Mu Sagittarii

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μ Sagittarii
Template:Location mark
Location of μ Sgr(circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) +3.85[2]
Characteristics
μ Sgr A
Evolutionary stage Blue supergiant (Aa)
Spectral type B8Iap[3] + B1.5V[4]
U−B Template:Engvar −0.52[5]
B−V Template:Engvar +0.22[5]
Variable type EA + α Cyg[6]
μ Sgr B
Spectral type B9III[4]
U−B Template:Engvar −0.11[5]
B−V Template:Engvar −0.04[5]
μ Sgr C
U−B Template:Engvar −0.30[5]
B−V Template:Engvar +0.23[5]
μ Sgr D
Spectral type B2IV[7]
U−B Template:Engvar −0.57[5]
B−V Template:Engvar +0.11[5]
μ Sgr E
Spectral type B2.5V[7]
U−B Template:Engvar −0.67[5]
B−V Template:Engvar +0.04[5]
Astrometry
Parallax (π)0.6437±0.038 mas[8]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)A: −7.1[7]
B: −1.2[9]
D: −3.3[7]
E: −2.1[7]
Details
μ Sgr Aa
Mass23[10] Template:Solar mass
Radius115[11] Template:Solar radius
Luminosity180,000[11] Template:Solar luminosity
Surface gravity (log g)1.75[10] cgs
Temperature12,200[10] K
μ Sgr Ab
Mass9.8 - 15[12] Template:Solar mass
Radius12.2[12] Template:Solar radius
Surface gravity (log g)4.0[12] cgs
Temperature23,000[12] K
Metallicity [Fe/H] dex
Age10[7] Myr
μ Sgr B
Luminosity603[13] Template:Solar luminosity
Temperature18,200[13] K
μ Sgr D
MassScript error: No such module "val".[14] Template:Solar mass
RadiusScript error: No such module "val".[14] Template:Solar radius
LuminosityScript error: No such module "val".[14] Template:Solar luminosity
Surface gravity (log g)Script error: No such module "val".[14] cgs
TemperatureScript error: No such module "val".[14] K
Metallicity [Fe/H] dex
μ Sgr E
MassScript error: No such module "val".[8] Template:Solar mass
RadiusScript error: No such module "val".[8] Template:Solar radius
LuminosityScript error: No such module "val".[8] Template:Solar luminosity
Surface gravity (log g)Script error: No such module "val".[8] cgs
TemperatureScript error: No such module "val".[8] K
Metallicity [Fe/H]{{{metal_fe2}}} dex
Database references
SIMBADμ Sgr AB
μ Sgr D
μ Sgr E

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Mu Sagittarii (μ Sagittarii, abbreviated Mu Sgr, μ Sgr) is a multiple star system in the constellation of Sagittarius. The brightest component, a blue supergiant designated Mu Sagittarii Aa, is formally named Polis Template:IPAc-en.[15] The system is 5,000 light-years from the Sun and is part of the Sgr OB1 stellar association.

System

The components of the Mu Sagittarii system are designated 'A' through 'E', in order of their distance from the brightest, which is Mu Sagittarii A. 'A' is itself a spectroscopic binary with components designated Mu Sagittarii Aa and Ab. Of the five visible stars, component C is considered an optical double, not physically close to the other stars. Component D has also been listed as a purely optical double by some authors,[7] but others consider it to be part of a trapezium system of four gravitationally bound stars (plus an unseen companion).[9]

Component Apparent
Magnitude[5] 		Separation
from Mu Sagittarii A 		Minimum distance
from Mu Sagittarii A
A +3.88 - -
B +8.04 16.9 arcseconds 42 200 AU or 0.67 ly
C +10.99 25.8 arcseconds 64 500 AU or 1.02 ly
D +9.63 48.5 arcseconds 121 200 AU or 1.92 ly
E +9.25 50.0 arcseconds 125 000 AU or 1.98 ly

