AB Doradus

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Double star
AB Doradus
Position of AB Doradus in the night sky
Position of AB Doradus in the night sky
Observation
dates equinoxJ2000.0 , epoch : J2000.0
AladinLite
Constellation Swordfish
Right ascension 5 h 28 m 44.8 s
declination −65 ° 26 ′ 54.9 ″
Astrometry
Radial velocity +28 km / s
parallax (66.9 ± 0.5) mas
distance  (48.7 ± 0.4) ly
((14.9 ± 0.1) pc )
Absolute visual brightness M vis 6.055 mag
Absolute bolometric magnitude M bol 5.88 likes
Proper movement :
Rec. Share: 32.14 mas / a
Dec. portion: 150.97 mas / a
orbit 
period C to A: 11.75  a
Bb to Ba: ~ 1  a
B to AC: ~ 1570  a
Major semi-axis C to A: 2.3  AI
Bb to Ba: ~ 1  AI
B to AC: 135  AI
Individual data
Names 0A / C0 ; Ba / Bb
Observation data:
Apparent brightness 0A / C0 6.93 mag / 19.80 mag
Ba / Bb 13.91 mag / 14.50 mag
Typing:
Spectral class 0A / C0 K2 Vk / M8
Ba / Bb M5 Ve / M5.5 Ve
B − V color index 0A / C0 +0.83
U − B color index 0A / C0 +0.37
Physical Properties:
Absolute vis.
Brightness
M vis
0A / C0 6.06 mag / 18.93 mag
Ba / Bb 13.04 mag / 13.63 mag
Absolute bol.
Brightness
M bol
0A / C0 5.89 mag / 16.38 mag
Ba / Bb 11.68 mag / 12.17 mag
Dimensions 0A / C0 0.76 M / 0.089 M
Ba / Bb 0.165 M / 0.145 M
radius 0A / C0 0.9 R / ~ 0.16 R
Ba / Bb 0.18 R / 0.18 R
Luminosity 0A / C0 0.377 L / 0.000024 L
Ba / Bb 0.00182 L / 0.00116 L
Effective temperature 0A / C0 4900 K / 2640 K
Ba / Bb 3225 K / 3160 K
Rotation time 0A / C0 0.514 d / 0.4 d
Ba / Bb 6.8 d / 6.8 d
Age about 50 million years
Other names
and catalog entries
Cordoba Survey CD −65 ° 332
Henry Draper Catalog HD 36705 [1]
SAO catalog SAO 249286 [2]
Tycho catalog TYC 8887-1611-1 [3]
Hipparcos catalog HIP 25647 [4]
WDS catalog WDS J05287-6527
Further designations: AB Doradus, Rst 137

AB Doradus (abbreviated AB Dor ) is a four-fold star system in the constellation Swordfish ( Latin Dorado ), about 49  light-years away , located in the southern sky . It contains a rapidly rotating main sequence star ( AB Doradus A ), which, despite its hundred times the diameter of the earth, rotates around its own axis in just twelve hours, as well as three red dwarf stars ( AB Doradus Ba , AB Doradus Bb and AB Doradus C ). AB Doradus C is one of the lightest known stars - its mass is just above the limit of the brown dwarf .

The apparent magnitude of AB Doradus A changes with a period equal to its time of revolution. So the star belongs to the rotationally variable . Its variability is attributed to large star spots that are related to its complex magnetic field. Observations showed an amplitude of the change in brightness varying between about 0.01 and 0.05 mag.

The brightness fluctuations of AB Doradus A gave the system its name: The first part of the name, "AB", follows the rules for naming variable stars and says that AB Doradus is the 56th star in the constellation Swordfish where variability could be demonstrated. The second part of the name "Doradus" is the genitive of the Latin name of the constellation. The third part "A" of the main component was added later to distinguish it from the smaller companions discovered later.

AB Doradus is only 50 million years old and namesake of the AB Doradus movement cluster , which u. a. to further clarify star formation is being researched.

Find in the night sky

For observers in the southern hemisphere , AB Doradus can be seen almost all year round. However, the star can not be observed even from the southernmost parts of Europe .

