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 /ˈpɒlɪs/.[13] The system is 5,000 light-years from the Sun and is part of the Sgr OB1 stellar association.
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 13m 45.8s[1] |
| Declination | −21° 03′ 32″[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 color index | −0.52[5] |
| B−V color index | +0.22[5] |
| Variable type | EA + α Cyg[6] |
| μ Sgr B | |
| Spectral type | B9III[4] |
| U−B color index | −0.11[5] |
| B−V color index | −0.04[5] |
| μ Sgr C | |
| U−B color index | −0.30[5] |
| B−V color index | +0.23[5] |
| μ Sgr D | |
| Spectral type | B2IV[7] |
| U−B color index | −0.57[5] |
| B−V color index | +0.11[5] |
| μ Sgr E | |
| Spectral type | B2.5V[7] |
| U−B color index | −0.67[5] |
| B−V color index | +0.04[5] |
| Astrometry | |
| Parallax (π) | 0.6437 ± 0.038 mas[8] |
| Distance | 5,100 ± 300 ly (1,550 ± 90 pc) |
| Absolute magnitude (MV) | A: −7.1[7] B: −1.2[9] D: −3.3[7] E: −2.1[7] |
| Details | |
| μ Sgr Aa | |
| Mass | 14.1 – 30,[10] 23[11] M☉ |
| Radius | 115[11] R☉ |
| Luminosity | 180,000[11] L☉ |
| Surface gravity (log g) | 2.0[10] cgs |
| Temperature | 12,000[10] K |
| μ Sgr Ab | |
| Mass | 9.8 - 15[10] M☉ |
| Radius | 12.2[10] R☉ |
| Surface gravity (log g) | 4.0[10] cgs |
| Temperature | 23,000[10] K |
| Age | 10[7] Myr |
| μ Sgr B | |
| Luminosity | 603[12] L☉ |
| Temperature | 18,200[12] K |
| μ Sgr D | |
| Luminosity | 1,660[12] L☉ |
| Temperature | 20,400[12] K |
| μ Sgr E | |
| Mass | 6.47±0.21[8] M☉ |
| Radius | 6.36+0.36 −0.31[8] R☉ |
| Luminosity | 2,668+337 −298[8] L☉ |
| Surface gravity (log g) | 3.55±0.03[8] cgs |
| Temperature | 16,700+200 −300[8] K |
| Other designations | |
| μ Sgr A: HD 166937, HIP 89341, HR 6812, PPM 268080, BD−21°4908, FK5 682, GC 24856 | |
| μ Sgr D: HD 314059, BD−21°4907 | |
| μ Sgr E: HD 314057, BD−21°4909, 2MASS J18134906-2103528 | |
| Database references | |
| SIMBAD | μ Sgr AB |
| μ Sgr D | |
| μ Sgr E | |
System
editThe 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
editμ 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).[14]
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".[15]
In 2016, the IAU organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[17] 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.[13]
In Chinese, 斗 (Dǒu), 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 斗宿三 (Dǒu Sù sān, English: the Third Star of Dipper.)[18]
Properties
editVariability
editMu 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).[10] In addition, it shows more irregular variations typical of an Alpha Cygni variable, irregularly pulsating hot supergiant stars.
Physical
editMu 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. Its mass is 23 times the solar mass while it has a surface temperature of 11,100 K. Mu Sagitarii 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,[19] 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.[20][21]
Component D has an early B spectral type, near B3.[22] 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.[23][8]
References
edit- ^ a b Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
- ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
- ^ Fraser, M.; Dufton, P. L.; Hunter, I.; Ryans, R. S. I. (2010). "Atmospheric parameters and rotational velocities for a sample of Galactic B-type supergiants". Monthly Notices of the Royal Astronomical Society. 404 (3): 1306. arXiv:1001.3337. Bibcode:2010MNRAS.404.1306F. doi:10.1111/j.1365-2966.2010.16392.x. S2CID 118674151.
- ^ a b Zasche, P.; Wolf, M.; Hartkopf, W. I.; Svoboda, P.; Uhlař, R.; Liakos, A.; Gazeas, K. (2009). "A Catalog of Visual Double and Multiple Stars with Eclipsing Components". The Astronomical Journal. 138 (2): 664. arXiv:0907.5172. Bibcode:2009AJ....138..664Z. doi:10.1088/0004-6256/138/2/664. S2CID 17089387.
- ^ a b c d e f g h i j k l Echevarria, J.; Roth, M.; Warman, J. (1979). "Photometric Study of Trapezium-Type Systems". Revista Mexicana de Astronomía y Astrofísica. 4: 287. Bibcode:1979RMxAA...4..287E.
- ^ a b Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
- ^ a b c d e f g h Abt, H. A.; Cardona, O. (1983). "Confirmation among visual multiples of an increase of AP stars with age". Astrophysical Journal. 272: 182. Bibcode:1983ApJ...272..182A. doi:10.1086/161276.
- ^ a b c d e f g Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c Lindroos, K. P. (1985). "A study of visual double stars with early type primaries. IV Astrophysical data". Astronomy and Astrophysics Supplement Series. 60: 183. Bibcode:1985A&AS...60..183L.
- ^ a b c d e f g h Polidan, R. S.; Plavec, M. J. (1984). "A hot companion to MU Sagittarii - an opportunity to sound the atmosphere of a B8 IA supergiant". Astronomical Journal. 89: 1721. Bibcode:1984AJ.....89.1721P. doi:10.1086/113678.
- ^ a b c Kaler, Jim. "Polis". stars.astro.illinois.edu. Retrieved 2024-08-13.
- ^ a b c d Lindroos, K. P. (1986). "A study of visual double stars with early-type primaries. V - Post-T Tauri secondaries". Astronomy and Astrophysics. 156: 223. Bibcode:1986A&A...156..223L.
- ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
- ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
- ^ 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.
- ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
- ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日 Archived 2011-05-22 at the Wayback Machine
- ^ Lindroos, K. P. (1983). "A study of visual double stars with early type primaries. II - Photometric results". Astronomy and Astrophysics Supplement Series. 51: 161. Bibcode:1983A&AS...51..161L.
- ^ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
- ^ Dommanget, J.; Nys, O. (1994). "Catalogue of the Components of Double and Multiple stars (CCDM). First edition". Obs. R. Belg. 115. Bibcode:1994CoORB.115.....D.
- ^ Nesterov, V. V.; Kuzmin, A. V.; Ashimbaeva, N. T.; Volchkov, A. A.; Röser, S.; Bastian, U. (1995). "The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars". Astronomy and Astrophysics. 110: 367. Bibcode:1995A&AS..110..367N.
- ^ Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.