Psi Sagittarii

Psi Sagittarii, which is Latinized from ψ Sagittarii, is a triple star[8] system in the zodiac constellation of Sagittarius. The star system is located at a distance of 298 light years from the Earth based on parallax, but is drifting closer with a heliocentric radial velocity of −12 km/s.[4] The system is faintly visible to the naked eye has a combined apparent visual magnitude of +4.86.[2]

Psi Sagittarii
Location of ψ Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 19h 15m 32.42658s[1]
Declination −25° 15′ 24.0569″[1]
Apparent magnitude (V) +4.86[2]
Characteristics
Spectral type K2 III + A9 III + A3 V[3]
B−V color index 0.569±0.006[2]
Astrometry
Radial velocity (Rv)−11.43±1.47[4] km/s
Proper motion (μ) RA: +45.50[1] mas/yr
Dec.: −31.08[1] mas/yr
Parallax (π)10.93 ± 0.31[1] mas
Distance298 ± 8 ly
(91 ± 3 pc)
Absolute magnitude (MV)0.06[2]
Orbit[5]
Period (P)7,319 d
Eccentricity (e)0.51
Periastron epoch (T)2442418.795 JD
Argument of periastron (ω)
(secondary)		2.6°
Semi-amplitude (K1)
(primary)		10.0 km/s
Semi-amplitude (K2)
(secondary)		13.8 km/s
Details
A
Mass2.10[6] M☉
Luminosity84[2] L☉
Ba/Bb
Mass1.70/2.70 M☉
Other designations
ψ Sgr, 42 Sgr, CPD−27° 6737, HD 179950, HIP 94643, HR 7292, SAO 187882, WDS J19155-2515[7]
Database references
SIMBADdata

The inner pair of this triple star system, components Ba and Bb, have an orbital period of 10.78 days and an eccentricity of 0.47.[8] The pair consist of an A-type giant and a less evolved A-type main-sequence star with stellar classifications of A9 III + A3 V,[3] respectively. These in turn share an orbit with the primary, component A, having a period of 20 years and an eccentricity of 0.51.[5] The last is an orange-hued K-type giant with a class of K2 III.[3]

Name and etymology

According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, this star was titled as Al Kiladah.[9] This star, together with τ Sgr, ν Sgr, ω Sgr, 60 Sgr and ζ Sgr were Al Udḥiyy, the Ostrich's Nest.[10]

References
  1. 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.
  2. 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.
  3. Docobo, José A.; Andrade, Manuel (November 2006), "A Methodology for the Description of Multiple Stellar Systems with Spectroscopic Subcomponents", The Astrophysical Journal, 652 (1): 681–695, Bibcode:2006ApJ...652..681D, doi:10.1086/508053.
  4. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy & Astrophysics, 424 (2): 727–732, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213, S2CID 119387088.
  6. Tokovinin, A. (September 2008), "Comparative statistics and origin of triple and quadruple stars", Monthly Notices of the Royal Astronomical Society, 389 (2): 925–938, arXiv:0806.3263, Bibcode:2008MNRAS.389..925T, doi:10.1111/j.1365-2966.2008.13613.x, S2CID 16452670.
  7. "psi Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-02.
  8. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  9. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), California Institute of Technology: Jet Propulsion Laboratory, retrieved 2017-07-02.
  10. 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.
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