Due to its low apparent brightness, the star cannot be seen with the naked eye . However, even a small telescope or binoculars is sufficient to observe it. Near AB Doradus is the Large Magellanic Cloud (the largest satellite galaxy in the Milky Way ) and the constellations Netz (Reticulum) and Table Mountain (cafeteria).

position

distance

The distance from AB Doradus can be determined relatively accurately to 49 light years due to its strong proper motion and the relatively large parallax .

The 500 stars closest to the Sun are (with correct parallax) in an area of ​​33 light years. From this it follows (assuming constant star density) by simple calculation that the components of AB Doradus belong to the 1,600 to 1,700 stars closest to the Sun.

AB Doradus appears to be part of the Large Magellanic Cloud standing next to him in the sky. However, at a distance of 160,000 light years, it is approx. 3000 times further from the sun than AB Doradus.

Proper movement

A comparison of the proper motion with that of other stars showed some striking similarities. The star system AB Doradus, which is only 50 million years old, gave its name to the AB Doradus cluster of movements . It is a young moving cluster with a loose group of stars , which are not characterized by a spatial concentration around a cluster center, but by a common direction of movement towards a convergence or vanishing point .

Joint creation with the Pleiades?

During the investigation of the age of AB Doradus, a noticeable similarity with respect to the proper movement of the movement cluster with the Pleiades was found. The Pleiades are also a young open star cluster that can be observed as the "seven stars" in the constellation Taurus . This knowledge led to an investigation of the space velocity or the movement within the Milky Way. It should be used to determine whether the two groups originated in the same gas cloud.

At the moment, AB Doradus and the Pleiades are 475 light years apart. With the help of the observation data, it was possible to simulate the movement of the two groups of stars over the past million years. The result says that the distance between AB Doradus and the Pleiades 125 million years ago (i.e. at the time when the first stars of the moving clusters began to shine) was significantly greater at 850 light years. This refuted the hypothesis that AB Doradus was formed in the same (probably 160 light-years wide) molecular gas cloud as the Pleiades. Nevertheless, the self-movements do not rule out a larger region of origin.

Structure of the system

AB Doradus is a multiple star system, which is composed of two binary star systems which orbit each other around a common barycenter at a distance of about 135 astronomical units , which corresponds to 135 times the distance between the earth and the sun .

The lower-mass binary star system contains the two stars AB Doradus Ba and AB Doradus Bb , which orbit each other with a period of about 135 days. The heavier binary star system, on the other hand, is called "AB Doradus A – C" and thus contains the components AB Doradus A and AB Doradus C , which revolve every 11.75 years at a distance of 2.3 AU. Because of its higher mass, the distance to the common barycentre AB Doradus is about half as great as that of the lighter double star AB Doradus B.

Components of the system

AB Doradus A – C

Infrared close-up of AB Doradus A – C, the yellow dashed line marks the orbit of C

AB Doradus A

AB Doradus A, the main star shining orange, is a sun-like star of the spectral type K2 Vk. The numerical designation ranges from 0 (hottest) to 9 (coolest) star within the spectral class K; with K2, AB Doradus A belongs to the hotter K stars , like α Centauri B or ε Eridani . The luminosity class  V indicates that it belongs to the main sequence stars . Due to its young age, AB Doradus A is often referred to as a pre-main sequence star (“pre-main sequence star”), ie a star that has not yet reached the main sequence or has only just reached it. The suffix "k" stands for interstellar absorption lines.

The mass of AB Doradus A is three quarters of the solar mass. This makes it by far the heaviest component of the four-star system. As an early K star, it has a surface temperature of 4900  K and is therefore only less than 900 K cooler than the sun. But this small difference in effective temperature makes a big difference in terms of luminosity. Although AB Doradus A has a relatively large surface area with 0.9 times the sun's diameter, it results in just over a third of the sun's luminosity . In addition, due to its surface temperature of approx. 5800 K, the sun shines almost completely in visible light , while with AB Doradus A the proportion of infrared radiation is significantly higher. Thus, only about 85% of the total luminosity of AB Doradus A is due to visible light. This weaker visual luminosity is the reason that the orange dwarf can no longer be seen with the naked eye, despite the relatively short distance of almost fifty light years with an apparent brightness of 6.93 mag.

rotation

In the 1990s, measurements of the width of its spectral lines showed that AB Doradus A rotates very quickly around its own axis, which results in bulges at the equator , a much more complex magnetic field and temperature fluctuations on the surface. This is the reason why AB Doradus A was assigned to other spectral types.

