Eta Sagittae

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η Sagittae
Sagitta constellation map.svg
Red circle.svg
Location of η Sagittae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagitta
Right ascension 20h 05m 09.49303s[1]
Declination +19° 59′ 27.8575″[1]
Apparent magnitude (V) +5.09[2]
Spectral type K2 III[3]
U−B color index +0.98[2]
B−V color index +1.06[2]
Radial velocity (Rv)−40.53[4] km/s
Proper motion (μ) RA: +29.962±0.173[4] mas/yr
Dec.: +80.440±0.173[4] mas/yr
Parallax (π)20.9262 ± 0.1208[4] mas
Distance155.9 ± 0.9 ly
(47.8 ± 0.3 pc)
Absolute magnitude (MV)1.61[5]
Mass1.73±0.09 M
Radius7.08±0.21 R
Luminosity26 L
Surface gravity (log g)3.03±0.10 cgs
Temperature4,784±3.03 K
Metallicity [Fe/H]+0.10 dex
Rotational velocity (v sin i)1.3[5] km/s
Age1.69±0.25 Gyr
Other designations
η Sge, 16 Sge, BD+19°4277, FK5 3609, GC 27868, HD 190608, HIP 98920, HR 7679, SAO 105659, PPM 137588[7]
Database references

Eta Sagittae (η Sagittae) is solitary[8] star in the northern constellation of Sagitta. It is faintly visible to the naked eye, having an apparent visual magnitude of +5.09.[2] Based upon an annual parallax shift of 20.34 mas,[1] it is approximately 160 light years distant from the Sun. There is a 61.1% chance that it is a member of the Hyades-Pleiades stream of stars that share a common motion through space.[9]

This is an evolved K-type giant star with a stellar classification of K2 III.[3] At the age of about 1.7 billion years,[6] it is now a red clump star that is generating energy through the fusion of helium at its core.[10] Eta Sagittae has 1.7 times the mass of the Sun and has expanded to seven times the Sun's radius. It is radiating 25.7 times the Sun's luminosity from its photosphere at an effective temperature of 4,784 K.[6]


  1. ^ a b c 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, S2CID 18759600.
  2. ^ a b c d Argue, A. N. (1966), "UBV photometry of 550 F, G and K type stars", Monthly Notices of the Royal Astronomical Society, 133 (4): 475–493, Bibcode:1966MNRAS.133..475A, doi:10.1093/mnras/133.4.475.
  3. ^ a b Roman, Nancy G. (July 1952), "The Spectra of the Bright Stars of Types F5-K5", Astrophysical Journal, 116: 122, Bibcode:1952ApJ...116..122R, doi:10.1086/145598.
  4. ^ a b c d Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. ^ a b Setiawan, J.; et al. (July 2004), "Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch", Astronomy and Astrophysics, 421: 241–254, Bibcode:2004A&A...421..241S, doi:10.1051/0004-6361:20041042-1.
  6. ^ a b c Maldonado, J.; et al. (June 2013), "The metallicity signature of evolved stars with planets", Astronomy & Astrophysics, 554: 18, arXiv:1303.3418, Bibcode:2013A&A...554A..84M, doi:10.1051/0004-6361/201321082, S2CID 119289111, A84.
  7. ^ "eta Sge". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-11.
  8. ^ 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, S2CID 14878976.
  9. ^ Famaey, B.; et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430: 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272, S2CID 17804304.
  10. ^ Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.