pulse rate of IK Pegasi A was measured at 22.9 cycles per day, which corresponds exactly to one radiation pulse every 0.044 days.

In the spectrum of an A-class star like IK Pegasi A, strong Balmer lines of hydrogen can also be seen along with absorption lines of ionized metals, including a K line that points to ionized calcium (Ca II) at a wavelength of 393, 3  nm . The spectrum of IK Pegasi A can thus be classified as marginal Am, which means that on the one hand it shows the features of a spectral class A, but on the other hand it has a marginal metallic series. The reason for this is that in the atmosphere of this star, compared to normal stars, slightly different but noticeably higher absorption line strengths of the metallic isotopes can be seen. Stars of the spectral class Am are often members of binary star systems which, like IK Pegasi, have a very close companion of roughly the same mass.

Spectral class A stars are hotter and more massive than the sun. However, this in turn means that their service life on the main row is correspondingly shorter. For a star with a mass similar to that of IK Pegasi A (which has about 1.65 solar masses), the expected lifetime on the main sequence is between 2 and 3 × 10 9 years, which corresponds to about half the current age of our sun.

In terms of mass, the relatively young Altair is the closest star to the Sun, which can be cited as a stellar counterpart to the A component of IK Pegasi, as it is estimated to have 1.7 times the solar mass . Overall, the double star system of IK Pegasi has some similarities to the nearby system of Sirius , which also consists of a class A primary star and a white dwarf as a companion. However, Sirius A has a significantly larger mass than IK Pegasi A and the orbit of its companion, with a semi-axis of 20 AU, is much larger in comparison.

IK Pegasi B

The relative size of IK Pegasi A (left), B (bottom) and the sun (right)

IK Pegasi A's companion is a dense white dwarf . This category of stellar objects has already reached the evolutionary end of its life and is no longer able to sustain energy production through nuclear fusion . Under normal circumstances, it then continuously emits its excess energy, which consists primarily of stored heat, which makes it increasingly cooler and darkens more and more over the course of a few billion years.

Development so far

Almost all stars of low and medium mass (below about nine solar masses ) end up as white dwarfs as soon as their supply of fuel has been exhausted. These stars previously spent most of their energy-producing lifetimes as main sequence stars . The period of time a star spends on the main sequence depends primarily on its mass, since the life span of a star decreases with increasing mass. Since IK Pegasi B exists as a white dwarf, it can be concluded that he must once have had a larger mass than his companion. Therefore it is assumed at IK Pegasi B that it once possessed a mass between 5 and 8 solar masses.

To understand how this stage of development came about, one has to look back a few million years into the past. When the hydrogen in the core of the forerunner star of IK Pegasi B was used up, its inner core contracted until hydrogen burned again in a shell around its helium core, which led to a temperature increase inside the star. To compensate for the increase in temperature, the outer mantle expanded many times the radius of a normal main sequence star. The now greatly enlarged shell cooled down and thus formed the visible red glowing outer shell that characterizes a red giant . As soon as the core had reached a temperature and density at which the helium merged, the star contracted even further and now belonged to a group of stars that is located on a roughly horizontal line on the HR diagram. The helium fusion formed an inner core of carbon and oxygen. When the helium in the core was finally exhausted, in addition to the outer shell in which the hydrogen burned, another shell was created into which the helium burn was now shifted. The star shifted within the HR diagram in a range that the astronomers Asymptotic Giant (engl. Asymptotic giant branch, Conditions) call. If the forerunner star of IK Pegasi B had enough mass, carbon burned in its core over time , producing oxygen , neon and magnesium .

In general, the outer shell of a red giant or AGB star expands to several hundred times the solar radius (the pulsating AGB star Mira, for example, reaches a radius of about 5 × 10 8  km (3  AU ). ) which is why this can also be assumed for IK Pegasi B. The expansion of the envelope had exceeded the distance that the two stars of IK Pegasi have on average today, so that both had to share a common envelope during this time. This in turn had the consequence that in this phase the outer atmosphere of IK Pegasi A was supplied with an increased number of isotopes.

The Helix Nebula is the result of the evolution of a star into a white dwarf. (Image: NASA & ESA )

Some time after an inner oxygen-carbon or oxygen-magnesium-neon core formed, nuclear fusion occurred in two concentric shells around the core region. Hydrogen was burned on the outermost of the two shells, while the helium fusion took place around the inner core. However, such a double-shell phase is unstable, which leads to so-called thermal pulses , which result in a large amount of mass radiation from the outer envelope. This material was eventually repelled in a huge cloud of material as a planetary nebula . Except for a small part, the entire hydrogen mantle was knocked off from the star and what remained was a white dwarf, which mainly consisted of the remains of the inner core.

