Short description: Binary star system in the constellation Aquarius
Coordinates: 
23h 17m 05.0438s, −13° 51′ 03.5971″
HD 219617 is a binary star system some 220 light-years away from the Solar System in the constellation Aquarius. It is composed of two metal-poor F-type subdwarf stars orbiting each other in a 388-year orbit.[3] Another theory suggests that the binary star is composed of subgiant stars.[4] Unlike many halo stars, which exhibit an excess of alpha elements relative to iron, HD 219617 is depleted in iron peak and alpha elements, although alpha elements concentrations are poorly constrained.[8] The stellar chemical composition is peculiar, being relatively oxygen-enriched[9] and extremely depleted in neutron capture elements.[6] The helium fraction of the binary star at present cannot be reliably determined, and appears to be near the primordial helium abundance.[10]
The binary star HD 219617 is part of the hierarchical triple system LDS 6393, together with the red subdwarf VB 12 (LHS 541) of spectral class sdM3[11] at a projected separation of 19″ (1,200 AU).[4] VB 12 also has several peculiarities.[4] The star system belongs kinematically to the halo stars. Additional stellar components of the star system are suspected.[3]
The binary nature of HD 219617 has been known since the 19th century, but uncertainties in measurement and a stellar conjunction in 1920 precluded determining even an approximate orbit until 1991.[12][10] Then in 2017, the orbit was measured accurately, as separation between the stars increased.[3]
References
- ↑ 1.0 1.1 1.2 1.3 "HD 219617". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HD+219617.
- ↑ Navarrete, Camila; Chanamé, Julio; Ramírez, Iván; Meza, Andrés; Anglada-Escudé, Guillem; Shkolnik, Evgenya (2015), "The Kapteyn Moving Group is Not Tidal Debris from ω Centauri", The Astrophysical Journal 808 (1): 103–126, doi:10.1088/0004-637X/808/1/103, Bibcode: 2015ApJ...808..103N
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Mendez, Rene A.; Claveria, Ruben M.; Orchard, Marcos E.; Silva, Jorge F. (2017), "Orbits for 18 Visual Binaries and Two Double-line Spectroscopic Binaries Observed with HRCAM on the CTIO SOAR 4 m Telescope, Using a New Bayesian Orbit Code Based on Markov Chain Monte Carlo", The Astronomical Journal 154 (5): 187, doi:10.3847/1538-3881/aa8d6f, Bibcode: 2017AJ....154..187M
- ↑ 4.0 4.1 4.2 4.3 Krawchuk, C. A. P.; Dawson, P. C.; De Robertis, M. M. (2000), "Fundamental Parameters of Low-Mass Stars from Broadband Photometry. I. Method and First Results", The Astronomical Journal 119 (4): 1956–1967, doi:10.1086/301292, Bibcode: 2000AJ....119.1956K
- ↑ 5.0 5.1 5.2 5.3 Takeda, Yoichi; Takada-Hidai, Masahide (2011), "Chromospheres in Metal-Poor Stars Evidenced from the He I 10830Å Line", Publications of the Astronomical Society of Japan 63: 547, doi:10.1093/pasj/63.sp2.S547, Bibcode: 2011PASJ...63S.547T
- ↑ 6.0 6.1 Fishlock, C. K.; Yong, D.; Karakas, A. I.; Alves-Brito, A.; Meléndez, J.; Nissen, P. E.; Kobayashi, C.; Casey, A. R. (2017), "Sc and neutron-capture abundances in Galactic low- and high-α field halo stars", Monthly Notices of the Royal Astronomical Society 466 (4): 4672, doi:10.1093/mnras/stx047, Bibcode: 2017MNRAS.466.4672F
- ↑ De Medeiros, J. R.; Silva, J. R. P.; Do Nascimento Jr, J. D.; Canto Martins, B. L.; Da Silva, L.; Melo, C.; Burnet, M. (2006), "A catalog of rotational and radial velocities for evolved stars", Astronomy & Astrophysics 458 (3): 895–898, doi:10.1051/0004-6361:20065642
- ↑ 8.0 8.1 Ge, Z. S.; Bi, S. L.; Chen, Y. Q.; Li, T. D.; Zhao, J. K.; Liu, K.; Ferguson, J. W.; Wu, Y. Q. (2016), "Ages of 70 Dwarfs of Three Populations in the Solar Neighborhood: Considering O and C Abundances in Stellar Models", The Astrophysical Journal 833 (2): 161, doi:10.3847/1538-4357/833/2/161, Bibcode: 2016ApJ...833..161G
- ↑ Ramírez, I.; Meléndez, J.; Chanamé, J. (2012), "Oxygen Abundances in Low- and High-α Field Halo Stars and the Discovery of Two Field Stars Born in Globular Clusters", The Astrophysical Journal 757 (2): 164, doi:10.1088/0004-637X/757/2/164, Bibcode: 2012ApJ...757..164R
- ↑ 10.0 10.1 Smak, J. (1987), "On the helium content of the subdwarf binary ADS 16644", Acta Astronomica 37: 357, Bibcode: 1987AcA....37..357S
- ↑ Rajpurohit, A. S.; Reylé, C.; Allard, F.; Homeier, D.; Bayo, A.; Mousis, O.; Rajpurohit, S.; Fernández-Trincado, J. G. (2016), "Spectral energy distribution of M-subdwarfs: A study of their atmospheric properties", Astronomy and Astrophysics 596: A33, doi:10.1051/0004-6361/201526776, Bibcode: 2016A&A...596A..33R
- ↑ Heintz, W. D. (1991), "Orbits of visual binaries", Astronomy and Astrophysics Supplement Series 90: 311, Bibcode: 1991A&AS...90..311H
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