Akrab
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Double star Akrab |
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| AladinLite | |||||||||||||||||||||||||||||||||||
| Constellation | Scorpio | ||||||||||||||||||||||||||||||||||
| Apparent brightness | 2.50 mag | ||||||||||||||||||||||||||||||||||
| Astrometry | |||||||||||||||||||||||||||||||||||
| Radial velocity | −1 ± 2 km / s | ||||||||||||||||||||||||||||||||||
| parallax | 7.0 ± 0.1 mas | ||||||||||||||||||||||||||||||||||
| distance | 466 ± 7 ly (143 ± 3 pc ) |
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| Proper movement : | |||||||||||||||||||||||||||||||||||
| Rec. Share: | β 1 : −5.20 ± 0.92 mas / a | ||||||||||||||||||||||||||||||||||
| Dec. portion: | β 1 : −24.04 ± 0.64 mas / a | ||||||||||||||||||||||||||||||||||
| orbit | |||||||||||||||||||||||||||||||||||
| period | 12,800 a | ||||||||||||||||||||||||||||||||||
| Individual data | |||||||||||||||||||||||||||||||||||
| Names | β 1 ; β 2 | ||||||||||||||||||||||||||||||||||
| Observation data: | |||||||||||||||||||||||||||||||||||
| Right ascension | β 1 | 16 h 05 m 26.23 s | |||||||||||||||||||||||||||||||||
| β 2 | 16 h 05 m 26.57 s | ||||||||||||||||||||||||||||||||||
| declination | β 1 | −19 ° 48 ′ 19.6 ″ | |||||||||||||||||||||||||||||||||
| β 2 | −19 ° 48 ′ 06.9 ″ | ||||||||||||||||||||||||||||||||||
| Apparent brightness | β 1 | 2.62 likes | |||||||||||||||||||||||||||||||||
| β 2 | 4.92 mag | ||||||||||||||||||||||||||||||||||
| Typing: | |||||||||||||||||||||||||||||||||||
| Spectral class | β 1 | B1 V | |||||||||||||||||||||||||||||||||
| β 2 | B2 V | ||||||||||||||||||||||||||||||||||
| B − V color index | β 1 | −0.07 | |||||||||||||||||||||||||||||||||
| β 2 | −0.02 | ||||||||||||||||||||||||||||||||||
| U − B color index | β 1 | −0.87 | |||||||||||||||||||||||||||||||||
| β 2 | −0.70 | ||||||||||||||||||||||||||||||||||
| Physical Properties: | |||||||||||||||||||||||||||||||||||
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Absolute vis. Brightness M vis |
β 1 | −3.2 / −2.6 /? like | |||||||||||||||||||||||||||||||||
| β 2 | −1.8 / 0.2 /? like | ||||||||||||||||||||||||||||||||||
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Absolute bol. Brightness M bol |
β 1 | −6.6 / −5.1 /? like | |||||||||||||||||||||||||||||||||
| β 2 | −4.1 / −0.6 /? like | ||||||||||||||||||||||||||||||||||
| Dimensions | β 1 | 15.0 / 10.4 / 8 M ☉ | |||||||||||||||||||||||||||||||||
| β 2 | 8.2 / 3.5 /? M ☉ | ||||||||||||||||||||||||||||||||||
| radius | β 1 | 6.3 / 4.0 /? R ☉ | |||||||||||||||||||||||||||||||||
| β 2 | 2.9 / 2.4 /? R ☉ | ||||||||||||||||||||||||||||||||||
| Luminosity | β 1 | 30,000 / 8,000 /? L ☉ | |||||||||||||||||||||||||||||||||
| β 2 | 3,200 / 125 /? L ☉ | ||||||||||||||||||||||||||||||||||
| Effective temperature | β 1 | 28,000 / 26,400 /? K | |||||||||||||||||||||||||||||||||
| β 2 | 24,000 / 13,000 /? K | ||||||||||||||||||||||||||||||||||
| Age | 6.3 ± 3.0 bill. A | ||||||||||||||||||||||||||||||||||
| Other names and catalog entries |
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| Values separated by a slash are listed in the order Aa / Ab / B (line β 1 ) and C / Ea / Eb (line β 2 ). Absolute and bolometric magnitudes have been adjusted for interstellar absorbance . | |||||||||||||||||||||||||||||||||||
Akrab ( Arabic العقرب, DMG al-ʿaqrab 'the Scorpion'), also called Graffias or after Bayer β Scorpii ( Beta Scorpii , β Sco for short), is a star in the constellation Scorpio . With an apparent magnitude of 2.5 m , Akrab is the seventh brightest star in Scorpio.
