Zeta Sagittarius (ζ Sagittarius, Zeta Sagittarii, Sagittarii , abbreviated. Zeta Sgr, ζ Sgr ) is a multiple star system in the constellation Sagittarius .
Zeta Sagittarius; ξ Sagittarius | |||
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Double star | |||
Observational data ( Epoch J2000.0 ) | |||
Type of | Double star | ||
Right ascension | |||
Declination | |||
Distance | 88 ± 2 sv. years (27.0 ± 0.6 pc ) [a] | ||
Visible magnitude ( V ) | +2.59 [2] | ||
Constellation | Sagittarius | ||
Astrometry | |||
Radial velocity ( R v ) | 22 [3] km / s | ||
Proper motion (μ) | RA: +10.79 [1] mas per year Dec: +21.11 [1] mas per year | ||
Parallax (π) | 36.98 ± 0.87 [1] mas | ||
Absolute magnitude (V) | 0.42 [4] | ||
Specifications | |||
Spectral class | A2.5 Va [5] | ||
Color Indicator ( B - V ) | + 0.08 [2] | ||
Color Index ( U - B ) | +0.05 [2] | ||
physical characteristics | |||
Weight | (A + B) 5.26 ± 0.37 [6] M ☉ | ||
Age | ~ 500-710 million. [6] years | ||
Orbit elements | |||
Period ( P ) | 21.00 ± 0.01 [6] years | ||
Semi-axis ( a ) | 0.489 ± 0.001 [6] " | ||
Eccentricity ( e ) | 0,211 ± 0,001 [6] | ||
Inclination ( i ) | 111.1 ± 0.1 [6] ° v | ||
Node (Ω) | 74.0 ± 0.1 [6] ° | ||
Periastron Epoch ( T ) | 2005.99 ± 0.03 [6] | ||
Pericenter argument (ω) | 7.2 ± 0.6 [6] | ||
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Information in databases | |||
SIMBAD | data | ||
The star has 2 components Their parameters are presented below: | |||
Although the star has the designation Zeta (the 6th letter of the Greek alphabet ), the star itself is the 3rd in brightness in the constellation, after Epsilon Sagittarius (1.79 m ) and Sigma Sagittarius (+2.05 m ). The star has an apparent magnitude of +2.59 [2] , and, according to the Bortl scale , is visible to the naked eye even in the inner city sky ( eng. Inner-city ).
From the parallax measurements obtained during the Hipparcos mission [1] , it is known that the star is removed by about 88 ± 2 of sv. years ( 27.0 ± 0.6 pc ) from the Earth . The star is observed south of 61 ° c. sh. that is, that is, south of Aberdeen ( 57 ° N lat. ), Oslo ( 59 ° N lat. ), St. Petersburg ( 59 ° N lat. ). The Zeta Sagittarius star has a large southern declination and therefore, in the middle latitudes of Russia, the star is visible very low above the horizon. The best time to observe is July , when it is visible in the southern regions of Russia [8] .
Zeta Sagittarius moves at a speed 2 times faster relative to the Sun than other stars: its radial heliocentric speed: +22 km / s [8] [3] , which is 2.2 times faster than the speed of local stars of the Galactic disk , and also this means that the star is moving away from the Sun and about 1.0-1.4 million years ago, was within 7.5 ± 1.8 sv. years ( 2.3 ± 0.55 pc ) from the Sun [9] .
Content
Star Name
Zeta Sagittarius - ( Latinized version of the Latin. Zeta Sagittarii ) is the designation of Bayer , he gave the star in 1603 [4] .
The star also has the designation given by Flemsteed - 38 Sagittarius ( Latin 38 Sagittarii ) and the designation given by Gould - 130 G Sagittarius ( Latin 130 G Sagittarii ) [4] .
Zeta Sagittarius has the traditional name Askell ( Latin Ascella ), from the Late Latin word meaning “armpit” (Sagittarius). In the catalog of stars "Calendar Al-Ahsashi Al-Muakket" this star was labeled Talat al-Sadirah ( lat. Thalath al Sadirah ), which was translated into Latin as Tertia τού al Sadirah, which means "the third returning ostrich", since Fi Strelets , Sigma Strelets , Zeta Strelets, Hee Sagittarius , Tau Sagittarius form asterism in the “returning (to the nest) ostriches” [10] .
In 2016, the International Astronomical Union organized a Working Group under the IAU on Star Names (WGSN) [11] to catalog and standardize the names of proper stars . The WGSN approved the name Askella (“Ascella”) for the Zeta Strelets component A. From September 12, 2016, it is included in the List of Star Names approved by the MAS [12] .
Zeta Sagittarius, along with Gamma Sagittarius , Delta Sagittarius , Epsilon Sagittarius , Lambda Sagittarius , Sigma Sagittarius , Tau Sagittarius and Fi Sagittarius form Asterism Kettle [13] .