Composition and structure

The core of IK Pegasi B, like most white dwarfs, probably consists entirely of carbon and oxygen with a coat of hydrogen and helium. If its precursor star was capable of burning carbon , there is also the possibility that its core was composed of oxygen and neon, which is surrounded by a mantle of carbon and oxygen. Due to the higher atomic mass , any helium in the envelope must sink below the hydrogen layer, which is why one can expect that the outer envelope of IK Pegasi B is surrounded by an atmosphere of almost pure hydrogen, which means that the star can be assigned to the spectral class DA. The entire mass of the star is now only supported by the degeneracy pressure of the electrons, a quantum mechanical effect that limits the number of matter particles that can be pressed into a certain volume.

The diagram shows the theoretical radius of a white dwarf in relation to its mass. The green curve corresponds to a relativistic electron gas model.

With an estimated 1.15 solar masses, IK Pegasi B is classified as a high-mass white dwarf. Although its extent has not yet been directly observed, it is possible to estimate it based on known theoretical relationships between mass and radius of other white dwarfs. A size of 0.6% of the solar radius is assumed for him . (Other sources assume a value of 0.72%, which leaves a certain uncertainty.) In other words, this means that this star, with a mass greater than that of the Sun, is in a volume about the same size fits the earth, which gives an idea of ​​the extreme density this object possesses

The massive and compact nature of a white dwarf creates a strong surface gravity. Astronomers give this value by the decimal logarithm of gravity in CGS units, or log g . A log g of 8.95 is assumed for IK Pegasi B. In comparison, the log g for the earth is 2.99. In other words, the force of gravity on the surface of IK Pegasi is over 900,000 times the gravitational force of our earth.

The effective surface temperature of IK Pegasi B is estimated to be around 35,500 ± 1500 K, which makes this celestial body a strong source of UV radiation. Under normal conditions, such a white dwarf will continue to cool for the next more than a billion years, but its radius will remain essentially unchanged.

Development forecasts

Representation of the development of an Ia supernova

In its development of 1993 David Wonnacott, Barry J. Kellett and David J. Stickland identified this system as a candidate for the development of a supernova of type Ia or a cataclysmic variable star . At a distance of 150 light years, this system is therefore the closest known candidate for a supernova precursor. However, this variant is only one of the various scenarios that the development of such a double star can take. Basically, it can be assumed that IK Pegasi A will have used up the hydrogen in its core at a certain point and will develop away from the main sequence to a red giant . The surface of this red giant will then grow in such a way that its dimensions exceed the original radius by a hundred times or more. At some point the outer shell of IK Pegasi A has expanded so far that it exceeds the Roche limit of its companion and creates a gaseous accretion disk around the white dwarf. This gas, which is composed primarily of hydrogen and helium, increases the size of its companion. Based on observations of similar objects, it can be assumed that the two stars, triggered by the mass exchange, will steadily approach each other.

According to the most likely development prognosis , the accreted gas on the surface of the white dwarf is compressed, whereupon it is heated until the accumulated gas has the necessary conditions for hydrogen fusion at a certain point. This triggers a thermal reaction , which in turn causes part of the gas to be removed from the surface. As its mass increases, only part of the accreted gas can be shed, so with each cycle the mass of the white dwarf will continuously increase. As is usual with a recurring nova, the surface of IK Pegasus B would also grow. This creates (constant) nova explosions, which are typical for a cataclysmically variable star. During these phases, the white dwarf's brightness will increase rapidly by several magnitudes over a period of several days or months . An example of such a star system is RS Ophiuchi , a double star system, which also consists of a red giant and a white dwarf as companions. A recurrent (recurring) nova was observed at least six times at RS Ophiuchi between 1898 and 2006. Every time the white dwarf reached the critical value of its collected mass of hydrogen, another explosive thermal reaction occurred, which could then be observed as a nova.