It is a six-fold star system about 470 light years away, consisting of two triple systems, namely β 1 Scorpii and β 2 Scorpii . The components β 1 and β 2 Scorpii can already be separated into two stars by amateur astronomers with a telescope or telescope with an objective aperture of at least 5 cm. The resolution into further single stars is reserved for professional astronomy, as these are too close together for amateur instruments.
The Akrab system is a member of the Upper Scorpius Group, a subgroup of the Scorpius-Centaurus Association .
Structure and physical properties
β 1 and β 2 Scorpii appear as blue-white shining stars with apparent brightnesses and spectral classes of 2.62 m and B1 (β 1 ) as well as 4.92 m and B2 (β 2 ). The mutual angular distance is 13.7 ″, the position angle of the weaker component to the main star is 20 ° (as of 2017). An orbital movement can hardly be seen. The first guaranteed measurement was made by Wilhelm Herschel in 1779, where he measured a position angle of 25 °. Thus, β 2 Scorpii has moved only 5 ° around β 1 Scorpii within 238 years . The mutual orbital period is estimated to be 12,800 years.
β 1 Scorpii
β 1 Scorpii consists of stars β Scorpii A - which in turn twice and from the stars β Scorpii Aa and β Scorpii From there - and the star β Scorpii B .
β Scorpii A and B are 2.7 m and 5.9 m bright and 0.3 ″ apart, the position angle of component B with respect to A is 211 ° (as of 2017). The (double) star β Scorpii A and the (single) star β Scorpii B orbit each other with an orbital period of 610 years on a highly eccentric orbit ( e ≈ 0.9). However, the accuracy of the path elements is insufficient and the actual orbit time could still deviate significantly from this value (so far, the observation data only cover around a third of the calculated path). Further observations are necessary to refine the data on the orbit.
Β Scorpii Aa and Ab are two massive, hot stars that form a spectroscopic double star of type SB2 with an anomalous orbital period of 6.83 days (SB2 means that the lines of both components can be seen in the spectrum ). Their angular distance always is around a thousandth of a second of arc (distance and position angle by B 2018.0: 0.0007 "and 272.3 °; by B2019,0: 0.0013" and 90.0 °). β Scorpii Aa has 15.0 ± 0.7 solar masses , 6.3 ± 0.5 solar radii , an effective surface temperature of 28,000 ± 2,000 K and about 30,000 times the luminosity of the sun , the partner star β Scorpii Ab 10.4 ± 0.5 solar masses, 4.0 ± 0.3 solar radii, 26,400 ± 2,000 K effective surface temperature and around 8,000 solar luminosities. The spectral and luminosity classes of the individual stars cannot be clearly measured, but they are estimated at B0.5 IV to V for β Scorpii Aa and B1.5 V for β Scorpii Ab.
The mass of β Scorpii B is estimated to be 8 solar masses. A study from 1975 came to the conclusion that β Scorpii B may also be a binary star. A close companion star has not yet been confirmed. Should this still exist, then β 1 Scorpii would be a four-fold and Akrab a total of seven-fold star system.
β 2 Scorpii
β 2 Scorpii consists of the stars β Scorpii C and β Scorpii E , whereby β Scorpii E is again double and is composed of the stars β Scorpii Ea and β Scorpii Eb .
The apparent brightnesses for β Scorpii C and E are 5.1 m and 7.2 m , the distance and the position angle of the weaker component to the lighter one are 0.1 ″ and 22 ° (as of 2017). The stars need 39 years to orbit one another. As with β 1 Scorpii, there are open questions about the orbit. The total mass of the β 2 Scorpii system derived from the spectrum is 18.6 solar masses. If, however, the total mass is calculated from the orbital data, this results in only 2.9 ± 1.3 solar masses using the Hipparcos parallax (0.00819 ± 0.00117 ″). Only the use of a parallax of 0.0044 "would lead to a coherent result, but this would contradict the dynamic parallax of 0.0070" and the Hipparcos parallax, which coincide quite well. A study from 2014 therefore suggests a new investigation of the railway.
