Vega

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Star
Wega (α Lyrae)
Position of Vega in the constellation Lyra
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation lyre
Right ascension 18 h 36 m 56.34 s
declination + 38 ° 47 ′ 1.3 ″
Apparent brightness +0.03 mag
Typing
B − V color index +0.00 
U − B color index −0.01 
R − I index −0.03 
Spectral class A0 V
Variable star type Delta Scuti star 
Astrometry
Radial velocity (−20.6 ± 0.2) km / s
parallax (130.23 ± 0.36)  mas
distance (25.0 ± 0.1)  ly
(7.68 ± 0.02)  pc  
Visual absolute brightness M vis +0.60 mag
Proper movement 
Rec. Share: (200.94 ± 0.32)  mas / a
Dec. portion: (286.23 ± 0.40)  mas / a
Physical Properties
Dimensions 2.20 ± 0.10  M ☉
radius 2.73 ± 0.01  R ☉
Luminosity

37 ± 3  L ☉

Effective temperature 7600 (equator) -
10000 (pole)  K
Metallicity [Fe / H] approx. −0.5 dex
Rotation time 12.5 h
Age (480 ± 95) 10 6  a
Other names
and catalog entries
Bayer name α Lyrae
Flamsteed name 3 lyre
Bonn survey BD + 38 ° 3238
Bright Star Catalog HR 7001 [1]
Henry Draper Catalog HD 172167 [2]
Gliese catalog FY 721 [3]
Hipparcos catalog HIP 91262 [4]
SAO catalog SAO 67174 [5]
Tycho catalog TYC 3105-2070-1 [6]
Other names • LTT 15486 • ADS 11510; FK5  699
annotation
Wega used to be the reference star for brightness and photometry.
  1. ↑ Calculated from apparent brightness and distance.

Wega , also Vega , or in the Bayer name α Lyrae , is the main star of the constellation Lyra (Lyra). The name is derived from the Arabic expressionالنسر الواقع, an-nasr al-wāqiʿ ab, which in translation means "descending (eagle)". The star is part of the great summer triangle and in white light the brightest star in the northern sky . With its magnitude of 0.0, it used to be used as a reference star for measuring brightness ( photometry ). Wega is, like the sun , in the local flake .

General

Wega is the brightest star in the constellation Lyra

Wega, together with the main stars of the constellations swan and eagle, forms the so-called summer triangle. It is the fifth brightest star in the night sky and the third brightest star in the northern hemisphere after Sirius and Arcturus . It is about 25 light-years from the Sun, making it a relatively nearby star. Along with Arktur and Sirius, Wega is one of the brightest stars in the vicinity of the sun.

Wega has been extensively studied by astronomers. This led to the fact that it is "probably the most important star after the sun". Due to the precession of the earth, Vega was the pole star about 14,000 years ago, and the Earth's axis will point back towards Vega in about 12,000 years. However, Vega will not come as close to the celestial pole as the current pole star α Ursae Minoris.

The great brightness of the Vega made Friedrich Wilhelm Struve suspect around 1835 that it was so close to the solar system that a distance determination would be possible. In 1838 he succeeded in measuring the tiny angular displacement of just 0.13 ″ and thus provided further evidence of the heliocentric worldview . Bessel at Stern 61 Cygni had predicted him a few months as the first evidence .

Wega served the astronomers as a zero point for calibrating the photometric brightness scale (see also pole sequence ). It was also one of the A0V stars that, due to their relatively constant intensity in the visual region of the spectrum, served as the zero point for the BV and UB color indices in the Johnson-Morgan UBV system .

Physical Properties

Absolute size comparison between the flattened Vega in equatorial view (left) and the sun (right).

Wega is a bluish-white main sequence star that, like all main sequence stars, fuses hydrogen to helium in its core. With an age between 386 and 572 million years, Wega is one of the even younger stars. It is relatively poor in “metals” (elements that have a higher atomic number than helium ). It is believed that Vega is a variable star that periodically changes very little in brightness. Wega has about 2.2 times the mass and 37 times the luminosity of the sun.

Hydrogen is fused to helium inside the star by the Bethe-Weizsäcker cycle (CNO cycle). This process requires a temperature of over 16 million K, which is higher than the core temperature of the sun. However, this nuclear fusion reaction is more efficient than the sun's proton / proton reaction . In the core is a convection zone, which merges into a radiation zone towards the outside. With the sun it's the other way round. There is the radiation zone on the inside and the convection zones follow towards the surface.

The visible spectrum is dominated by absorption lines of hydrogen, especially the lines of the Balmer series . The lines of the other elements are only weakly pronounced, those of magnesium, iron and chromium are most easily recognizable. Wega's X-ray radiation is very low. This indicates that the star's corona is very faint or does not exist at all.