Different binary stars, however, go through an alternative development model in which the white dwarf succeeds in steadily collecting mass without a nova event occurring. Such close binary systems are commonly known as type Super Soft X-ray source designated (super soft x-ray source, CBSS). With these objects, the transfer rate of the mass to its nearby white-dwarf companion is low enough that a continuous fusion can be maintained without the incoming hydrogen on the surface being burned in a nuclear fusion to helium. The category of Supersoft X-Ray Source includes all large white dwarfs with a very high surface temperature (0.5 × 10 6 to 1 × 10 6 K.).

Due to the steady uptake of mass, such a white dwarf will at some point approach the Chandrasekhar limit of 1.44 solar masses, above which the degenerative pressure of the electron gas can no longer compensate for the gravitational pressure and it must collapse. In the event that the core consists mainly of oxygen, neon and magnesium, this means that the collapsing white dwarf usually only blasts off a fraction of its mass and the rest eventually collapses into a neutron star . If, on the other hand, the core consists of carbon and oxygen, the increasing pressure and temperature will initiate another carbon fusion in the center before the Chandrasekhar limit is reached. The result would be an unstoppable nuclear fusion reaction that consumes a considerable part of the star's mass within a short period of time and is ultimately sufficient to tear the star apart in a massive Type Ia supernova explosion.

However, until this system has reached a state where a supernova explosion could occur, the two objects will be at a considerably greater distance from Earth, as it is extremely unlikely that the primary star, IK Pegasi A, turns into a red giant in the immediate future. For a supernova event to pose a serious threat to life on Earth, it must occur within approximately 26 light years of Earth. Only within this radius is there a possibility that the planet's biosphere could be affected and, in the worst case, the earth's ozone layer could be destroyed. The speed of this star is currently 20.4 km / s relative to the Sun, which corresponds to an increase in the distance of one light year every 14,700 years. After 5 million years, this star will be more than 500 light years away from the sun. A distance far enough outside the radius within which a Type Ia supernova would pose a threat to our solar system.

Following such a supernova explosion, the rest of the donor star (IK Pegasus A) moves at the speed it once had as a member of the binary star system. The resulting relative speed to the galactic environment can be up to 100–200 km / s, which would make this celestial body one of the fastest objects in our galaxy . The supernova explosion itself only leaves behind a residue of expanding material, which eventually goes into the surrounding interstellar matter .

literature

Web links

Commons : IK Pegasi  - album with pictures, videos and audio files

Remarks

  1. ↑ The absolute magnitude M v is calculated with:
    where V is the visual magnitude and π is the parallax.
  2. ↑ Based on:
    where L is the luminosity, R is the radius and T eff is the effective temperature.
  3. ↑ The total own movement per year is broken down into two components (μ (RA)) and (μ (Dec)); μ (RA) indicates the annual proper movement in the direction of the right ascension , μ (Dec) in the direction of declination . In this way it follows:
    .
    The resulting transverse speed is calculated from:
    .
    where d (pc) is the distance in parsecs.
  4. ↑ According to the Pythagorean theorem , the speed of the proper motion results from:
    .
    Where corresponds to the radial speed and the tangential speed.
  5. ↑ The term metals includes all elements except hydrogen and helium
  6. ↑ In this context it should be added that the members of the group of white dwarfs are closely distributed around an average value of 0.5-0.7 solar masses. Only 2% of all white dwarfs have at least the mass of our sun.
  7. ↑ The radius at 0.6% of the sun's radius gives:
  8. ↑ The gravitational force on the earth's surface is 9.78 m / s 2 or 978.0 cm / s 2 in CGS units. This results in:
    The logarithm of the gravitational difference is 8.95 - 2.99 = 5.96
    From this it follows:
  9. ↑ According to Wien's law of displacement , the peak of radiation emission from a blackbody at this temperature is at a wavelength of

    and would therefore be clearly in the ultraviolet part of the electromagnetic spectrum .