β Scorpii C is a main sequence star of spectral class B2 and luminosity class V. Based on its spectrum, its mass became 8.2 ± 0.4 solar masses, its radius 2.9 ± 0.5 solar radii, its effective surface temperature 24,000 ± 500 K and its luminosity determined to be 3,200 times that of the sun.
The subsystem β Scorpii E is a spectroscopic double star of the type SB1 (SB1 means that the lines of only one component can be seen in the spectrum). Its duplicity was - although suspected for a long time - only clearly proven in 2010. The first determination of the orbital period was 10.89 days; more recent studies from 2014 corrected this value to 11.08 days. β Scorpii Ea belongs to the spectral class B8pMn and has 3.5 ± 0.2 solar masses, 2.4 ± 0.1 solar radii, an effective surface temperature of 13,000 ± 800 K and 125 times the solar luminosity. Spectroscopic measurements also show that β Scorpii Ea is probably a mercury-manganese star ( see also: Pecular star ). Nothing is known about the properties of the component Eb because its spectrum cannot be observed.
β Scorpii D
When naming it, it is noticeable that the star system has no component D. This is related to the sequence of discovery of the individual stars and their subsequent renumbering according to an IAU guideline. In fact, the Washington Double Star Catalog records a component D - this means the 7.5 m bright star HD 144273. The distance and position angle to β 1 Scorpii are 519.2 ″ and 30 °. HD 144273 does not belong to the Akrab system, but only forms an optical double star with it . Like Akrab, HD 144273 is part of the Scorpius-Centaurus association and therefore has a similar proper movement.
Orbital elements and ephemeris
The track elements of the individual systems are as follows:
| Track element | β 1 Scorpii | β 2 Scorpii | ||
|---|---|---|---|---|
| Main system (A - B) |
Subsystem (Aa - Ab) |
Main system (C - E) |
Subsystem (Ea - Eb) |
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| Period of circulation | 610 a | 6.828245 ± 0.000009 d | 39.0 ± 2.9 a | 11.07666 ± 0.00030 d |
| Major semi-axis | 3.9 ″ (approx. 560 AU ) |
0.00142 ± 0.00002 ″ (approx. 0.2 AU) |
0.1328 ± 0.0060 ″ (approx. 19 AU) |
indefinite |
| Orbit inclination | 87.12 ° | 111.8 ± 0.7 ° | 41.1 ± 9.0 ° | indefinite |
| Argument of the node | 89.5 ° | 294.2 ± 0.8 ° | 184.0 ± 14.0 ° | indefinite |
| Epoch of the periastron | Year 2480 | JD 2,449,788.509 ± 0.019 | Year 2034.2 ± 9.9 | Heliocentric JD 2,455,449.17 ± 0.02 |
| eccentricity | 0.9093 | 0.291 ± 0.006 | 0.029 ± 0.057 | 0.078 ± 0.010 |
| Argument of the periapsis | 283 ° | 54.8 ± 1.3 ° | 350.0 ± 111.0 ° | 91.7 ± 4.8 ° |
(The conversion of the semi-major axes from arc seconds to AU was based on a parallax of 0.0070 ″.)
The following ephemeris can be calculated from these orbital elements (in each case mid-year):
| year | System A - B | System C - E | ||
|---|---|---|---|---|
| distance | Position angle | distance | Position angle | |
| 2018 | 0.32 ″ | 198.3 ° | 0.13 ″ | 21.9 ° |
| 2020 | 0.33 ″ | 201.8 ° | 0.12 ″ | 37.2 ° |
| 2025 | 0.36 ″ | 209.6 ° | 0.10 ″ | 89.2 ° |
| 2030 | 0.40 ″ | 216.2 ° | 0.11 ″ | 146.0 ° |
| 2050 | 0.56 ″ | 233.3 ° | 0.12 ″ | 333.6 ° |
| 2100 | 1.04 ″ | 249.5 ° | 0.11 ″ | 55.3 ° |
Coverings by the moon and planets
As a star near the ecliptic, Akrab can be covered by the moon and very rarely by planets. Coverings by planets occurred on December 9, 1802 by Mercury , on February 28, 1876 by Jupiter , on December 9, 1906 by Venus and finally on 13/14. May 1971 by Jupiter and its moon Io .
