Delta Horologii
Binary star system in the constellation Horologium
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Delta Horologii (δ Horologii) is a binary star[3] system in the constellation Horologium. It is visible to the naked eye with a combined apparent visual magnitude of 4.93.[2] Based upon an annual parallax shift of 18.24 mas as seen from Earth,[1] it is located 179 ± 4 light years from the Sun.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Horologium |
| Right ascension | 04h 10m 50.58927s[1] |
| Declination | −41° 59′ 36.8537″[1] |
| Apparent magnitude (V) | 4.93[2] (5.15 + 7.29)[3] |
| Characteristics | |
| Spectral type | A9 V[3] |
| U−B color index | +0.084[2] |
| B−V color index | +0.338[2] |
| Astrometry | |
| Radial velocity (Rv) | +38.3±2.6[4] km/s |
| Proper motion (μ) | RA: +199.08[1] mas/yr Dec.: +70.18[1] mas/yr |
| Parallax (π) | 18.24±0.41 mas[1] |
| Distance | 179 ± 4 ly (55 ± 1 pc) |
| Absolute magnitude (MV) | 1.50[5] |
| Orbit[6] | |
| Period (P) | 23.80±0.74 yr |
| Semi-major axis (a) | 0.224±0.013″ |
| Eccentricity (e) | 0.582±0.014 |
| Inclination (i) | 110.6±2.5° |
| Longitude of the node (Ω) | 193.0±1.6° |
| Periastron epoch (T) | 2018.95±0.18 |
| Argument of periastron (ω) (secondary) | 284.3±3.5° |
| Details | |
| δ Hor A | |
| Mass | 1.41[7] M☉ |
| Surface gravity (log g) | 3.71±0.14[7] cgs |
| Temperature | 7,033±239[7] K |
| Metallicity [Fe/H] | −0.32[8] dex |
| Rotational velocity (v sin i) | 220.1±11.0[5] km/s |
| Age | 768[7] Myr |
| δ Hor B | |
| Rotational velocity (v sin i) | 51.7±2.6[5] km/s |
| Other designations | |
| δ Hor, CD−42°1400, HD 26612, HIP 19515, HR 1302, SAO 216682, WDS J04108-4200AB[9] | |
| Database references | |
| SIMBAD | data |
The two components orbit around each other with a period of 23.8 years and a somewhat high eccentricity of 0.58.[6] The primary, component A, is a magnitude 5.15 A-type main sequence star with a stellar classification of A9 V.[3] At the estimated age of 768 million years,[7] it is spinning rapidly with a projected rotational velocity of 220 km/s,[5] giving the star an oblate shape with an equatorial bulge that is 15% larger than the polar radius.[10] The star has 1.4[7] times the mass of the Sun.
The secondary has an apparent magnitude of 7.29.[3]