HD 219617
Binary star system in the constellation Aquarius
From Wikipedia, the free encyclopedia
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.[5] Another theory suggests that the binary star is composed of subgiant stars.[10] 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.[9] The stellar chemical composition is peculiar, being relatively oxygen-enriched[11] and extremely depleted in neutron capture elements.[7] The helium fraction of the binary star at present cannot be reliably determined, and appears to be near the primordial helium abundance.[12]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius[1] |
| Right ascension | 23h 17m 05.0438s[2] |
| Declination | −13° 51′ 03.597″[2] |
| Apparent magnitude (V) | 8.14[2] |
| Characteristics | |
| HD 219617A | |
| Spectral type | sdF5[3] |
| HD 219617B | |
| Spectral type | sdF6[3] |
| Astrometry | |
| Radial velocity (Rv) | 13.28±0.35[4] km/s |
| Parallax (π) | 15.08±1.8 mas[5] |
| Distance | approx. 220 ly (approx. 66 pc) |
| Absolute magnitude (MV) | +4.89[1] |
| Orbit[5] | |
| Primary | HD 219617A |
| Name | HD 219617B |
| Period (P) | 388+34 −24 y |
| Semi-major axis (a) | 0.957+0.053 −0.041″ |
| Eccentricity (e) | 0.464+0.040 −0.041 |
| Inclination (i) | 86.93+0.07 −0.06° |
| Details | |
| HD 219617A | |
| Mass | 1.126+0.004 −0.005[5] M☉ |
| Surface gravity (log g) | 4.30[6] cgs |
| Temperature | 5825[6] K |
| Metallicity [Fe/H] | −1.45[7] dex |
| Rotational velocity (v sin i) | 6.2[8] km/s |
| Age | 16.14+0.81 −0.78[9] Gyr |
| HD 219617B | |
| Mass | 1.068±0.004[5] M☉ |
| Surface gravity (log g) | 4.30[6] cgs |
| Other designations | |
| BD−14 6437, HIP 114962, ADS 16644, 2MASS J23170501-1351046, Gaia EDR3 2411728178376670976[2] | |
| HD 219617A: TYC 5827-1181-2 | |
| HD 219617B: TYC 5827-1181-1 | |
| Database references | |
| SIMBAD | data |
| A | |
| B | |
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[13] at a projected separation of 19″ (1,200 AU).[10] VB 12 also has several peculiarities.[10] The star system belongs kinematically to the halo stars. Additional stellar components of the star system are suspected.[5]
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.[14][12] Then in 2017, the orbit was measured accurately, as separation between the stars increased.[5]