Individual evidence

  1. ↑ a b c d e f g V * IK Peg - Spectroscopic binary. In: SIMBAD. Center de Données astronomiques de Strasbourg, accessed on January 29, 2010 (English, SIMBAD database query for HD 204188. Some information can be accessed using the "Display all measurements" function on this website).
  2. ^ A b D. W. Kurtz: Metallicism and pulsation - The marginal metallic line stars . In: Astrophysical Journal . tape 221 , 1978, pp. 869-880 , doi : 10.1086 / 156090 , bibcode : 1978ApJ ... 221..869K .
  3. ↑ a b c d e f M. A. Barstow, JB Holberg, D. Koester ,: Extreme Ultraviolet Spectrophotometry of HD16538 and HR: 8210 Ik-Pegasi . In: Monthly Notices of the Royal Astronomical Society . tape 270 , no. 3 , 1994, p. 516 , bibcode : 1994MNRAS.270..516B .
  4. ^ Roger John Tayler: The Stars: Their Structure and Evolution . Ed .: Cambridge University Press. 1994, ISBN 0-521-45885-4 , pp. 16 .
  5. ↑ a b c d e f g D. Wonnacott, BJ Kellett, B. Smalley, C. Lloyd: Pulsational Activity on Ik-Pegasi . In: Monthly Notices of the Royal Astronomical Society . tape 267 , no. 4 , 1994, pp. 1045-1052 , bibcode : 1994MNRAS.267.1045W .
  6. ↑ a b c d e W. Landsman; T. Simon .; P. Bergeron: The hot white-dwarf companions of HR 1608, HR 8210, and HD 15638 . In: Publications of the Astronomical Society of the Pacific . tape 105 , no. 690 , 1999, ISSN  0004-6280 , p. 841-847 , doi : 10.1086 / 133242 , bibcode : 1993PASP..105..841L .
  7. ^ Hans Krimm: Luminosity, Radius and Temperature. (No longer available online.) Hampden-Sydney College, August 19, 1997, archived from the original on May 8, 2003 ; accessed on January 29, 2010 (English).
  8. ↑ a b c B. Smalley, KC Smith, D. Wonnacott, CS Allen: The chemical composition of IK Pegasi . In: Monthly Notices of the Royal Astronomical Society . tape 278 , no. 3 , 1996, p. 688-696 , bibcode : 1996MNRAS.278..688S .
  9. ^ A b S. Vennes, DJ Christian, JR Thorstensen,: Hot White Dwarfs in the Extreme-Ultraviolet Explorer Survey. IV. DA White Dwarfs with Bright Companions . In: The Astrophysical Journal . tape 502 , no. 2 , 1998, p. 763-787 , doi : 10.1086 / 305926 .
  10. ↑ John Vallerga: The Stellar Extreme-Ultraviolet Radiation Field . In: Astrophysical Journal . tape 497 , 1998, pp. 77-115 , doi : 10.1086 / 305496 .
  11. ↑ a b c d D. Wonnacott, BJ Kellett, DJ Stickland: Peg - A nearby, short-period, Sirius-like system . In: Monthly Notices of the Royal Astronomical Society . tape 262 , no. 2 , 1993, ISSN  0035-8711 , p. 277-284 , bibcode : 1993MNRAS.262..277W .
  12. ^ Edward Charles Pickering: Revised Harvard photometry: a catalog of the positions, photometric magnitudes and spectra of 9110 stars, mainly of the magnitude 6.50, and brighter observed with the 2 and 4 mm meridian photometers . In: Annals of the Astronomical Observatory of Harvard College . tape 50 , 1908, pp. 182 , bibcode : 1908AnHar..50 .... 1P .
  13. ^ Spectroscopic Binaries. University of Tennessee, accessed January 29, 2010 .
  14. ↑ WE Harper: The orbits of A Persei and HR 8210 . In: Publications of the Dominion Astrophysical Observatory . tape 4 , 1927, pp. 161-169 , bibcode : 1927PDAO .... 4..161H .
  15. ↑ MAC Perryman, L. Lindegren, J. Kovalevsky, E. Hoeg, U. Bastian, PL Bernacca, M. Crézé, F. Donati, M. Grenon, F. van Leeuwen, H. van der Marel, F. Mignard, CA Murray, RS Le Poole, H. Schrijver, C. Turon, F. Arenou, M. Froeschlé, CS Petersen: The HIPPARCOS Catalog . In: Astronomy and Astrophysics . tape 323 , 1997, pp. L49 – L52 , bibcode : 1997A & A ... 323L..49P .
  16. ↑ Steven R. Majewski: Stellar Motions. University of Virginia, 2006, accessed August 4, 2018 .