The covering by Jupiter and Io on 13./14. May 1971 was of great interest for the investigation of Akrab. While Jupiter covered the components β 1 and β 2 Scorpii, Io only covered β 2 Scorpii. The occultation was observed from observatories in Australia, India and South Africa. The central passage would have been observable roughly over the middle of the Indian Ocean . The entry and exit of β 2 Scorpii took place - depending on the location, deviating a few minutes - at around 5.45 p.m. UT and around 8.15 p.m. UT (for component β 1 , entry occurred later and exit earlier). The occlusion of β 2 Scorpii by Io was only observable from a relatively small part of the earth ( Caribbean and Florida ) because of the small angular diameter of the moon . At the observatory on St. Thomas ( Virgin Islands ), entry was on May 14, 1971 at 01: 59: 03.40 UT (± 0.08 s) and exit at 02: 03: 56.77 UT (± 0 , 04 s). Thus the coverage lasted only 293.39 ± 0.03 s. Overall, the coverage from 13./14. May 1971 valuable photometric and astrometric data were obtained, which allowed conclusions to be drawn about the physical properties of the stars. In addition, the binary star nature of β Scorpii C was discovered and the angular distance to the newly discovered component E was determined to be 0.097 ± 0.002 ″. Conversely, Jupiter and Io could also be studied. The cover provided new information about Jupiter's atmosphere and Io's diameter was determined to be 3,658 ± 6 km.
From 1975 to 1976 there was a series of occultations by the moon, during which Akrab was covered a total of 19 times.
See also
Web links
- Database links to SIMBAD :
- http://stars.astro.illinois.edu/sow/graffias.html
Individual evidence
- ^ Alan William James Cousins, Richard Hugh Stoy: Photoelectric magnitudes and colors of Southern stars . In: Royal Observatory Bulletin . Vol. 64. bibcode : 1962RGOB ... 64..103C . Quoted from SIMBAD .
- ↑ George A. Gontcharov: Vizier Online Data Catalog: Pulkovo radial velocities for 35493 HIP stars (Gontcharov, 2006) . In: VizieR On-line Data Catalog: III / 252. Originally published in: 2006PAZh ... 32..844G; 2006AstL ... 32..759G . 2007. bibcode : 2007yCat.3252 .... 0G . Catalog entry on VizieR.
- ↑ a b c d e David Holmgren et al. : Search for forced oscillations in binaries. II. Β Scorpii A. New physical parameters and a search for line profile variability . In: Astronomy and Astrophysics . Vol. 322, 1997, pp. 565-575. bibcode : 1997A & A ... 322..565H .
- ↑ a b c d e f g h María Eugenia Veramendi, Jorge Federico González: Spectroscopic study of early-type multiple stellar systems. I. Orbits of spectroscopic binary subsystems . In: Astronomy and Astrophysics . Vol. 563, 2014, Article ID A138, pp. 3, 5, 9-11. bibcode : 2014A & A ... 563A.138V , doi: 10.1051 / 0004-6361 / 201322840 .
- ↑ a b c d e f Dorrit Hoffleit, Wayne H. Warren Jr .: VizieR Online Data Catalog: Bright Star Catalog, 5th Revised Ed. (Hoffleit +, 1991) . In: VizieR On-line Data Catalog: V / 50. Originally published in: 1964BS .... C ...... 0H . 1995. bibcode : 1995yCat.5050 .... 0H . Catalog entries for β 1 Scorpii and β 2 Scorpii on VizieR .
- ^ Floor van Leeuwen: VizieR Online Data Catalog: Hipparcos, the New Reduction (van Leeuwen, 2007) . In: VizieR On-line Data Catalog: I / 311. Originally published in: 2007A & A ... 474..653V . 2008. bibcode : 2008yCat.1311 .... 0V . Catalog entry on VizieR.