Nomenclature

μ Sagittarii (Latinised to Mu Sagittarii) is the system's Bayer designation. The designations of the five constituents as Mu Sagittarii A, B, C, D and E, and those of A's components - Mu Sagittarii Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[16]

The system occurs in the lunar station that was given the name πολις polis in a Coptic manuscript list of lunar stations, all of which Crum concluded were of Greek origin, in this case from polis "city".[17]

In 2016, the IAU organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[19] It approved the name Polis for the component Mu Sagittarii Aa on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[15]

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Dipper, refers to an asterism consisting of Mu Sagittarii, Phi Sagittarii, Lambda Sagittarii, Sigma Sagittarii, Tau Sagittarii and Zeta Sagittarii. Consequently, the Chinese name for Mu Sagittarii itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx.)[20]

Properties

Variability

Mu Sagittarii A varies in brightness and is classified as a variable star.[6] The two spectroscopic components eclipse each other with an orbital period of 181 days, causing a 0.08 magnitude drop in brightness (from +3.84 to +3.96).[12] In addition, it shows more irregular variations typical of an Alpha Cygni variable, irregularly pulsating hot supergiant stars.

Physical

Mu Sagittarii A appears as a type-B giant star with a total luminosity of 180,000 times that of the Sun and a radius of 115 times the Sun's. This means that Mu Sagittarii Aa's diameter is greater than that of the orbit of Mercury, or a little more than one astronomical unit (the average distance from Earth to the Sun). Its mass is 23 times the solar mass while it has a surface temperature of 11,100 K. Mu Sagittarii Aa is a type B8 blue supergiant and the companion (Mu Sagitarii Ab) is a type B2 giant. Its high mass means it has sufficient mass to end its life in a core-collapse supernova explosion.

The remaining components are very weakly bound to the Polis system, and although Mu Sagittarii is visible to the naked eye, the properties of the secondary components are highly uncertain.

The apparent magnitude for component B has been measured at between +8.04[5] and 10.481,[21] leading to uncertainties about its physical properties, distance, and membership of the system. The Washington Double Star Catalog gives a magnitude of 10.48 and the Catalog of Components of Double and Multiple Stars a magnitude of 11.5.[22][23]

Component D has an early B spectral type, near B3.[24] The full MK spectral type has been measured as B2 IV, and the assumption of a subgiant luminosity suggests that it is more distant than the other stars of the system.[7] The spectral type has also been estimated photometrically as B2 V, and a main sequence luminosity matches the distance of the other stars.[9] Components D and E are located about 5,100 light-years from Earth based on their Gaia Data Release 3 parallaxes.[14][8]

References

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  3. ↑ Script error: No such module "Citation/CS1".
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  5. ↑ a b c d e f g h i j k l Script error: No such module "Citation/CS1".
  6. ↑ a b Script error: No such module "Citation/CS1".
  7. ↑ a b c d e f g h Script error: No such module "Citation/CS1".
  8. ↑ a b c d e f g Template:Cite Gaia DR3 Gaia DR3 record for this source at VizieR.
  9. ↑ a b c Script error: No such module "Citation/CS1".
  10. ↑ a b c Script error: No such module "Citation/CS1".
  11. ↑ a b Script error: No such module "citation/CS1".
  12. ↑ a b c d e Script error: No such module "Citation/CS1".
  13. ↑ a b Script error: No such module "Citation/CS1".
  14. ↑ a b c d e f Template:Cite Gaia DR3 Gaia DR3 record for this source at VizieR.
  15. ↑ a b Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ See station 22 in footnote 12 in Stefan Weinstock, "Lunar Mansions and Early Calendars", Journal of Hellenic Studies, Volume 69, November 1949, pp. 48-69.
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ Script error: No such module "citation/CS1".
  20. ↑ Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日 Template:Webarchive
  21. ↑ Script error: No such module "Citation/CS1".
  22. ↑ Script error: No such module "Citation/CS1".
  23. ↑ Script error: No such module "Citation/CS1".
  24. ↑ Script error: No such module "Citation/CS1".

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External links

Template:Stars of Sagittarius

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