Since stars with higher mass fuse their hydrogen much faster than stars with lower mass, the lifetime of Wega is correspondingly short at 1 billion years (corresponds to a little less than a tenth of the lifetime of the sun). With that she will soon have half of her main series time behind her. After that, it will expand into a red giant of spectral class M, only to end up as a white dwarf .

rotation

It used to be assumed that Vega was a slowly rotating star with a fairly constant surface temperature. According to Peterson's measurements, Vega rotates very quickly around its axis, which is inclined by 4.5 degrees to our observation line, and at 93% the speed that would tear the star apart.

Investigations with the CHARA interferometer at the Mount Wilson Observatory in California have shown that the Vega photosphere at the equator is 2400  K cooler than at the poles . The reason that the temperatures at the poles are 10,000 K and at the equator 7600 K is due to the bulge under the centrifugal force of the rapid rotation around the polar axis within 12.5 hours . At the equator there is a peripheral speed of 274 km / s, the pole diameter is 23% smaller than the equator diameter ( flattening  1: 4.35).

The temperature difference can be explained by the position of the polar region, which is much closer to the hot star interior. This effect is known as gravity darkening. From the earth you can see one of Vega's poles.

Frequency of elements

Astronomers refer to elements with an atomic number higher than that of helium as “metals”. The metallicity of Wega's photosphere with [M / H] = −0.5 is about 32% of the value of the sun's atmosphere. For comparison, Sirius has with [M / H] = +0.5 three times the occurrence of metals compared to the sun. The proportion of elements that are heavier than helium in the sun is approximately: Z sun  = 0.0172 ± 0.002. Vega therefore contains only about 0.54% heavier elements than helium.

Vega's unusually low metallicity makes it a weak lambda bootis star (a group of stars with low metallicity). However, the reason for the existence of such chemically unusual A0-F0 spectral class stars remains unclear. One possibility is the diffusion or the loss of matter of the stars. However, stellar models show that this would normally only occur at the end of the life of the hydrogen fusion phase. The star could also have originated from an interstellar cloud of gas or dust that was unusually poor in metals.

The observed ratio of helium to hydrogen vegas is 0.030 ± 0.005, which is about 40% lower than that of the sun. This could be caused by the disappearance of a helium convection zone near the surface. Instead, the energy is transported through a radiation zone, which could cause an anomaly in frequencies through diffusion.

Magnetic field

In 2009, French astronomers detected a magnetic field with the stellar spectropolarimeter NARVAL of the Bernard Lyot telescope. They found the so-called Zeeman effect in the star's spectrum . The spectral lines are split up by the influence of the magnetic field. The strength of Vega's magnetic field is around 50  micro-tesla, between that of the earth and that of the sun.

system

Measurements in the infrared range know that there is a build-up of matter around Vega. Wega was the first star (1983) to discover a disk of dust.

Increased infrared radiation

The infrared image (wavelength 24 µm) recorded by the Spitzer Space Telescope does not show the star itself, but the disk of dust that surrounds Wega. Their radius is at least 815  AU .

One of the first results of the Infrared Astronomical Satellite (IRAS) was the discovery of increased infrared radiation from Wega. This radiation came from an area with a radius of 10 ″ around the star. With the known distance of the star one comes to a radius of 80  AU . It is believed that this radiation comes from an area where particles of the order of 1 mm are floating. Smaller particles of matter would be removed by the radiation pressure or fall into the star by the Poynting-Robertson effect .

Dust disc

Due to the increased radiation in the infrared range, we know that Vega is surrounded by a disk of gas and dust. This dust is likely the result of collisions between objects in an orbiting disk of debris. This is similar to the Kuiper belt in the solar system.

In 2003, British astronomers calculated that the properties of this disk could probably best be explained by a planet resembling Neptune . This would make the Vega system possibly the star system that is most similar to the solar system . The center of Wega's life zone is 7.1  AU . A planet at this distance would have an orbital period of 10.9 years.

Stars that show excessive radiation due to the dust in the infrared region of the spectrum are also called "Vega-like" stars. Irregularities in Wega's dust disk could also indicate at least one planet that could be similar in size to Jupiter's orbiting Wega.

Possible planetary system

Despite an intensive search and many assumptions, no planet has yet been detected. However, a planetary system cannot be ruled out either.

Move

The apparent movement of Vega: the purple line shows the proper movement, the green curve line represents the actual movement in the sky (parallax from an angle perspective and proper movement superimposed).

Vega belongs to the Castor crowd . The stars in this cluster all have the same speed and come from a common origin. In addition to Wega, Castor , Fomalhaut , α Cephei (Alderamin) and α Librae (Zuben-el-dschenubi) are also members of this movement. They are all of a similar age.