It has been found that a full axis rotation at the equator takes about twelve hours. This corresponds to fifty times the angular speed of the sun, which takes 25 days for a full rotation, or twice the angular speed of the earth, although its diameter is only one hundredth of AB Doradus A. This makes the orange star's rotation time one of the shortest of all known stars; Wega , Altair or Achernar also achieve similarly high rotation speeds . However, AB Doradus A is still a long way from breaking apart due to the centrifugal forces that occur. This limit would presumably only be exceeded from an equatorial rotation speed of 450 km / s.

In addition, eruptions were detected on the surface of AB Doradus A; The weak hydrogen plasma is heated to up to fifteen million degrees and enclosed in the magnetic fields that curve spherically over the star's surface. This plasma glows in X-rays . This makes AB Doradus A one of the brightest stellar X-ray sources in the sky due to its short distance. Equatorial eruptions rotate much faster than those at the poles due to differential rotation , but the difference in 1988 and 1996 was only half as great as between 1992 and 1995. In these years the star appeared strongly flattened.

Further development

At the moment, AB Doradus A is still at the beginning of his life. As in all sun-like stars, the fusion of hydrogen to helium in the nucleus takes place mainly via the proton-proton chain , which does not create a steep temperature gradient . Thus, the heat radiation dominates inside sun-like stars. In the outer part, on the other hand, convection prevails, because here the star is cool enough so that the hydrogen is neutral and thus impermeable to ultraviolet photons (see also article Star structure ).

Because non-fusible helium ash accumulates in the core, the decrease in hydrogen per unit mass leads to a gradual decrease in the rate of nuclear fusion within that mass. To compensate for this, the core temperature and pressure increase slowly, which causes an increase in the overall fusion rate. This leads to a steady increase in the luminosity and radius of AB Doradus A over time. For example, the luminosity of the young sun was only around 70% of its current value. The increase in luminosity thus gradually changes the position of the star in the Hertzsprung-Russell diagram over time .

In about 22 billion years, the hydrogen supply in the core of AB Doradus A will be exhausted. Then the gravitational collapse is resumed due to the loss of energy production. The hydrogen surrounding the core reaches the temperature and pressure necessary to fuse. This creates a hydrogen-burning shell around the helium core. As a result of these changes, the outer shell expands, the temperature drops, and the star turns into a red giant .

At this point the star leaves the main sequence and reaches the giant branch. The star's helium core continues to contract until it is stopped by what is known as degenerate electron pressure - a quantum mechanical effect that limits the extent to which matter can be compressed.

Since AB Doradus A is a star with more than half the mass of the Sun, the core can reach a temperature at which it becomes possible for carbon to be produced from helium via the three-alpha process . At the end of this process, AB Doradus A will shed its outer shells and form planetary nebulae . What remains is the extinct core in the form of a white dwarf , which only glows in the form of thermal radiation and cools down slowly. The remaining star becomes reddish until it finally disappears completely as a black dwarf in the visible area.

AB Doradus C

AB Doradus C is at the end of the main row of the HR diagram (ESO graphic)
The "wobbling" of A , due to the joint movement around the barycentre of A and C.
The orbit of AB Doradus C around the more massive AB Doradus A shown as a green ellipse

AB Doradus C is the smaller component of the AB Doradus AC subsystem. The red dwarf belongs to the spectral class M8 and is therefore classified as a later M dwarf star . At 2600 Kelvin, its surface temperature is correspondingly cool, while that of the sun is more than twice as high. Its radius, which is only about a sixth of AB Doradus A, is just as small.

With 8.9% of the solar mass (approx. 93 Jupiter masses ), AB Doradus C is one of the lightest known stars. If he were just a little less massive, he would be a brown dwarf . Such objects occupy a special position between planets and stars. They can briefly gain small amounts of energy from the fusion of deuterium before they cool down. In this initial phase they can hardly be distinguished from normal stars.

