Astronomy:W Sagittarii
  | |
| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 05m 01.22643s[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 | |
| Proper motion (μ) | RA: +4.372[1] mas/yr Dec.: −5.588[1] mas/yr |
| Parallax (π) | 2.365 ± 0.1765[1] mas |
| 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[6] R☉ |
| Luminosity | 2,690[5] L☉ |
| Surface gravity (log g) | 1.50 - 2.15[7] cgs |
| Temperature | 5,380 - 6,474[7] K |
| Metallicity [Fe/H] | +0.02[8] dex |
| Aa2 | |
| Mass | 1.4 - 2.0[4] M☉ |
| Ab | |
| Mass | 2.2[5] M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
W Sagittarii, also named Dhanusaragra,[9] 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 γ2 Sgr (Alnasl) which marks the nozzle or spout of the teapot asterism.
Nomenclature
W Sagittarii (abbreviated W Sgr) is this star's variable star designation; it also has the Bayer designation Gamma1 Sagittarii (γ1 Sagittarii, γ1 Sgr).
Dhanuśarāgra (धनुशराग्र), the Arrow, is an Indian star name used since the 14th century for the pair γ1 and γ2 Sgr, the latter having the Arabic name Alnasl.[10] The IAU Working Group on Star Names adopted the name Dhanusaragra for γ1 Sgr Aa1 on 13 August 2026.[9]
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.[11]
Component A, W Sgr, is itself a triple star system, with the components referred to as W Sgr Aa1, Aa2, and Ab.[12] These have also been referred to as components Aa, Ab, and B respectively.[11] 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☉.[11]
Variability
In early June of 1866, Johann Friedrich Julius Schmidt discovered that the star is a variable star.[14] The supergiant component W Sgr Aa1 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
- ↑ 1.0 1.1 1.2 1.3 1.4 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G. Gaia EDR3 record for this source at VizieR.
- ↑ 2.0 2.1 2.2 Samus, N. N. 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.
- ↑ 3.0 3.1 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.
- ↑ 4.0 4.1 4.2 Benedict, G. Fritz; McArthur, Barbara E.; Feast, Michael W.; Barnes, Thomas G.; Harrison, Thomas E.; Patterson, Richard J.; Menzies, John W.; Bean, Jacob L. et al. (2007). "Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic Cepheid Variable Stars: Period-Luminosity Relations". The Astronomical Journal 133 (4): 1810. doi:10.1086/511980. Bibcode: 2007AJ....133.1810B.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 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. doi:10.1088/0004-6256/146/4/93. Bibcode: 2013AJ....146...93E.
- ↑ 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. doi:10.1051/0004-6361:20078225. Bibcode: 2007A&A...474..975G.
- ↑ 7.0 7.1 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. doi:10.1086/420991. Bibcode: 2004AJ....128..343L.
- ↑ 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. doi:10.1134/S1063773713120050. Bibcode: 2013AstL...39..851M.
- ↑ 9.0 9.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/.
- ↑ "Dhanuśarāgra (धनुशराग्र)". IAU Working Group on Star Names. https://ase.exopla.net/index.php/Dhanusaragra.
- ↑ 11.0 11.1 11.2 Evans, Nancy Remage; Massa, Derck; Proffitt, Charles (2009). "Massive Star Multiplicity: The Cepheid W Sgr". The Astronomical Journal 137 (3): 3700. doi:10.1088/0004-6256/137/3/3700. Bibcode: 2009AJ....137.3700E.
- ↑ 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. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M.
- ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html.
- ↑ Schönfeld, E.. "Bemerkungen und Nachtrage zum Catalog von veranderlichen Sternen (in German)". Oberösterreichische Landesmuseen. https://www.zobodat.at/pdf/Jber-Mannheimer-Ver-Naturkunde_34_0080-0099.pdf.
 |  |