Although Vega is currently only the fifth brightest star in the sky, it gets brighter over time due to its own motion, which runs in the direction of the sun. In about 210,000 years it will be the brightest star in the night sky and will remain so for about 270,000 years. The maximum apparent magnitude it will achieve will be −0.81 mag in 290,000 years.

history

Wega was the first star (apart from the Sun) to be photographed. In 1850, William Cranch Bond and John Adams Whipple made a daguerreotype of Vega on the large telescope of the Harvard College Observatory . It was also one of the first stars whose distances were determined using the parallax method and whose spectrum was also photographed.

Culture and literature

In the Chinese love story of the cowherd and the weaver , which is celebrated annually in China as Qixi and in Japan as Tanabata , Wega is the "star of the weaver" ( Chinese  織 女星  /  织 女星 , Pinyin Zhīnǚ Xīng , Japanese shokujo-sei or 織 姫星 , Orihime-boshi ), which is separated from the cowherd ( Altair ) by the “sky river” (Milky Way) .

In numerous titles, especially Eastern European science fiction , Vega is thematized as the longing destination of terrestrial space travelers or as the seat of extraterrestrial civilizations. The protagonist of the series of novels People Like Gods has a love affair with a being from a Vega world.

Invasion of the Vega (original title The Invaders) is a well-known American science fiction series of the 1960s / 70s.

In the first six episodes of the radio play series Commander Perkins from 1976-78, the eighth planet of Vega plays the main world of the series. The template is the Perry Rhodan series , in which Vega has a system of 42 planets, and which also saw Vega's eighth planet as a novel basis.

In the 16th episode of the Jan Tenner radio play series from 1984, Jan Tenner lands on the fifth planet of the Wega system and saves kidnapped children.

The male protagonist Adam Bates from the novel Adam and Lisa (1986) by Myron Levoy claims that he comes from the planet Vega X. It is his attempt to forget his bad childhood when he was mistreated with a chain by his father.

In 1997 filmed novel Contact by Carl Sagan is an encrypted radio signal containing the blueprint of a transport machine, received from the direction of Vega. The protagonist Eleanor "Ellie" Arroway, played by Jodie Foster in the film, travels to the Wega system with a machine built according to this plan.

There is a Celestial Rock Band from the USA, founded in March 2011, called Signals to Vega .

The Japanese card game Yu-gi-oh contains a card for Vega.