While the sun and AB Doradus A are the average main sequence stars below the center of the main sequence in the Hertzsprung-Russell diagram, AB Doradus C, the lowest-mass of all stars, if the cooler brown dwarfs are not taken into account, marks the end.

discovery

The little companion of AB Doradus A was already known in the 1990s, until 2004 it could only be detected due to its gravitational effect by a "wobbling" of the circled AB Doradus A, which completely outshines it. This wobbling comes about through the rotation around the common barycentre. The new component was called AB Doradus  C because the name AB Doradus B was already taken. The name AB Doradus Ab was also ruled out because otherwise the main orange star, which had made a name for itself due to its unusual rotation , would have had to be renamed AB Doradus Aa .

Since AB Doradus C could not be optically captured by the Hubble Space Telescope, it was not captured optically until 2005 with the NACO SDI instrument of the Very Large Telescope of the European Southern Observatory . The camera, equipped with adaptive optics, took four pictures of AB Doradus A – C simultaneously through different filters. So that the brighter AB Doradus A disappeared and the cooler companion became visible, the images were subtracted from one another. The fact that the two stars have their maximum brightness in different spectral ranges, AB Doradus A in visible light, AB Doradus C in the infrared wave range was used.

With the help of the new observations it was found that AB Doradus A is orbited by its companion in a highly eccentric orbit. This means that the center of the orbit of AB Doradus C is outside the common barycentre of the two stars, and that they are thus at a varying distance from each other.

It was also found that AB Doradus C 2600  K to 400 K was cooler than expected. This calls into question previous models for calculating star masses from luminosities for small celestial objects insofar as they have to be adapted for small stars in order to explain the observation result.

The ESO images below show the AB Doradus A – C system before and after using the new observation method. While the weak component is still completely outshone in the left picture, it is clearly recognizable on the right picture, aided by the "disappearance" of AB Doradus A.

The system AB Doradus A and C before the application of the new observation method (left) and afterwards
Further development

As in sun-like stars, a red dwarf like AB Doradus C fuses hydrogen to helium via the proton-proton reaction. However, since this star class also has low core temperatures, convection prevails in the entire star, it is considered "fully convective", while in heavy and average main sequence stars the heat radiation is part of the energy transfer in the star structure to the outside.

The assumed lifespan of red dwarfs on the main sequence in trillion years

In larger stars, helium accumulates in the core over time. Instead, this is not the case with the fully convective red dwarfs. Therefore, they can fuse more hydrogen percentages before they leave the main sequence, which is what gives them their enormous lifespan. The lower the mass of the star, the longer it is on the main sequence. This means that AB Doradus C, the lightest star, will remain on the main sequence longer than any other known star, possibly even ten billion years.

It is still uncertain that AB Doradus C will ultimately reach this enormous age. If its orbit around AB Doradus A does not stabilize in the next billions of years, there will be a mass transfer between the two stars during the phase of AB Doradus A as a red giant. Then matter flows from the giant star crossing the Roche border to the small component. The increasing mass of AB Doradus C would then favor a higher reaction activity, whereby the fuel would be consumed faster and the formerly small red dwarf would go out after a few trillion years.

Due to its small mass, AB Doradus C will not swell into a red giant itself. Instead, the star will shrink as soon as the hydrogen supply in the star is exhausted and the gravitational energy released will enable the final fusion processes. Eventually AB Doradus C reaches the stage of the white dwarf.

AB Doradus Ba and Bb

Artist's impression of a red dwarf (NASA illustration)

According to the results, AB Doradus Ba and AB Doradus Bb only make up one percent of the luminosity of AB Doradus A if the results are correct.

AB Doradus Ba is the heavier component of the AB Doradus B system, with an estimated 13 to 20% of the solar mass. Initially, the star was classified as brighter, but could later be assigned to the M5 V spectral class. Its surface temperature is between 3145 and 3305 Kelvin . On the other hand, the weaker AB Doradus Bb, which makes up 11 to 18% of the solar mass, was determined to be 3080 K to 3240 K. This means it belongs to the somewhat cooler M5.5 V spectral class.

Like AB Doradus C, AB Doradus Ba and AB Doradus Bb will clearly outlive the main component AB Doradus A many times over and ultimately also end up as white dwarfs.