- ↑ a b c d e f g h i j k l m n o p Gianni Catanzaro: First spectroscopic analysis of β Scorpii C and β Scorpii E. Discovery of a new HgMn star in the multiple system β Scorpii . In: Astronomy and Astrophysics . Vol. 509, 2010, Article ID A21. bibcode : 2010A & A ... 509A..21C , doi: 10.1051 / 0004-6361 / 200913332 .
- ↑ a b c d Thomas C. Van Flandern, Peter Espenschied: Lunar occultations of Beta Scorpii in 1975 and 1976 . In: The Astronomical Journal . Vol. 200, 1975, pp. 61-67. bibcode : 1975ApJ ... 200 ... 61V , doi: 10.1086 / 153760 .
- ^ Maria Antonietta Giannuzzi: The multiple system β Sco and the age of the Upper Scorpius complex . In: Astronomy and Astrophysics . Vol. 125, 1983, p. 302. bibcode : 1983A & A ... 125..302G .
- ↑ a b c d e f Brian D. Mason et al. : VizieR Online Data Catalog: The Washington Visual Double Star Catalog (Mason + 2001-2014) . Version 2018-06-11. In: VizieR On-line Data Catalog: B / wds. Originally published in: 2001AJ .... 122.3466M . 2018. bibcode : 2018yCat .... 102026M . Catalog entry on VizieR.
- ↑ a b David S. Evans et al. : Occultation study of the multiple star β Scorpii . In: The Astronomical Journal . Vol. 82, 1977, p. 502. bibcode : 1977AJ ..... 82..495E , doi: 10.1086 / 112080 .
- ^ A b David S. Evans, James L. Elliot, Deane M. Peterson: Occultation astrometry of the Beta Scorpii system . In: The Astronomical Journal . Vol. 83, 1978, p. 441. bibcode : 1978AJ ..... 83..438E , doi: 10.1086 / 112219 .
- ^ A b Diana M. Seymour et al. : Binary star orbits. II. Preliminary first orbits for 117 systems . In: The Astronomical Journal . Vol. 123, Ed. 2, 2002, pp. 1.029, 1.035, 1.037. bibcode : 2002AJ .... 123.1023S , doi: 10.1086 / 338441 . Catalog entry on VizieR.
- ↑ a b c d e Brian D. Mason, William I. Hartkopf, Andrei Tokovinin: Binary star orbits. IV. Orbits of 18 southern interferometric pairs . In: The Astronomical Journal . Vol. 140, Ed. 3, 2010, pp. 736-737, 739, 741-742. bibcode : 2010AJ .... 140..735M , doi: 10.1088 / 0004-6256 / 140/3/735 .
- ↑ a b Calculated with the Binary Star Calculator (Vers. 3) by Brian Workman according to the path elements listed in the table.
- ^ Ronnie Hoogerwerf: VizieR Online Data Catalog: OB association members in ACT + TRC Catalogs (Hoogerwerf, 2000) . In: VizieR On-line Data Catalog: J / MNRAS / 313/43. Originally published in: 2000MNRAS.313 ... 43H . 2000. bibcode : 2000yCat..83130043H . Catalog entry on VizieR.
- ↑ William B. Hubbard et al. : The Occultation of Beta Scorpii by Jupiter and Io. I. Jupiter . In: The Astronomical Journal . Vol. 77, Ed. 1, 1972, pp. 41-59. bibcode : 1972AJ ..... 77 ... 41H .
- ^ Paul Bartholdi, Frazer Owen: The Occultation of Beta Scorpii by Jupiter and Io. II. Io . In: The Astronomical Journal . Vol. 77, Ed. 1, 1972, pp. 60-65. bibcode : 1972AJ ..... 77 ... 60B .
- ^ William B. Hubbard, Thomas C. Van Flandern: The Occultation of Beta Scorpii by Jupiter and Io. III. Astrometry . In: The Astronomical Journal . Vol. 77, Ed. 1, 1972, pp. 65-75. bibcode : 1972AJ ..... 77 ... 65H .