literature

Web links

Commons : Wega  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Hipparcos catalog (ESA 1997)
  2. ↑ a b c Bright Star Catalog
  3. ↑ Pulkovo radial velocities for 35493 HIP stars
  4. ↑ a b c Hipparcos, the New Reduction (van Leeuwen, 2007)
  5. ↑ a b c d e D. M. Peterson: "Vega is a rapidly rotating star" in Nature, March 20, 2006, arxiv : astro-ph / 0603520
  6. ↑ JP Aufdenberg, Mérand, A .; Coudé du Foresto, V .; Absil, O; Di Folco, E .; Kervella, P .; Ridgway, ST; Berger, DH; ten Brummelaar, TA; McAlister, HA; Sturmann, J .; Turner, NH: First Results from the CHARA Array. VII. Long-Baseline Interferometric Measurements of Vega Consistent with a Pole-On, Rapidly Rotating Star . In: The Astrophysical Journal . 645, 2006, pp. 664-675. arxiv : astro-ph / 0603327 . bibcode : 2006ApJ ... 645..664A . doi : 10.1086 / 504149 .
  7. ↑ T. Kinman: "The determination of T eff for metal-poor A-type stars using V and 2MASS J, H and K magnitudes" in "Astronomy and Astrophysics", September 2002, bibcode : 2002A & A ... 391.1039K .
  8. ↑ Austin F. Gulliver, Hill, Graham; Adelman, Saul J .: Vega: A rapidly rotating pole-on star . In: The Astrophysical Journal . 429, No. 2, 1994, pp. L81-L84. bibcode : 1994ApJ ... 429L..81G .
  9. ↑ T. Kinman, Castelli, F .: The determination of T eff for metal-poor A-type stars using V and 2MASS J, H and K magnitudes . In: Astronomy and Astrophysics . 391, 2002, pp. 1039-1052. bibcode : 2002A & A ... 391.1039K .
  10. ↑ Vasil'yev IA: On the Variability of Vega. Commission 27 of the IAU, March 17, 1989, accessed October 30, 2007 .
  11. ^ Matthew Browning, Brun, Allan Sacha; Toomre, Juri: Simulations of core convection in rotating A-type stars: Differential rotation and overshooting . In: Astrophysical Journal . 601, 2004, pp. 512-529. doi : 10.1086 / 380198 .
  12. ^ Thanu Padmanabhan: Theoretical Astrophysics . Cambridge University Press, 2002, ISBN 0-521-56241-4 .
  13. ↑ Kwong-Sang Cheng: Chapter 14: Birth of Stars. (No longer available online.) In: Nature of the Universe. Honk Kong Space Museum, 2007, archived from the original on April 23, 2012 ; Retrieved November 26, 2007 .
  14. ^ Michael Richmond: The Boltzmann Equation. Rochester Institute of Technology, accessed November 15, 2007 .
  15. ↑ Donald D. Clayton: Principles of Stellar Evolution and Nucleosynthesis . University of Chicago Press, 1983, ISBN 0-226-10953-4 .
  16. ^ E. Michelson: The near ultraviolet stellar spectra of alpha Lyrae and beta Orionis . In: Monthly Notices of the Royal Astronomical Society . 197, 1981, pp. 57-74. bibcode : 1981MNRAS.197 ... 57M .
  17. ↑ JHMM Schmitt: Coronae on solar-like stars. . In: Astronomy and Astrophysics . 318, 1999, pp. 215-230. bibcode : 1997A & A ... 318..215S .
  18. ↑ JG Mengel, Demarque, P .; Sweigart, AV; Gross, PG: Stellar evolution from the zero-age main sequence . In: Astrophysical Journal Supplement Series . 40, 1979, pp. 733-791. bibcode : 1979ApJS ... 40..733M .
  19. ↑ HM Antia, Basu, Sarbani: Determining solar abundances Using Helioseismology . In: The Astrophysical Journal . 644, No. 2, 2006, pp. 1292-1298. bibcode : 2006astro.ph..3001A .
  20. ↑ P. Renson, Faraggiana, R .; Boehm, C .: Catalog of Lambda Bootis Candidates . In: Bulletin d'Information Center Donnees Stellaires . 38, 1990, pp. 137-149. bibcode : 1990BICDS..38..137R . —Entry for HD 172167 on p. 144.
  21. ^ HM Qiu, Zhao, G .; Chen, YQ; Li, ZW: The Abundance Patterns of Sirius and Vega . In: The Astrophysical Journal . 548, No. 2, 2001, pp. 77-115. bibcode : 2001ApJ ... 548..953Q .
  22. ↑ Peter Martinez, Koen, C .; Handler, G .; Paunzen, E .: The pulsating lambda Bootis star HD 105759 . In: Monthly Notices of the Royal Astronomical Society . 301, No. 4, 1998, pp. 1099-1103. bibcode : 1998MNRAS.301.1099M .
  23. ↑ Saul J. Adelman, Gulliver, Austin F .: An elemental abundance analysis of the superficially normal A star VEGA . In: Astrophysical Journal, Part 1 . 348, 1990, pp. 712-717. bibcode : 1990ApJ ... 348..712A .
  24. ↑ Stefan Deiters: Wega has a magnetic field. astronews.com, June 24, 2009, accessed June 24, 2009 .
  25. ^ DA Harper, Loewenstein, RF; Davidson, JA: On the nature of the material surrounding VEGA . In: Astrophysical Journal, Part 1 . 285, 1984, pp. 808-812. bibcode : 1984ApJ ... 285..808H .
  26. ↑ KYL Su, Rieke, GH; Misselt, KA; Stansberry, YES; Moro-Martin, A .; Stapelfeldt, KR; Werner, MW; Trilling, DE; Bendo, GJ; Gordon, KD; Hines, DC; Wyatt, MC; Holland, WS; Marengo, M .; Megeath, ST; Fazio, GG: The Vega Debris Disk: A Surprise from Spitzer . In: The Astrophysical Journal . 628, 2005, pp. 487-500. arxiv : astro-ph / 0504086 . bibcode : 2005ApJ ... 628..487S . doi : 10.1086 / 430819 .
  27. ↑ Vega. Sol Company, accessed June 24, 2009 .
  28. ↑ Inseok Song, Weinberger, AJ; Becklin, EE; Zuckerman, B .; Chen, C .: M-Type Vega-like Stars . In: The Astronomical Journal . 124, No. 1, 2002, pp. 514-518. bibcode : 2002AJ .... 124..514S .
  29. ↑ D. Wilner, Holman, M .; Kuchner, M .; Ho, PTP: Structure in the Dusty Debris around Vega . In: The Astrophysical Journal . 569, 2002, pp. L115-L119. bibcode : 2002ApJ ... 569L.115W .
  30. ↑ M. Wyatt: Resonant Trapping of Planetesimals by Planet Migration: Debris Disk Clumps and Vega's Similarity to the Solar System . In: The Astrophysical Journal . 598, 2002, pp. 1321-1340. bibcode : 2003ApJ ... 598.1321W .
  31. ↑ Sky and Telescope, April 1998.