Theta1 Sagittarii

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Theta1 Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg
Location of θ1 Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 19h 59m 44.17834s[1]
Declination −35° 16′ 34.7049″[1]
Apparent magnitude (V) 4.37[2]
Spectral type B3 IVp[3]
U−B color index −0.67[2]
B−V color index −0.15[2]
Proper motion (μ) RA: +5.60[1] mas/yr
Dec.: −25.81[1] mas/yr
Parallax (π)6.29 ± 0.21[1] mas
Distance520 ± 20 ly
(159 ± 5 pc)
Absolute magnitude (MV)−1.63[4]
Period (P)2.1051 d
Eccentricity (e)0.00
Periastron epoch (T)2411140.645 JD
Argument of periastron (ω)
Semi-amplitude (K1)
15.9 km/s
θ1 Sgr A
Mass6.6±0.1[6] M
Radius5.6[7] R
Luminosity (bolometric)2,271[8] L
Temperature17,900[8] K
Rotational velocity (v sin i)73[3] km/s
Age32.8±5.0[6] Myr
Other designations
θ1 Sgr, CD−35° 13831, HD 189103, HIP 98412, HR 7623, SAO 211716, WDS J19597-3517[9]
Database references

Theta1 Sagittarii (θ1 Sagittarii) is a close binary star[10] system in the zodiac constellation of Sagittarius. It is visible to the naked eye with an apparent visual magnitude of 4.37.[2] Based upon an annual parallax shift of 6.29 mas as seen from Earth,[1] this star is located around 520 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.24 due to interstellar dust.[11]

This is a single-lined spectroscopic binary with an orbital period of just 2.1 days in a circular orbit.[5] The visible member, component A, is a B-type subgiant star with a stellar classification of B3 IVp.[3] It is around 33[6] million years old and is spinning with a projected rotational velocity of 73 km/s.[3] The primary has 6.6[6] times the mass of the Sun and about 5.6[7] times the Sun's radius. It is radiating 2,271[8] times the solar luminosity from its photosphere at an effective temperature of 17,900 K.[8]


  1. ^ a b c d e f 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.
  2. ^ a b c d 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.
  3. ^ a b c d Levato, H. (1975), "Rotational velocities and spectral types for a sample of binary systems", Astronomy and Astrophysics, 19: 91, Bibcode:1975A&AS...19...91L
  4. ^ 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.
  5. ^ a b Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
  6. ^ a b c d Tetzlaff, N.; et al. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x.
  7. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (Third ed.), 367: 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  8. ^ a b c d Hohle, M. M.; et al. (2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355.
  9. ^ "tet01 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-07.
  10. ^ 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.
  11. ^ Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035.