In Chinese astronomy The star belongs to the constellation 參 參 ( Sān Qí ) "Bucket" together with Fi Sagittarius , Lambda Sagittarius , Mu Sagittarius , Sigma Sagittarius , Tau Sagittarius . Consequently, the Chinese name of the Zeta Sagittarius itself is 斗 宿 一 , ( Dǒu Sù yī - “First Star of the Bucket” - English of the First Star of Dipper [14] .
At the moment the star is resolved into three components by various methods. When naming the three components, the Zeta Sagittarius A, B, and C designations are used according to the convention used by the Washington Catalog of Visual Binary Stars (WDS) and adopted by the International Astronomical Union (MAS) to refer to star systems .
Multiple system properties
Zeta Strelets has two main gravitationally related components: the first component, A, is a star of spectral class A with an apparent magnitude of +3.26 m . The second component, B, has an apparent magnitude of +3.47 m (the total brightness gives the binary a magnitude of +2.61 m , which we observe). Both components are classified either as dwarfs of the A2 spectral class (which implies a thermonuclear reaction of helium synthesis from hydrogen ), or as A4 subgiants (which implies a recent halt of the synthesis), the last statement seems to be the most correct [7] .
At a distance of 71.6 " there is another star, component C of the eleventh magnitude (10.63 m ), but most likely it is an optical component and is not gravitationally connected with the other two components.
Due to their proximity to each other, the parameters of stars are poorly understood (the light of one star distorts the light of another). They revolve around each other at an angular distance on average of at least half a second arc [6] (which makes their resolution a big problem even for an eye armed with a telescope ). At a distance of 88 ± 2 sv. years this corresponds to the size of the major semiaxis 13.4 AU. (40% further than Saturn's orbit). The rotation period of the system is at least 21.075 years . The orbit has a moderate eccentricity equal to 0.211 [6] (approximately as in Mercury - 0.205). The stars approach at a minimum distance of 10.6 AU. (that is, approximately into the orbit of Saturn ), and removed them to a maximum distance of 16.1 AU. (that is, about 15% closer than the orbit of Uranus ) [7] . From the orbit and Kepler's laws, one can find the mass function , which corresponds to the lower estimate of the total mass of the system of 5.26 ± 0.37 [6] , which is 25% more than is determined by luminosity and temperature (and the theory of stellar structure and evolution) [7] .
In order for a planet similar to our Earth to receive about as much energy as it receives from the Sun, it would have to be placed at a distance of 5.57 AU. that is, about where Jupiter is located in the Solar System . Moreover, from such a distance, Zeta Sagittarius A would look almost 40% smaller than our Sun , as we see it from the Earth - 0.31 ° [b] (the angular diameter of our Sun is 0.5 °). However, the system is unlikely to have not only habitable planets, but also planets in general, since the joint gravity of both stars will sweep them out of the system. The age of the Zeta Strelets system is about 0.5–0.7 billion years [6] , so if any planets are formed in it, then most likely they will be similar to Mercury or Venus in the Solar System , as in the distance to a star, and by its properties. [7] .
Component A
Zeta Sagittarius A is a dwarf , A2V spectral class , which indicates that the hydrogen in the core of the star serves as a nuclear "fuel," that is, the star is on the main sequence . The star radiates energy from its outer atmosphere at an effective temperature of about 9000 K [7] , which gives it the characteristic white-yellow color of a star of spectral class A and makes it a source of ultraviolet radiation [c] .
The mass of a star is usual for a dwarf and is: 2.2 [7] . Its radius is more than three times the radius of the sun and is 3.27 [4] . Also, the star is much brighter than our Sun , its luminosity is 31 [7] .
The star has a surface gravity of 3.9 CGS [15] or 79.4 m / s 2 , that is, significantly less than on the Sun ( 274.0 m / s 2 ), which, apparently, can be explained by the large surface of the star. The rotation speed is equal to 77 km / s [16] , which gives a period of rotation of the star about 5 days.
Component B
Zeta Strelets B is a star of spectral class A4 [7] . The mass of the star is 2.1 [7] . This star, like its companion, is much brighter than our Sun , its luminosity is 26 [7] . The star radiates energy from its outer atmosphere at an effective temperature of about 8500 K [7] , which gives it the characteristic white-yellow color of a star of spectral class A and makes it, like its companion, a source of ultraviolet radiation .
History of studying the multiplicity of a star
According to the Washington catalog of visual binary stars , the parameters of these components are listed in the table [17] [18] :
Component | Year | Number of measurements | Position angle | Angular distance | Visible magnitude 1 component | Visible magnitude 2 component |
---|---|---|---|---|---|---|
AB | 1867 | lot | 258 ° | 0.9 | 3.27 m | 3.48 m |
2017 | 247 ° | 0.6 | ||||
AB-С | 1905 | 2+ | 262 ° | 75.0 | 2.6 m | 10.63 m |
1977 | 302 ° | 74.6 | ||||
2013 | 302 ° | 71.6 |
Summarizing all the information about the star, we can say that the star has a satellite - Zeta Sagittarius B and that the stars move together in space, that is, the stars are not just on the line of sight, but are connected to each other gravitationally.
