W Sagittarii

This article is about γ^1 Sagittarii. For other stars with this Bayer designation, see γ Sagittarii.

W Sagittarii

Location of W Sgr (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Sagittarius
Right ascension	18^h 05^m 01.22643^s[1]
Declination	−29° 34′ 48.3222″[1]
Apparent magnitude (V)	4.29 - 5.14[2]
Characteristics
Aa1
Spectral type	F4 - G2Ib[2]
U−B color index	+0.52[3]
B−V color index	+0.78[3]
Variable type	δ Cep[2]
Aa2
Spectral type	A5V - F5V[4]
Ab
Spectral type	A0 V[5]
Astrometry
Radial velocity (Rv)	−28.04[6] km/s
Proper motion (μ)	RA: +4.372[1] mas/yr Dec.: −5.588[1] mas/yr
Parallax (π)	2.365 ± 0.1765 mas[1]
Distance	1,400 ± 100 ly (420 ± 30 pc)
Absolute magnitude (MV)	−3.76[5]
Orbit[4]
Primary	Aa1
Companion	Aa2
Period (P)	4.33±0.01 yr
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) (secondary)	328.0 ± 1.3°
Orbit[5]
Primary	Aa
Companion	Ab
Period (P)	172.9 yr
Semi-major axis (a)	63 AU
Details
Aa
Mass	5.8[5] M☉
Radius	61.0[7] R☉
Luminosity	2,690[5] 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
Aa2
Mass	1.4 - 2.0[4] M☉
Ab
Mass	2.2[5] M☉
Other designations
γ^1 Sgr, W Sagittarii, HR 6742, HD 164975, SAO 186237, HIP 88567, ADS 11029, CCDM 18050-2935
Database references
SIMBAD	data

W Sagittarii (W Sgr, Gamma^1 Sagittarii (γ^1 Sgr)) is a multiple star system star in the constellation Sagittarius, and a Cepheid variable star.

W Sagittarii is an optical line-of-sight companion nearly a degree from the much brighter γ^2 Sgr (Al Nasl) which marks the nozzle or spout of the teapot asterism.

System

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 Aa1, Aa2, and Ab.[11] These have also been referred to as components Aa, Ab, and B respectively.[10] The outer companion Ab 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]

Variability

A light curve for W Sagittarii, plotted from TESS data[12]

The supergiant component W Sgr Aa1 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.[5]

References

1. 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.
2. 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. 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.
4. 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/0612465. Bibcode:2007AJ....133.1810B. doi:10.1086/511980. S2CID 16384267.
5. Evans, Nancy Remage; 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:1307.7123. Bibcode:2013AJ....146...93E. doi:10.1088/0004-6256/146/4/93. S2CID 34133110.
6. 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): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
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): 975–981. Bibcode:2007A&A...474..975G. doi:10.1051/0004-6361:20078225.
8. 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 (1): 343–356. 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. S2CID 119788977.
10. Evans, Nancy Remage; Massa, Derck; Proffitt, Charles (2009). "Massive Star Multiplicity: The Cepheid W Sgr". The Astronomical Journal. 137 (3): 3700. arXiv:0902.3281. Bibcode:2009AJ....137.3700E. doi:10.1088/0004-6256/137/3/3700. S2CID 3112765.
11. 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): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
12. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.