Discoveries

The component B of AB Doradus was discovered by Richard A. Rossiter , who included the double star as number 137 in his catalog; accordingly, component B is known today as Rossiter 137 B or Rst 137 B for short . It was originally assumed that the small companion ten arcseconds away from AB Doradus A is a single star of the thirteenth magnitude of the spectral class M3.5 Ve. The suffix "e" stands for emission lines .

Since the detection of the small AB Doradus C, however, it has been possible to determine using the new observation methods that AB Doradus B consists of two red dwarf stars that orbit each other at a distance comparable to the distance between the sun and the earth. The new components were given the names AB Doradus Ba and AB Doradus Bb . Using the mass-luminosity law, a total mass of the two stars of one third of the solar mass can be determined.

Age determination

With the help of the determined physical properties of AB Doradus Ba and AB Doradus Bb, the age of the AB Doradus system should be determined more precisely. An exact result was not possible due to the unusual properties of AB Doradus A and AB Doradus C.

The two orbiting little red stars with three other red dwarfs of the spectral class M3 of the AB Doradus cluster were compared with other M dwarfs from the more than 100 million year old Pleiades and the open one, which has existed for 50 to 60 million years Star cluster IC 2391, the region around ο Velorum in the constellation Sail of the Ship , compared. On the diagram, the similarities of the examined stars pointed in the direction of the younger cluster IC 2391. This means that the age of AB Doradus could be determined to be at least 50 million years.

Possibility of planet formation

With the discovery of the three super-earths around HD 40307 , the theory was put forward that there could be planets around almost any star. With the discovery of a planet in the binary star system γ Cephei, AB Doradus moved into the field of view of the possible candidates for the accommodation of a potential planetary system. The habitable zones of the individual components can be calculated from the luminosity of the stars and their size. This life zone marks the distance between a planet and its central star so that water can be permanently present on the surface in liquid form as a prerequisite for life, comparable to earthly conditions.

Comparison of important stellar parameters
Surname Spectral class Mass
[M ]
Luminosity
[L ]
Life zone
[AE]
AB Doradus A K2 Vk 0.76 0.377 0.61
AB Doradus Ba M5 V 0.165 0.00182 0.04
AB Doradus port M5.5 V 0.145 0.00116 0.03
AB Doradus C M8 0.089 > 1/1000 > 0.01
Sun G2 V 1.0 1.0 1.0

In theory, a planet around AB Doradus A at a distance from Venus to the sun could receive enough energy to salvage liquid water. The main problem, which clearly limits the formation of planets, is the fact that AB Doradus is a double binary star system. While single stars can easily form dust disks, the stars in a binary system often hinder each other. In order to ensure stable orbits of the planets, the two stars of a system must either orbit each other so closely that one planet moves its orbit around the barycenter of the stars, or the stars orbit each other at such a great distance that the orbits of the planets around the individual stars are not disturbed.

AB Doradus A has the most sun-like properties, but possible planets could not remain stable in their orbit due to the enormous eccentricity of the orbit of AB Doradus C. In addition, there is the high X-ray and magnetic activity of the rapidly rotating AB Doradus A, which means that the chance of planet formation at a smaller distance around the orange star is also zero. The faint red dwarf is also hardly suitable, as a fictional planet would have to move around the star on an extremely small orbit. In addition, the varying proximity of the more luminous AB Doradus A would severely limit the climatic conditions.

Thus only the two red dwarf stars AB Doradus Ba and AB Doradus Bb remain as possible central stars of extrasolar planets. Since their respective life zones are only a twenty-fifth of the distance between the two stars, planets of low mass, i.e. terrestrial planets, could easily form without being helplessly exposed to the forces of the second star. Gas giants such as Jupiter and Saturn , which cannot form in a binary star system due to the gravitational disturbances , can thus be safely ruled out .

The habitability of red dwarf planets has been the subject of some debate. Despite their abundance and the long lifespan of these stars, there are several factors that could make life on such a planet difficult. Transferred to AB Doradus Ba and AB Doradus Bb, a planet should only orbit one of the two stars at a distance of 10% of the distance between the planet Mercury and the sun. When a planet orbits this close to a star, the tidal forces would create a bound rotation. One side of the surface would always face the star, so the red sun would always be seen in the same place in the sky. Even if the rotation were to remain unrestricted, no seasons could develop, since one orbit of a planet within the life zone would take a few days.