  17. ↑ Ralph Elmer Wilson: General catalog of stellar radial velocities . Ed .: Carnegie Institution of Washington. 1953 bibcode : 1953QB901.W495 ..... .
  18. ↑ MR Burleigh, MA Barstow, HE Bond, JB Holberg: Proceedings 12th European Workshop on White Dwarfs . Resolving Sirius-like Binaries with the Hubble Space Telescope. Ed .: Astronomy Society of the Pacific. San Francisco 1975, ISBN 1-58381-058-7 , pp. 222 , arxiv : astro-ph / 0010181 , bibcode : 2001ASPC..226..222B (edited by: JL Provencal, HL Shipman, J. MacDonald, S. Goodchild).
  19. ↑ a b A. Gautschy, H. Saio: Stellar Pulsations Across The HR Diagram: Part 1 . In: Annual Review of Astronomy and Astrophysics . tape 33 , 1995, pp. 75–114 , doi : 10.1146 / annurev.aa.33.090195.000451 , bibcode : 1995ARA & A..33 ... 75G .
  20. ^ Matthew Templeton: Variable Star of the Season: Delta Scuti and the Delta Scuti variables. AAVSO, 2004, accessed August 13, 2018 .
  21. ^ Gene Smith: Stellar Spectra. University of California, San Diego Center for Astrophysics & Space Sciences, April 16, 1999, accessed January 29, 2010 .
  22. ↑ JG Mayer, J. Hakkila: Photometric Effects of Binarity on Am Star Broadband Colors . In: Bulletin of the American Astronomical Society . tape 26 , 1994, pp. 868 , bibcode : 1994AAS ... 184.0607M .
  23. ^ Stellar Lifetimes. Georgia State University, 2005, accessed January 29, 2010 .
  24. ↑ The explanation for the colors of the star can be found under: The Color of Stars. (No longer available online.) Australia Telescope Outreach and Education, December 21, 2004, archived from the original on February 22, 2012 ; accessed on January 29, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / outreach.atnf.csiro.au
  25. ↑ Staff: White Dwarfs & Planetary Nebulas. Harvard-Smithsonian Center for Astrophysics, September 26, 2008, accessed January 29, 2010 .
  26. ^ A. Heger .; CL Fryer; SE Woosley; N. Langer .; DH Hartmann: §3, How Massive Single Stars End Their Life . In: Astrophysical Journal . tape 591 , no. 1 , 2003, p. 288–300 , doi : 10.1086 / 375341 , arxiv : astro-ph / 0212469 , bibcode : 2003ApJ ... 591..288H .
  27. ^ Courtney Seligman: The Mass-Luminosity Diagram and the Lifetime of Main-Sequence Stars. 2007, accessed January 29, 2010 .
  28. ↑ Staff: Stellar Evolution - Cycles of Formation and Destruction. Harvard-Smithsonian Center for Astrophysics, March 17, 2008, accessed January 29, 2010 .
  29. ↑ Michael Richmond: Late stages of evolution for low-mass stars. Rochester Institute of Technology, October 5, 2006, accessed January 29, 2010 .
  30. ↑ David Darling: Carbon burning. The Internet Encyclopedia of Sciences, accessed January 29, 2010 .
  31. ↑ D. Savage; T. Jones; Ray Villard; M. Watzke: Hubble Separates Stars in the Mira Binary System. HubbleSite News Center, August 6, 1997; accessed January 29, 2010 .
  32. ↑ H. Oberhummer; A. Csótó; H. Schlattl: Stellar Production Rates of Carbon and Its Abundance in the Universe . In: Science . tape 289 , no. 5476 , July 7, 2000, pp. 88-90 , doi : 10.1126 / science.289.5476.88 , PMID 10884230 ( online [accessed January 29, 2010]).
  33. ^ Icko Iben Jr .: Single and binary star evolution . In: Astrophysical Journal Supplement Series . tape 76 , May 26, 1991, ISSN  0067-0049 , pp. 55–114 , doi : 10.1086 / 191565 , bibcode : 1991ApJS ... 76 ... 55I .
  34. ↑ P. Gil-Pons; E. García-Berro: On the formation of oxygen-neon white dwarfs in close binary systems . In: Astronomy and Astrophysics . tape 375 , 2001, p. 87–99 , doi : 10.1051 / 0004-6361: 20010828 , arxiv : astro-ph / 0106224 , bibcode : 2001astro.ph..6224G .
