Pi Sagittarii (π Sagittarii, abbreviated Pi Sgr, π Sgr) is a triple star system in the zodiac constellation of Sagittarius. It has an apparent visual magnitude of +2.89,[2] bright enough to be readily seen with the naked eye. Based upon parallax measurements, it is roughly 510 light-years (160 parsecs) from the Sun.[1]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 09m 45.83293s[1] |
| Declination | –21° 01′ 25.0103″[1] |
| Apparent magnitude (V) | +2.89[2] |
| Characteristics | |
| Spectral type | F2 II[2] |
| U−B color index | +0.22[3] |
| B−V color index | +0.35[3] |
| Astrometry | |
| Radial velocity (Rv) | –9.8[4] km/s |
| Proper motion (μ) | RA: –1.36[1] mas/yr Dec.: –36.45[1] mas/yr |
| Parallax (π) | 6.2410 ± 0.2868 mas[5] |
| Distance | 520 ± 20 ly (160 ± 7 pc) |
| Absolute magnitude (MV) | −3.08[6] |
| Details | |
| Mass | 5.9 ± 0.3[2] M☉ |
| Surface gravity (log g) | 2.21 ± 0.05[2] cgs |
| Temperature | 6,590 ± 50[2] K |
| Rotational velocity (v sin i) | 30[7] km/s |
| Age | 67[2] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The three components are designated Pi Sagittarii A (officially named Albaldah /ælˈbɔːldə/, from the traditional name of the entire system),[9] B and C.[8]
Nomenclature
editπ Sagittarii (Latinised to Pi Sagittarii) is the system's Bayer designation. The designations of the three constituents as Pi Sagittarii A, B and C, derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[10]
The system bore the traditional name Albaldah,[11] which comes from the Arabic بلدة bálda 'the town'.[12] In 2016, the IAU organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[14] It approved the name Albaldah for the component Pi Sagittarii A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[9]
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Nir al Beldat, which was translated into Latin as Lucida Oppidi, meaning 'the brightest of the town'.[15]
This system, together with Zeta Sagittarii and Sigma Sagittarii may have been the Akkadian Gu-shi-rab‑ba, 'the Yoke of the Sea'.[11]
In Chinese, 建 (Jiàn), meaning Establishment, refers to an asterism consisting of Pi Sagittarii, Xi² Sagittarii, Omicron Sagittarii, 43 Sagittarii, Ro¹ Sagittarii and Upsilon Sagittarii. Consequently, the Chinese name for Pi Sagittarii itself is 建三 (Jiàn sān, English: the Third Star of Establishment.)[16]
Properties
editThe spectrum of the system's primary, Pi Sagitarii A, matches a stellar classification of F2 II.[2] The 'II' luminosity class is for a bright giant star that has exhausted the hydrogen at its core and has followed an evolutionary track away from the main sequence of stars like the Sun. Because it has nearly six times the mass of the Sun,[2] it reached this stage in a mere 67 million years.[2] The outer envelope is radiating energy at an effective temperature of about 6,590 K,[2] giving it the yellow-white hue of an F-type star.[17]
Pi Sagittarii A has two nearby companions. The first is separated by 0.1 arcseconds, or at least 13 AUs. The second is 0.4 arcseconds away, which is 40 AU or more. Nothing is known about the orbits of these stars.[12]
Being 1.43 degrees north of the ecliptic, Pi Sagittarii can be occulted by the Moon, and, very rarely, by planets. The next occultation by a planet will be by Venus on February 17, 2035.[18]
References
edit- ^ a b c d e van Leeuwen, F. (November 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
- ^ a b c d e f g h i j k Lyubimkov, Leonid S.; et al. (February 2010), "Accurate fundamental parameters for A-, F- and G-type Supergiants in the solar neighbourhood", Monthly Notices of the Royal Astronomical Society, 402 (2): 1369–1379, arXiv:0911.1335, Bibcode:2010MNRAS.402.1369L, doi:10.1111/j.1365-2966.2009.15979.x, S2CID 119096173
- ^ a b Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N
- ^ Wilson, R. E. (1953), "General Catalogue of Stellar Radial Velocities", Carnegie Institute Washington D.C. Publication, Carnegie Institute of Washington, D.C., Bibcode:1953GCRV..C......0W
- ^ Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
- ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
- ^ Bernacca, P. L.; Perinotto, M. (1970), "A Catalogue of Stellar Rotational Velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1): 1, Bibcode:1970CoAsi.239....1B
- ^ a b "CCDM J19098-2101AB -- Double or multiple star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-01-15
- ^ 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].
- ^ a b Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 355. ISBN 0-486-21079-0. Retrieved 2012-09-04.
- ^ a b Kaler, James B., "ALBALDAH (Pi Sagitarii)", Stars, University of Illinois, retrieved 2012-01-21
- ^ "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.
- ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55 (8): 429–438. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
- ^ (in Chinese) 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
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on November 8, 2004, retrieved 2012-01-16
- ^ Grego, Peter (2008), "7. Observing Venus", Venus and Mercury, and How to Observe Them, Astronomers' Observing Guides, New York, NY: Springer, pp. 229–247, doi:10.1007/978-0-387-74286-1_7, ISBN 978-0-387-74285-4