Furthermore, since flare outbreaks usually occur in red dwarfs, this would hardly make life possible. Within a few minutes, the star's luminosity could double or even triple. These flares could destroy the atmosphere of any planet that is in the habitable zone.

The sky over AB Doradus

Although the AB Doradus system is barely 50 light-years away, the sky appears largely completely changed to an observer. Only some constellations like the ship's keel and the dragon look almost unchanged. However, the constellation Swordfish appears completely straightened out. In contrast, the sun is an inconspicuous star of the sixth magnitude in the dragon, near Aldhibah (ζ Draconis), antipodal (in the opposite direction) to the position of AB Doradus as seen from the earth, i.e. at the coordinates α = 17 h 28 m 45 s and δ = + 65 ° 26 '55 " . 1728452652655

Stars closer to the sun such as Sirius , Prokyon and Alpha Centauri can be seen in clearly shifted and approximate positions. For example, Sirius does not have the same brightness of −1.46 mag, it is just a second magnitude star, comparable to the other parts of the big dog like Aludra (2.42 mag) or Wezen (1.78 mag). Instead, Canopus shines as the brightest and only point of light that exceeds the −1 mag limit, followed by Achernar and the two main stars of Orion , Betelgeuse and Rigel . In addition, the only eight light-years away HD 40307 forms an apparent orange double star with Pollux . The Zeta Reticuli system also appears in the sky as a yellow double of the third magnitude, only 14 light-years away.

The weak direct neighbors from AB Doradus' cluster of movements adorn the sky as orange-reddish, only faintly recognizable stars, which themselves never appear conspicuously and, due to their identical movement, hardly change their position in the sky.

See also

Web links

Commons : AB Doradus  - collection of images, videos and audio files

Remarks

  1. Conversion of parallax into light years:
  2. π and 4/3 are abbreviated:
  3. a b AB Doradus: U = −7.7 ± 0.4 km / s; V = -26.0 ± 0.4 km / s; W = −13.6 ± 0.3 km / s
  4. Pleiades: U = −6.6 ± 0.4 km / s; V = -27.6 ± 0.3 km / s; W = −14.5 ± 0.3 km / s
  5. a b The lifetime of a star on the main sequence can be estimated:

