17 Sagittarii

17 Sagittarii is a binary star system in the zodiac constellation of Sagittarius, located 675 light years from the Sun. With a combined apparent visual magnitude of 6.89^[2] it is below the normal limit of visibility to the naked eye. The system is moving closer to the Earth with a heliocentric radial velocity of −14 km/s.^[1] J. Allen Hynek (1938) found an initial spectral type of G5 + A5 for the pair. It was first resolved by Harold A. McAlister (1978), who found an angular separation of 0.260″±0.002″ along a position angle of 133.0°±1.2°^[8]

17 Sagittarii

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Sagittarius
Right ascension	18h 16m 35.36860s[1]
Declination	−20° 32′ 40.1303″[1]
Apparent magnitude (V)	6.89[2] (7.24 + 8.89[3])
Characteristics
Spectral type	G8/K0 III[4] + A4::[5]
B−V color index	1.027±0.015[2]
Astrometry
Radial velocity (Rv)	−13.88±0.51[1] km/s
Proper motion (μ)	RA: 10.978[1] mas/yr Dec.: −14.342[1] mas/yr
Parallax (π)	4.8289 ± 0.0505 mas[1]
Distance	675 ± 7 ly (207 ± 2 pc)
Absolute magnitude (MV)	0.68[2]
Details
Luminosity	73.21[6] L☉
Temperature	4700[6] K
Other designations
17 Sgr, BD−20°5068, HD 167570, HIP 89567, SAO 186575, WDS 18166-2033[7]
Database references
SIMBAD	data

The magnitude 7.24^[3] primary component is an evolved giant star with a stellar classification of G8/K0 III,^[4] indicating it has exhausted the hydrogen at its core and expanded off the main sequence. It is radiating 73 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,700 K.^[6] The companion is a hot A-type star of uncertain luminosity class,^[5] with a visual magnitude of 8.89.^[3]

References

1. 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.
2. 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, S2CID 119257644.
3. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
4. Houk, Nancy; Smith-Moore, M. (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
5. Ginestet, N.; Carquillat, J. M. (2002), "Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components", The Astrophysical Journal Supplement Series, 143 (2): 513, Bibcode:2002ApJS..143..513G, doi:10.1086/342942.
6. McDonald, I.; et al. (2012), "Fundamental parameters and infrared excesses of Hipparcos stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–357, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
7. "17 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-22.
8. McAlister, H. A. (November 1, 1978), "Speckle interferometric measurements of binary stars. II", Astrophysical Journal, Part 1, 225: 932–938, Bibcode:1978ApJ...225..932M, doi:10.1086/156559. See note #25.