W Sagittarii

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This article is about γ1 Sagittarii. For other stars with this Bayer designation, see γ Sagittarii.
W Sagittarii
Sagittarius constellation map.svg
Red circle.svg

Location of W Sgr (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Sagittarius
Right ascension 18h 05m 01.22409s[1]
Declination −29° 34′ 48.3199″[1]
Apparent magnitude (V) 4.29 - 5.14[2]
Spectral type F4 - G2Ib[2] + ~F5V[3]
U−B color index +0.52[4]
B−V color index +0.78[4]
Variable type δ Cep[2]
Spectral type A0 V[3]
Radial velocity (Rv) –28.04[5] km/s
Proper motion (μ) RA: +2.62[1] mas/yr
Dec.: –5.28[1] mas/yr
Parallax (π) 2.28 ± 0.20[6] mas
Distance 409[3] pc
Absolute magnitude (MV) −3.76[3]
Primary Aa
Companion Ab
Period (P) 1,582 ± 3 days
Semi-major axis (a) 12.9 ± 0.3"
(5.67 ± 0.13 AU)
Eccentricity (e) 0.41 ± 0.02
Inclination (i) 7.0 ± 0.8°
Longitude of the node (Ω) 68.4 ± 4.0°
Periastron epoch (T) 2004.16 ± 0.01
Argument of periastron (ω)
328.0 ± 1.3°
Primary A
Companion B
Period (P) 172.9 yr
Semi-major axis (a) 63 AU
Mass 5.8[3] M
Radius 61.0[7] R
Luminosity 2,690[3] L
Surface gravity (log g) 1.50 - 2.15[8] cgs
Temperature 5,380 - 6,474[8] K
Metallicity [Fe/H] +0.02[9] dex
Mass 2.2[3] M
Other designations
γ1 Sgr, W Sagittarii, HR 6742, HD 164975, SAO 186237, HIP 88567, ADS 11029, CCDM 18050-2935
Database references

W Sagittarii (W Sgr, Gamma-1 Sagittarii (γ¹ Sgr)) is a multiple star system star in the constellation Sagittarius. It is an optical line-of-sight companion to the much brighter Al Nasl2 Sgr) which marks the "nozzle" ("spout") of the "teapot" asterism forming a large part of Sagittarius. The primary star is a supergiant Classical Cepheid variable.


W Sgr is listed as component A of a multiple star system catalogued as ADS 11029 and WDS J18050-2935. Components B and C are at 33" and 46" respectively and both are 13th magnitude. They are purely optical companions, not physically associated with W Sgr.[10]

Component A, W Sgr, is itself a triple star system, with the components referred to as W Sgr Aa, Ab, and B. The outer companion B has been resolved at a separation of 0.14" and is over 5 magnitudes fainter than the primary supergiant. The inner components can only be identified spectroscopically by their radial velocity variations. The primary is a 6 M yellow supergiant, while the secondary is an early F main sequence star with a mass less than 1.4 M.[10]


The supergiant component W Sgr Aa is a variable star which pulsates regularly between magnitudes 4.3 and 5.1 every 7.59 days. During the pulsations, that temperature and spectral type also vary. It is classified as a Classical Cepheid (δ Cephei) variable.[3]


  1. ^ a b c d Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c 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. 
  3. ^ a b c d e f g h i Remage Evans, Nancy; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Karovska, Margarita; Tingle, Evan (2013). "Binary Cepheids: Separations and Mass Ratios in 5 M ⊙ Binaries". The Astronomical Journal. 146 (4): 93. arXiv:1307.7123Freely accessible. Bibcode:2013AJ....146...93R. doi:10.1088/0004-6256/146/4/93. 
  4. ^ a b 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. 
  5. ^ Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727. arXiv:astro-ph/0406573Freely accessible. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. 
  6. ^ a b Benedict, G. Fritz; McArthur, Barbara E.; Feast, Michael W.; Barnes, Thomas G.; Harrison, Thomas E.; Patterson, Richard J.; Menzies, John W.; Bean, Jacob L.; Freedman, Wendy L. (2007). "Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations". The Astronomical Journal. 133 (4): 1810. arXiv:astro-ph/0612465Freely accessible. Bibcode:2007AJ....133.1810B. doi:10.1086/511980. 
  7. ^ Groenewegen, M. A. T. (2007). "The projection factor, period-radius relation, and surface-brightness colour relation in classical cepheids". Astronomy and Astrophysics. 474 (3): 975. Bibcode:2007A&A...474..975G. doi:10.1051/0004-6361:20078225. 
  8. ^ a b Luck, R. E.; Andrievsky, S. M. (2004). "Phase-dependent Variation of the Fundamental Parameters of Cepheids. I. Periods from 6 to 10 Days". The Astronomical Journal. 128: 343. Bibcode:2004AJ....128..343L. doi:10.1086/420991. 
  9. ^ Marsakov, V. A.; Koval', V. V.; Kovtyukh, V. V.; Mishenina, T. V. (2013). "Properties of the population of classical Cepheids in the Galaxy". Astronomy Letters. 39 (12): 851. Bibcode:2013AstL...39..851M. doi:10.1134/S1063773713120050. 
  10. ^ a b Evans, Nancy Remage; Massa, Derck; Proffitt, Charles (2009). "Massive Star Multiplicity: The Cepheid W Sgr". The Astronomical Journal. 137 (3): 3700. arXiv:0902.3281Freely accessible. Bibcode:2009AJ....137.3700E. doi:10.1088/0004-6256/137/3/3700.