Theta Sagittae

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Theta Sagittae
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg
Location of θ Sagittae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagitta
Right ascension 20h 09m 56.6468s[1]
Declination +20° 54′ 54.098″[1]
Apparent magnitude (V) +6.48[2]
Spectral type F5 IV[3]
U−B color index −0.04[1]
B−V color index +0.38[1]
Radial velocity (Rv)−43.0[4] km/s
Proper motion (μ) RA: +59.68[5] mas/yr
Dec.: +98.43[5] mas/yr
Parallax (π)22.15 ± 0.43[5] mas
Distance147 ± 3 ly
(45.1 ± 0.9 pc)
Absolute magnitude (MV)+3.24[6]
Mass1.52[7] M
Luminosity4.25[6] L
Surface gravity (log g)4.32[7] cgs
Temperature6,750±229[7] K
Metallicity [Fe/H]−0.17[4] dex
Rotational velocity (v sin i)33.6[8] km/s
Age2.089[7] Gyr
Other designations
θ Sge, 17 Sge, BD+20° 4453, HD 191570, HIP 99352, HR 7705, SAO 88276, WDS J20099+2055A[9]
Database references

Theta Sagittae (θ Sagittae) is a double star[10] in the northern constellation of Sagitta. With an apparent visual magnitude of +6.48,[2] it is near the limit of stars that can be seen with the naked eye. According to the Bortle scale the star is visible in dark suburban/rural skies. Based upon an annual parallax shift of 22.15 mas as seen from Earth,[5] it is located roughly 147 light years from the Sun.

The primary, component A,[11] is an F-type subgiant star with a stellar classification of F5 IV.[3] This star is about two[7] billion years old with 52%[7] more mass than the Sun. It forms a double star with a magnitude 8.85[11] companion, which is located at an angular separation of 11.58 arc seconds along a position angle of 331.1°, as of 2011.[10]


  1. ^ a b c d Gaia Collaboration; et al. (November 2016), "Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties", Astronomy & Astrophysics, 595: 23, arXiv:1609.04172, Bibcode:2016A&A...595A...2G, doi:10.1051/0004-6361/201629512, A2.
  2. ^ a b 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 Harlan, E. A. (September 1969), "MK classifications for F- and G-type stars. I", Astronomical Journal, 74: 916–919, Bibcode:1969AJ.....74..916H, doi:10.1086/110881.
  4. ^ a b Casagrande, L.; et al. (2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy & Astrophysics, 530 (A138): 21, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276.
  5. ^ a b c d 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.
  6. ^ a b 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.
  7. ^ a b c d e f David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  8. ^ do Nascimento, J. D., Jr.; et al. (July 2003), "On the link between rotation, chromospheric activity and Li abundance in subgiant stars", Astronomy and Astrophysics, 405: 723–731, arXiv:astro-ph/0307196, Bibcode:2003A&A...405..723D, doi:10.1051/0004-6361:20030633.
  9. ^ "tet Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-10.
  10. ^ a b Mason, Brian D.; et al. (May 2012), "Speckle Interferometry at the U.S. Naval Observatory. XVIII", The Astronomical Journal, 143 (5): 6, Bibcode:2012AJ....143..124M, doi:10.1088/0004-6256/143/5/124, 124.
  11. ^ a b Mason, B. D.; et al. (2014), The Washington Visual Double Star Catalog, Bibcode:2001AJ....122.3466M, doi:10.1086/323920