Individual evidence

  1. a b c d e f SIMBAD Query Result: V * AB Dor - Rotationally variable Star. Center de Données astronomiques de Strasbourg, accessed on February 3, 2009 .
  2. a b c d e Perryman, MAC et al .: The Hipparcos Catalog. European Space Agency, accessed on February 3, 2009 (type in '25647' in the 'Hipparcos Identifier' field and click on 'Retrieve').
  3. a b c d e Jürgen Kummer: Special stars: AB Doradus. Internet service Kummer + Oster GbR, accessed on February 3, 2009 .
  4. a b c d e Markus Janson, Wolfgang Brandner, Rainer Lenzen, Laird Close, Eric Nielsen, Markus Hartung, Thomas Henning, Hervé Bouy: Improved age constraints for the AB Dor quadruple system - The binary nature of AB Dor B . In: Astronomy & Astrophysics . November 20, 2006, arxiv : astro-ph / 0611616 (English).
  5. ^ JL Innis, K. Thompson, DW Coates, T. Lloyd Evans: Observations of active-chromosphere stars. II - Photometry of AB Dor, 1978-1987 . In: Royal Astronomical Society, Monthly Notices ( ISSN  0035-8711 ) . 235, 1988, pp. 1411-1422. bibcode : 1988MNRAS.235.1411I .
  6. a b AB Doradus A - Orange Main Sequence Star ( Memento from December 16, 2010 in the Internet Archive )
  7. LM Close, R. Lenzen, JC Guirado, EL Nielsen, EE Mamajek, W. Brandner, M. Hartung, C. Lidman, B. Biller: A dynamical calibration of the mass-luminosity relation at very low stellar masses and young ages . In: Nature . January 20, 2005, bibcode : 2005Natur.433..286C (English).
  8. J.-F. Donati, A. Collier Cameron, M. Semel, BD Carter, DE Rees: Spectropolarimetric observations of active stars . Ed .: The Royal Astronomical Society. November 1997, bibcode : 1997MNRAS.291..658D (English).
  9. J.-F. Donati, A. Collier Cameron, M. Semel, GAJ Hussain: Magnetic topology and prominence patterns on AB Doradus . Ed .: The Royal Astronomical Society. January 1999, bibcode : 1999MNRAS.302..437D (English).
  10. KM Hiremath: Internal Rotation of AB Doradus. (PDF; 201 kB) Indian Space Institute of Astrophysics, accessed on March 10, 2009 (English).
  11. ^ J. Sanz-Forcada, A. Maggio, G. Micela: Three years in the coronal life of AB Dor. I. Plasma emission measure distributions and abundances at different activity levels . September 2003, doi : 10.1051 / 0004-6361: 20031025 , bibcode : 2003A & A ... 408.1087S (English).
  12. Stephen A. Drake: What are the (apparently) brightest X-ray sources in the sky as seen from the Earth? Retrieved May 27, 2009 .
  13. ^ Carl J. Hansen, Steven D. Kawaler, Virginia Trimble: Stellar interiors. Physical principles, structure, and evolution . Ed .: Springer. 2nd Edition. 2004, ISBN 0-387-20089-4 , pp. §5.1.1 .
  14. Donald D. Clayton: Principles of Stellar Evolution and Nucleosynthesis . University of Chicago Press, 1983, ISBN 0-226-10953-4 (English).
  15. ^ DO Gough: Solar interior structure and luminosity variations . In: Solar Physics . 74, 1981, pp. 21-34. bibcode : 1981SoPh ... 74 ... 21G . doi : 10.1007 / BF00151270 .
  16. Hans OU Fynbo, et al : Revised rates for the stellar triple-α process from measurement of 12C nuclear resonances . In: Nature . 433, 2004, pp. 136-139. doi : 10.1038 / nature03219 .
  17. Stellar Structure and Evolution ( Memento from August 23, 2009 in the Internet Archive )
  18. ^ Staff: Post-Main Sequence Stars . Australia Telescope Outreach and Education. October 12, 2006. Retrieved March 11, 2009.
  19. A scale for underweight stars ( Memento from June 12, 2007 in the Internet Archive )
  20. Spectrum of Science . May 2005, p. 23-26 .
  21. Fred C. Adams, Gregory Laughlin, Genevieve JM Graves: Red Dwarfs and the End of the Main Sequence . In: Gravitational Collapse: From Massive Stars to Planets . Revista Mexicana de Astronomía y Astrofísica, December 2004, p. 46–49 , bibcode : 2004RMxAC..22 ... 46A .
  22. Fred C. Adams, Gregory Laughlin: A Dying Universe. The Long Term Fate and Evolution of Astrophysical Objects . 1996, arxiv : astro-ph / 9701131v1 .
  23. For a detailed historical reconstruction of the theoretical derivation of this relationship by Eddington from 1924, see: Stefano Lecchini: How Dwarfs Became Giants. The Discovery of the Mass-Luminosity Relation . Bern Studies in the History and Philosophy of Science, 2007, ISBN 3-9522882-6-8 (English).
  24. Ben Zuckerman, Inseok Song, MS Bessell: The AB Doradus Moving Group . In: The Astrophysical Journal . 613, No. 1, 2005, pp. L65-L68. doi : 10.1086 / 425036 .
  25. Mini-Invasion of Exoplanets - Article in Telepolis , June 17, 2008
  26. Three super-earths around HD 40307 - article at astronews.com , June 16, 2008
  27. See e.g. B. Stability of planetary orbits in double stars. bibcode : 2002ESASP.518..547P
  28. M. Barber, F. Marzari, H. Scholl: formation of terrestrial planets in close binary systems: The case of α Centauri A . In: Astronomy & Astrophysics . tape 396 , December 2002, p. 219–224 , doi : 10.1051 / 0004-6361: 20021357 , arxiv : astro-ph / 0209118 .
This version was added to the list of articles worth reading on July 11, 2009 .