  35. ^ SE Woosley; A. Heger: The Evolution and Explosion of Massive Stars . In: Reviews of Modern Physics . tape 74 , no. 4 , November 7, 2002, p. 1015-1071 , doi : 10.1103 / RevModPhys.74.1015 ( PDF [accessed January 29, 2010]).
  36. ↑ JB Holberg, MA Barstow, FC Bruhweiler, AM Cruise, AJ Penny: Sirius B: A New, More Accurate View . In: The Astrophysical Journal . tape 497 , no. 2 , 1998, p. 935-942 , doi : 10.1086 / 305489 .
  37. ↑ Estimating Stellar Parameters from Energy Equipartition. ScienceBits, accessed January 29, 2010 .
  38. ↑ G. Chabrier, P. Brassard, G. Fontaine, D. Saumon: Cooling Sequences and Color-Magnitude Diagrams for Cool White Dwarfs with Hydrogen Atmospheres, in: Astrophysical Journal 543, p.216 ff . 2000.
  39. ↑ KA Postnov, LR Yungelson: The Evolution of Compact Binary Star Systems. (No longer available online.) Living Reviews in Relativity, 2006, archived from the original September 26, 2007 ; accessed on January 29, 2010 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / relativity.livingreviews.org
  40. ↑ N. Langer; A. Deutschmann; S. Wellstein; P. Höflich: The evolution of main sequence star + white dwarf binary systems towards Type Ia supernovae . In: Astronomy and Astrophysics . tape 362 , 2000, pp. 1046-1064 , arxiv : astro-ph / 0008444 , bibcode : 2000astro.ph..8444L .
  41. ↑ K. Malatesta; K. Davis: Variable Star Of The Month: A Historical Look at Novae. (PDF) AAVSO, May 2003, accessed on August 13, 2018 (English).
  42. ↑ Kerri Malatesta: Variable Star Of The Month — May, 2000: RS Ophiuchi. (PDF) AAVSO, May 2000, accessed on August 11, 2018 (English).
  43. ^ Susan Hendrix: Scientists see Storm Before the Storm in Future Supernova. NASA, July 20, 2007, accessed January 29, 2010 .
  44. ↑ N. Langer; S.-C. Yoon; S. Wellstein; S. Scheithauer: The Physics of Cataclysmic Variables and Related Objects, ASP Conference Proceedings . On the evolution of interacting binaries which contain a white dwarf. Ed .: Astronomical Society of the Pacific. San Francisco, California 2002, ISBN 1-58381-101-X , pp. 252 , bibcode : 2002ASPC..261..252L (arranged by: Gänsicke, BT; Beuermann, K .; Rein, K.).
  45. ^ Rosanne Di Stefano: Proceedings of the International Workshop on Supersoft X-Ray Sources . Luminous Supersoft X-Ray Sources as Progenitors of Type Ia Supernovae. Ed .: Springer-Verlag. Garching (Germany) 1997, ISBN 3-540-61390-0 , arxiv : astro-ph / 9701199 ( PDF [accessed on January 30, 2010] editor: J. Greiner).
  46. ^ CL Fryer, KC New: Gravitational Waves from Gravitational Collapse. In: Living Reviews in Relativity. Volume 6, number 1, 2003, p. 2, doi: 10.12942 / lrr-2003-2 , PMID 28163639 , PMC 5253977 (free full text) (review).
  47. ↑ Staff: Stellar Evolution - Cycles of Formation and Destruction. Harvard-Smithsonian Center for Astrophysics, August 29, 2006, accessed January 30, 2010 .
  48. ↑ a b Neil Gehrels; Claude M. Laird; Charles H. Jackman; John K. Cannizzo; Barbara J. Mattson; Wan Chen: Ozone Depletion from Nearby Supernovae . In: The Astrophysical Journal . tape 585 , no. 2 , 2003, p. 1169–1176 , doi : 10.1086 / 346127 , arxiv : astro-ph / 0211361 , bibcode : 2003ApJ ... 585.1169G .
  49. ^ Brad MS Hansen: Type Ia Supernovae and High-Velocity White Dwarfs . In: The Astrophysical Journal . tape 582 , no. 2 , 2003, p. 915–918 , doi : 10.1086 / 344782 , arxiv : astro-ph / 0206152 , bibcode : 2002astro.ph..6152H .
  50. ↑ E. Marietta; A. Burrows; B. Fryxell: Type Ia Supernova Explosions in Binary Systems: The Impact on the Secondary Star and Its Consequences . In: The Astrophysical Journal Supplement Series . tape 128 , 2000, pp. 615-650 , doi : 10.1086 / 313392 .
  51. ^ Staff: Introduction to Supernova Remnants. NASA / Goddard, October 4, 2007, accessed January 30, 2010 .