At a distance of 71.6 " is the star of the eleventh magnitude (10.63 m ), that is, component" C " [19] . If it is really part of the system, then it must be an orange dwarf of spectral class K7 located at a distance of at least 2000 a from a pair of stars AB, which rotates with a period of at least 40,000 years . However, small shifts in angular distance over the past century are associated with the expected motion of a pair of stars AB in space relative to the distant background, and therefore small movements of the Is probably a coincidence of stars line-of-sight lines, adding uncertainty to the Zeta Strelets system [7] .
Notes
Comments
- ↑ Distance calculated by the given value of parallax
- ↑ Angular diameter (δ) is calculated by the formula:
- where D S is the diameter of a star, expressed in a.e. ; d CZ - distance to habitable zone
- ↑ According to the law of Wien displacement , the radiation energy of an absolutely black body is maximum at a given temperature at a wavelength λ b = (2.898⋅10 6 nm • K) / (6813 K) ≈ 322 nm , which lies in the near ultraviolet part of the electromagnetic spectrum
Sources
- ↑ 1 2 3 4 5 6 (Eng.) Van Leeuwen, F. ( November 2007 ), " Validation of the new Hipparcos reduction ", Astronomy and Astrophysics T. 474 (2): 653–664 , DOI 10.1051 / 0004-6361 : 20078357
- ↑ 1 2 3 4 Johnson, HL; Iriarte, B .; Mitchell, RI; Wisniewskj, WZ UBVRIJKL photometry of the bright stars (Eng.) // Communications of the Lunar and Planetary Laboratory : journal. - 1966. - Vol. 4 , no. 99 - .
- 2 1 2 Wilson, RE General Catalog of Stellar Radial Velocities: [ eng ] . - Carnegie Institute of Washington DC , 1953 .
- ↑ 1 2 3 4 5 Ascella (Zeta Sagittarii, 38 Sagittarii) Star Facts (English) . Universe Guide .
- ↑ 1 2 (English) * zet Sgr - Double or multiple star , Center de Données astronomiques de Strasbourg , < http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Zeta+Sagittarii > . Checked June 27, 2019.
- ↑ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 (eng.) De Rosa, Robert J .; Patience, Jenny; Vigan, Arthur & Wilson, Paul A. ( 2011 ), “ The VAST Survey - II. Orbital Motion Monitoring of A-type Star Multiples ”, Monthly Notice of the Royal Astronomical Society , Vol. T. 422: 2765–2785 , DOI 10.1111 / j.1365-2966.2011.20397.x
- ↑ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ASCELLA (Zeta Sagittarii) (Eng.) . Jim Kaler, Stars .
- ↑ 1 2 HR 7194 . Catalog of bright stars .
- ↑ (Eng.) Dybczyński, PA ( April 2006 ), " Simulating observable comets. III. Real stellar perturbers of the cloud and their output ", Astronomy and Astrophysics T. 449 (3): 1233–1242 , DOI 10.1051 / 0004 -6361: 20054284
- Ob Knobel, EB Al Achsasi Al Mouakket, Mohammad Al Achsasi Al Mouakket (Eng.) // Monthly Notices of the Royal Astronomical Society : journal. - Oxford University Press , 1895. - June ( vol. 55 ). - P. 430 . - DOI : 10.1093 / mnras / 55.8.429 . - .
- ↑ IAU Working Group on Star Names (WGSN) (English) . The appeal date is May 22, 2016.
- ↑ Naming Stars (eng.) . IAU.org . The appeal date is December 16, 2017.
- ↑ Teapot (English) . constellation-guide.com. The appeal date is May 13, 2017.
- К (whale.) AEEA (Activities of Exhibition and Education in Astronomy) 天文 資訊 網 2006 年 7 月 8
- ↑ (Eng.) Gray, RO; Corbally, CJ; Garrison, RF & McFadden, MT ( October 2003 ), " Controversy to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I. ", The Astronomical Journal T. 126 (4) : 2048–2059 , DOI 10.1086 / 378365
- ↑ (Eng.) Royer, F .; Zorec, J. & Gómez, AE ( February 2007 ), " Rotational velocities of A-type stars. III. Velocity distributions ", Astronomy and Astrophysics T. 463 (2): 671–682 , DOI 10.1051 / 0004-6361: 20065224
- ↑ Ascella (English) . Alcyone Bright Star Catalog .
- ↑ Vizier catalog entry (English) .
- ↑ (English) GSC 06885-02777 - Star , Center de Données astronomiques de Strasbourg , < http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%402477635&Name=GSC%2006885-02777 > . Checked June 27, 2019.